Thomas P. Andriacchi

All Publications

• Cartilage Oligomeric Matrix Protein Responses to a Mechanical Stimulus Associate with Ambulatory Loading in Individuals with Anterior Cruciate Ligament Reconstruction. Journal of orthopaedic research : official publication of the Orthopaedic Research Society Erhart-Hledik, J. C., Titchenal, M. R., Migliore, E., Asay, J. L., Andriacchi, T. P., Chu, C. R. 2021

  Abstract

  Mechanical factors have been implicated in the development of osteoarthritis after anterior cruciate ligament (ACL) reconstruction. This study tested for associations between ambulatory joint loading (total joint moment, TJM, and vertical ground reaction force, vGRF) and changes in serum levels of cartilage oligomeric matrix protein (COMP) in response to a mechanical stimulus (30-minute walk) in individuals with ACL reconstruction. Twenty-five subjects (mean age: 34.5±9.8 years; 2.2±0.2 years post-surgery) with primary unilateral ACL reconstruction underwent gait analysis for assessment of peak vGRF and TJM first (TJM1) and second (TJM2) peaks. Serum COMP concentrations were measured by enzyme-linked immunosorbent assay immediately before, 3.5-hours, and 5.5-hours after a 30-minute walk. Pearson correlation coefficients and backwards stepwise multiple linear regression analysis, with adjustments for age, sex, BMI and between-limb speed difference, assessed associations between changes in COMP and between limb-differences in joint loading parameters. Greater TJM1 (R=0.542, p=0.005), TJM2 (R=0.460, p=0.021), and vGRF (R=0.577,p=0.003) in the ACL-reconstructed limb as compared to the contralateral limb were associated with higher COMP values 3.5-hours following the 30-minute walk. Change in COMP at 5.5-hours became a significant predictor of the between-limb difference in TJM1 and vGRF in multivariate analyses after accounting for between-limb speed difference. These results demonstrate that higher TJM and vGRF in the ACLR limb as compared to the contralateral limb are associated with higher relative COMP levels 3.5-hours and 5.5-hours after a 30-minute walk. Future work should investigate the effect of therapies to alter joint loading on the biological response in individuals after ACL reconstruction. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/jor.25121

  View details for PubMedID 34185322

• Bridging Disciplines as a pathway to Finding New Solutions for Osteoarthritis a collaborative program presented at the 2019 Orthopaedic Research Society and the Osteoarthritis Research Society International. Osteoarthritis and cartilage open Andriacchi, T. P., Griffin, T. M., Loeser, R. F., Chu, C. R., Roos, E. M., Hawker, G. A., Erhart-Hledik, J. C., Fischer, A. G. 2020; 2 (1): 100026

  Abstract

  To stimulate future research directions that seek solutions for osteoarthritis (OA) at the interface between diverse disciplines and address osteoarthritis (OA) as a serious disease with a complexity that has presented a barrier to finding safe effective solutions.Sessions were conducted at the 2019 meetings of the Orthopaedic Research Society (ORS) and Osteoarthritis Research Society International (OARSI) that included presentations and questions/comments submitted from leading OA researchers representing imaging, mechanics, biomarkers, phenotyping, clinical, epidemiology, inflammation and exercise.Solutions for OA require a paradigm shift in research and clinical methods in which OA is contextualized as a complex whole-body/person disease. New OA definition(s)/phenotype(s) and OA markers/signals are needed to address the interplay between genetic and environmental factors of the disease as well as capture the mechanosensitivity of the disease. The term "Mechanokines" was proposed to highlight the importance of incorporating whole body mechanics as a marker of early OA. New interventions and apparent paradoxical observations/questions (e.g. exercise vs. load modification) were also discussed in the context of considering OA as a complex system.To advance new OA treatments that are safe and effective, OA should be considered as a "Whole Person" disease. This approach requires a concerted effort to bridge disciplines and include interactions across scales from the molecule to the whole body, including psychosocial aspects.

  View details for DOI 10.1016/j.ocarto.2020.100026

  View details for PubMedID 36474561

  View details for PubMedCentralID PMC9718333

• A Systems View of Risk Factors for Knee Osteoarthritis Reveals Insights into the Pathogenesis of the Disease ANNALS OF BIOMEDICAL ENGINEERING Andriacchi, T. P., Favre, J., Erhart-Hledik, J. C., Chu, C. R. 2015; 43 (2): 376-387

  Abstract

  Early detection of osteoarthritis (OA) remains a critical yet unsolved multifaceted problem. To address the multifaceted nature of OA a systems model was developed to consolidate a number of observations on the biological, mechanical and structural components of OA and identify features common to the primary risk factors for OA (aging, obesity and joint trauma) that are present prior to the development of clinical OA. This analysis supports a unified view of the pathogenesis of OA such that the risk for developing OA emerges when one of the components of the disease (e.g., mechanical) becomes abnormal, and it is the interaction with the other components (e.g., biological and/or structural) that influences the ultimate convergence to cartilage breakdown and progression to clinical OA. The model, applied in a stimulus-response format, demonstrated that a mechanical stimulus at baseline can enhance the sensitivity of a biomarker to predict cartilage thinning in a 5 year follow-up in patients with knee OA. The systems approach provides new insight into the pathogenesis of the disease and offers the basis for developing multidisciplinary studies to address early detection and treatment at a stage in the disease where disease modification has the greatest potential for a successful outcome.

  View details for DOI 10.1007/s10439-014-1117-2

  View details for PubMedID 25224078

• The Nature of In Vivo Mechanical Signals That Influence Cartilage Health and Progression to Knee Osteoarthritis CURRENT RHEUMATOLOGY REPORTS Andriacchi, T. P., Favre, J. 2014; 16 (11)

  Abstract

  Knee osteoarthritis is a disease that can be initiated along multiple pathways that ultimately leads to pain, loss of function and breakdown of the articular cartilage. While the various pathways have biological and structural elements, the mechanical pathways play a critical role in the development of the disease. The forces and motions occurring during ambulation provide mechanical signals sensed at the scale of the cell that are critical to healthy joint homeostasis. As such, ambulatory changes associated with aging, obesity, or joint injury that occur prior to the development of symptoms of OA can ultimately lead to clinical OA. Conversely, inter-scale signaling (e.g., pain) generated by biological changes in the early stages of OA can produce adaptive ambulatory changes that can modify the rate of OA progression. Thus, the nature of the physical and clinical response to the mechanical signals that occur during ambulation is critical to understanding the etiology of osteoarthritis.

  View details for DOI 10.1007/s11926-014-0463-2

  View details for Web of Science ID 000343893800010

  View details for PubMedID 25240686

• OSTEOARTHRITIS Probing knee OA as a system responding to a stimulus NATURE REVIEWS RHEUMATOLOGY Andriacchi, T. P. 2012; 8 (7): 371-372

  View details for DOI 10.1038/nrrheum.2012.59

  View details for Web of Science ID 000305969900001

  View details for PubMedID 22526027

• Differences in tibial rotation during walking in ACL reconstructed and healthy contralateral knees JOURNAL OF BIOMECHANICS Scanlan, S. F., Chaudhari, A. M., Dyrby, C. O., Andriacchi, T. P. 2010; 43 (9): 1817-1822

  Abstract

  This study tested the hypotheses that in patients with a successful anterior cruciate ligament (ACL) reconstruction, the internal-external rotation, varus-valgus, and knee flexion position of reconstructed knees would be different from uninjured contralateral knees during walking. Twenty-six subjects with unilateral ACL reconstructions (avg 31 years, 1.7 m, 68 kg, 15 female, 24 months past reconstruction) and no other history of serious lower limb injury walked at a self-selected speed in the gait laboratory, with the uninjured contralateral knee as a matched control. Kinematic measurements of tibiofemoral motion were made using a previously-described point-cluster technique. Repeated-measures ANOVA (alpha=0.017) was used to compare ACL-reconstructed knees to their contralateral knees at four distinct points during the stance phase of walking. An offset towards external tibial rotation in ACL-reconstructed knees was maintained over all time points (95%CI 2.3+/-1.3 degrees ). Twenty-two out of twenty-six individuals experienced an average external tibial rotation offset throughout stance phase. Varus-valgus rotation and knee flexion were not significantly different between reconstructed and contralateral knees. These findings show that differences in tibial rotation during walking exist in ACL reconstructed knees compared to healthy contralateral knees, providing a potential explanation why these patients are at higher risk of knee osteoarthritis in the long-term.

  View details for DOI 10.1016/j.jbiomech.2010.02.010

  View details for Web of Science ID 000279468500024

  View details for PubMedID 20181339

  View details for PubMedCentralID PMC2882513

• Gait mechanics influence healthy cartilage morphology and osteoarthritis of the knee. journal of bone and joint surgery. American volume Andriacchi, T. P., Koo, S., Scanlan, S. F. 2009; 91: 95-101

  Abstract

  The response of healthy and diseased cartilage of the knee to the mechanics of walking is examined, with the goal of providing insight into the relationship between the kinematics and kinetics of the knee during walking and the maintenance of cartilage health. The combination of information from three-dimensional thickness models of cartilage derived from magnetic resonance imaging and the analysis of the interaction between load at the knee and kinematic changes during walking associated with loss of the anterior cruciate ligament demonstrated the importance of considering walking mechanics as an important factor in the initiation and progression of osteoarthritis. In particular, this material suggests that knee cartilage becomes conditioned to loading and to the large number of repetitive cycles of loading that occur during walking and that healthy cartilage homeostasis is maintained as long as there are no changes to the normal patterns of locomotion, the structure of the knee joint, or cartilage biology. Thus, there is the potential for a degenerative pathway to be initiated when a condition such as anterior cruciate ligament injury causes the repetitive loading during walking to shift to a new location. The sensitivity of cartilage to the kinematic changes is illustrated with the anterior cruciate ligament-deficient knee and the regional variations in cartilage morphology. The material presented here supports the conclusion that individual variations in the range of loading and kinematics at the knee during walking can have a profound influence on the initiation and progression of osteoarthritis of the knee.

  View details for DOI 10.2106/JBJS.H.01408

  View details for PubMedID 19182033

  View details for PubMedCentralID PMC2663350

• A framework for the in vivo pathomechanics of osteoarthritis at the knee ANNALS OF BIOMEDICAL ENGINEERING Andriacchi, T. P., Mundermann, A., Smith, R. L., Alexander, E. J., Dyrby, C. O., Koo, S. 2004; 32 (3): 447-457

  Abstract

  The in vivo pathomechanics of osteoarthritis (OA) at the knee is described in a framework that is based on an analysis of studies describing assays of biomarkers, cartilage morphology, and human function (gait analysis). The framework is divided into an Initiation Phase and a Progression Phase. The Initiation Phase is associated with kinematic changes that shift load bearing to infrequently loaded regions of the cartilage that cannot accommodate the loads. The Progression Phase is defined following cartilage breakdown. During the Progression Phase, the disease progresses more rapidly with increased load. While this framework was developed from an analysis of in vivo pathomechanics, it also explains how the convergence of biological, morphological, and neuromuscular changes to the musculoskeletal system during aging or during menopause lead to the increased rate of idiopathic OA with aging. Understanding the in vivo response of articular cartilage to its physical environment requires an integrated view of the problem that considers functional, anatomical, and biological interactions. The integrated in vivo framework presented here will be helpful for the interpretation of laboratory experiments as well as for the development of new methods for the evaluation of OA at the knee.

  View details for Web of Science ID 000222465100016

  View details for PubMedID 15095819

• Diverse parameters of ambulatory knee moments differ with medial knee osteoarthritis severity and are combinable into a severity index. Frontiers in bioengineering and biotechnology Ulrich, B., Erhart-Hledik, J. C., Asay, J. L., Omoumi, P., Andriacchi, T. P., Jolles, B. M., Favre, J. 2023; 11: 1176471

  Abstract

  Objective: To characterize ambulatory knee moments with respect to medial knee osteoarthritis (OA) severity comprehensively and to assess the possibility of developing a severity index combining knee moment parameters. Methods: Nine parameters (peak amplitudes) commonly used to quantify three-dimensional knee moments during walking were analyzed for 98 individuals (58.7 ± 9.2 years old, 1.69 ± 0.09 m, 76.9 ± 14.5 kg, 56% female), corresponding to three medial knee osteoarthritis severity groups: non-osteoarthritis (n = 22), mild osteoarthritis (n = 38) and severe osteoarthritis (n = 38). Multinomial logistic regression was used to create a severity index. Comparison and regression analyses were performed with respect to disease severity. Results: Six of the nine moment parameters differed statistically significantly among severity groups (p ≤ 0.039) and five reported statistically significant correlation with disease severity (0.23 ≤ |r| ≤ 0.59). The proposed severity index was highly reliable (ICC = 0.96) and statistically significantly different between the three groups (p < 0.001) as well as correlated with disease severity (r = 0.70). Conclusion: While medial knee osteoarthritis research has mostly focused on a few knee moment parameters, this study showed that other parameters differ with disease severity. In particular, it shed light on three parameters frequently disregarded in prior works. Another important finding is the possibility of combining the parameters into a severity index, which opens promising perspectives based on a single figure assessing the knee moments in their entirety. Although the proposed index was shown to be reliable and associated with disease severity, further research will be necessary particularly to assess its validity.

  View details for DOI 10.3389/fbioe.2023.1176471

  View details for PubMedID 37383522

  View details for PubMedCentralID PMC10293674

• Femoral acetabular impingement labral pathology on MRI is correlated with greater hip flexion and decreased abduction in collegiate water polo players: A pilot study. Journal of ISAKOS : joint disorders & orthopaedic sports medicine Hall, K. E., Langner, J., Segovia, N., Schultz, B., Andriacchi, T., Gold, G., Safran, M. R. 2022; 7 (1): 7-12

  Abstract

  Femoroacetabular impingement (FAI) morphology is associated with hip pain and disability. Water polo players utilise the egg beater motion (method of treading water with legs rotating like an "egg beater"), and it is currently unclear what the relationship is between an egg beater and FAI morphology. Our objective was to associate hip range of motion during egg beater motion to MRI findings.Eight National Collegiate Athletic Association (NCAA) Division 1 varsity water polo athletes (5 females and 3 males) were filmed at orthogonal views performing the egg beater motion using two waterproof cameras in synchrony. A model-based image-matching technique was used to determine hip joint angles which were recorded from the software. These athletes also underwent noncontrast MRI scans of both hips using a 3T MRI scanner and completed an 33-item International Hip Outcome Tool (iHOT-33) hip pain outcomes questionnaire. Descriptive statistics are reported as counts and percentages for categorical variables and as means, standard deviations, and a five-number summary for continuous variables. Relationships between the range of motion measures with MRI measures and with iHOT33 scores were analysed using linear regression models. All statistical analyses were completes using a two-sided level of significance of 0.05.The average alpha angles for the right and left hips were 71.80 ±7.50 and 74.10 ±8.40, respectively. There was no statistically significant correlation between hip range of motion in any plane and alpha angle or lateral centre edge angle (CEA) on MRI. The average iHOT33 was 85.9 ± 18.9. Participants who had a labral tear had significantly smaller hip abduction ranges than participants who did not have a labral tear (29° ± 4.1 vs. 35.3° ± 0.6, p = 0.02), and those who had a labral tear had significantly increased hip flexion during egg beater kicking as compared with participants who did not have a labral tear (28.2° ± 6.1 vs. 16.3° ± 4, p = 0.02). There were no differences between right and left alpha angles or between right and left CEA.There were no significant correlations between hip range of motion and alpha angle or CEA, but hips with labral pathology had greater hip flexion and more limited hip abduction ranges.

  View details for DOI 10.1016/j.jisako.2021.10.003

  View details for PubMedID 35543660

• Visualizing PreOsteoarthritis: Integrating MRI UTE-T2* with Mechanics and Biology to Combat Osteoarthritis The 2019 Elizabeth Winston Lanier Kappa Delta Award. Journal of orthopaedic research : official publication of the Orthopaedic Research Society Chu, C. R., Williams, A. A., Erhart-Hledik, J. C., Titchenal, M. R., Qian, Y., Andriacchi, T. P. 2021

  Abstract

  Osteoarthritis (OA) is a leading cause of pain and disability for which disease modifying treatments remain lacking. This is likely because the symptoms and radiographic changes of OA occur after the onset of irreversible changes. Defining and treating earlier disease states are therefore needed to delay or halt OA progression. Taking this concept a step further, study of OA pathogenesis prior to disease onset by characterizing potentially reversible markers of increased OA risk to identify a state of "pre-osteoarthritis (pre-OA)" shifts the paradigm towards OA prevention. The purpose of this review is to summarize the 42 manuscripts comprising the 2019 Kappa Delta Elizabeth Lanier Award where conceptualization of a systems-based definition for "pre-osteoarthritis (pre-OA)" was followed by demonstration of potentially reversible markers of heightened OA risk in patients after anterior cruciate ligament (ACL) injury and reconstruction. In the process, these efforts contributed a new MRI method of ultrashort echo time enhanced (UTE) T2* mapping to visualize joint tissue damage prior to the development of irreversible changes. The studies presented here support a transformative approach to OA that accounts for interactions between mechanical, biological, and structural markers of OA risk to develop and evaluate new treatment strategies to delay or prevent the onset of clinical disease. This body of work was inspired by and performed for patients. Shifting the paradigm from attempting to modify symptomatic radiographic OA towards monitoring and reversing markers of "pre-OA" opens the door for transforming the clinical approach to OA from palliation to prevention. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/jor.25045

  View details for PubMedID 33788306

• Kinematic Comparison between Medially Congruent and Posterior-Stabilized Third-Generation TKA Designs. Journal of functional morphology and kinesiology Ghirardelli, S., Asay, J. L., Leonardi, E. A., Amoroso, T., Andriacchi, T. P., Indelli, P. F. 2021; 6 (1)

  Abstract

  Background: This study compares knee kinematics in two groups of patients who have undergone primary total knee arthroplasty (TKA) using two different modern designs: medially congruent (MC) and posterior-stabilized (PS). The aim of the study is to demonstrate only minimal differences between the groups. Methods: Ten TKA patients (4 PS, 6 MC) with successful clinical outcomes were evaluated through 3D knee kinematics analysis performed using a multicamera optoelectronic system and a force platform. Extracted kinematic data included knee flexion angle at heel-strike (KFH), peak midstance knee flexion angle (MSKFA), maximum and minimum knee adduction angle (KAA), and knee rotational angle at heel-strike. Data were compared with a group of healthy controls. Results: There were no differences in preferred walking speed between MC and PS groups, but we found consistent differences in knee function. At heel-strike, the knee tended to be more flexed in the PS group compared to the MC group; the MSKFA tended to be higher in the PS group compared to the MC group. There was a significant fluctuation in KAA during the swing phase in the PS group compared to the MC group, PS patients showed a higher peak knee flexion moment compared to MC patients, and the PS group had significantly less peak internal rotation moments than the MC group. Conclusions: Modern, third-generation TKA designs failed to reproduce normal knee kinematics. MC knees tended to reproduce a more natural kinematic pattern at heel-strike and during axial rotation, while PS knees showed better kinematics during mid-flexion.

  View details for DOI 10.3390/jfmk6010027

  View details for PubMedID 33804113

• Vertical Ground Reaction Force 2 Years After Anterior Cruciate Ligament Reconstruction Predicts 10-Year Patient-Reported Outcomes. Journal of orthopaedic research : official publication of the Orthopaedic Research Society Erhart-Hledik, J. C., Chu, C. R., Asay, J. L., Mahtani, G. B., Andriacchi, T. P. 2021

  Abstract

  Disruptions in knee biomechanics during walking following anterior cruciate ligament (ACL) injury have been suggested to lead to the development of premature knee osteoarthritis (OA) and to be potential markers of OA risk and targets for intervention. This study investigated if side-to-side differences in early stance peak vertical ground reaction force (vGRF) during walking 2 years after ACL reconstruction are associated with longer-term (10 years post-reconstruction) changes in patient-reported outcomes. Twenty-eight participants (mean age: 28.7±6.4 years) with primary unilateral ACL reconstruction underwent gait analysis for assessment of peak vGRF and completed KOOS and IKDC surveys at 2 years post-surgery (2.2±0.3 years) and completed surveys at follow-up 10 years post-surgery (10.5±0.9 years). Associations between changes (10 year - 2 year) in patient-reported outcomes and between limb-differences in vGRF were assessed with Pearson or Spearman's rho correlation coefficients and exploratory backwards elimination multiple linear regression analyses. Differences in vGRF between symptomatic progressors and non-progressors were also assessed. Side-to-side difference in vGRF was related to the variability in longer-term changes in patient-reported outcome metrics and distinguished symptomatic progressors from non-progressors. Participants with higher vGRF in the ACLR limb versus the contralateral limb had worsening of IKDC (R=-0.391, p=0.040), KOOS Pain (rho=-0.396, p=0.037), KOOS Symptoms (rho=-0.572, p=0.001), and KOOS QOL (R=-0.458, p=0.014) scores at follow-up. Symptomatic progressors had greater vGRF in the ACLR limb as compared to the contralateral limb at baseline than non-progressors (p=0.023). Clinical Relevance: These data highlight associations between a simple-to-measure gait metric and the development of long-term clinical symptoms after ACL injury. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/jor.25025

  View details for PubMedID 33713477

• Longitudinal changes in tibial and femoral cartilage thickness are associated with baseline ambulatory kinetics and cartilage oligomeric matrix protein (COMP) measures in an asymptomatic aging population. Osteoarthritis and cartilage Erhart-Hledik, J. C., Chehab, E. F., Asay, J. L., Favre, J., Chu, C. R., Andriacchi, T. P. 2021

  Abstract

  OBJECTIVE: To address the need for early knee osteoarthritis (OA) markers by testing if longitudinal cartilage thickness changes are associated with specific biomechanical and biological measures acquired at a baseline test in asymptomatic aging subjects.DESIGN: Thirty-eight asymptomatic subjects over age 45 years were studied at baseline and at an average of 7-9 year follow-up. Gait mechanics and knee MRI were measured at baseline and MRI was obtained at follow-up to assess cartilage thickness changes. A subset of the subjects (n=12) also had serum cartilage oligomeric matrix protein measured at baseline in response to a mechanical stimulus (30-minute walk) (mCOMP). Baseline measures, including the knee extension (KEM), flexion (KFM), adduction (KAM) moments and mCOMP, were tested for associations with cartilage thickness changes in specific regions of the knee.RESULTS: Cartilage change in the full medial femoral condyle (p=0.005) and external medial femoral region (p=0.041) was negatively associated with larger early stance peak KEM. Similarly, cartilage change in the full medial femoral region (p=0.009) and medial femoral external region (p=0.043) was negatively associated with larger first peak KAM, while cartilage change in the anterior medial tibia was positively associated with larger first peak KAM (p=0.003). Cartilage change in the anterior medial tibia was also significantly associated (p=0.011) with mCOMP levels 5.5-hours post-activity (percentage of pre-activity levels).CONCLUSIONS: Interactions found between gait, mechanically-stimulated serum biomarkers, and cartilage thickness in an at-risk aging asymptomatic population suggest the opportunity for early detection of OA with new approaches that bridge across disciplines and scales.

  View details for DOI 10.1016/j.joca.2021.02.006

  View details for PubMedID 33610822

• Analyzing Femorotibial Cartilage Thickness Using Anatomically Standardized Maps: Reproducibility and Reference Data. Journal of clinical medicine Favre, J., Babel, H., Cavinato, A., Blazek, K., Jolles, B. M., Andriacchi, T. P. 2021; 10 (3)

  Abstract

  Alterations in cartilage thickness (CTh) are a hallmark of knee osteoarthritis, which remain difficult to characterize at high resolution, even with modern magnetic resonance imaging (MRI), due to a paucity of standardization tools. This study aimed to assess a computational anatomy method producing standardized two-dimensional femorotibial CTh maps. The method was assessed with twenty knees, processed following three common experimental scenarios. Cartilage thickness maps were obtained for the femorotibial cartilages by reconstructing bone and cartilage mesh models in tree-dimension, calculating three-dimensional CTh maps, and anatomically standardizing the maps. The intra-operator accuracy (median (interquartile range, IQR) of -0.006 (0.045) mm), precision (0.152 (0.070) mm), entropy (7.02 (0.71) and agreement (0.975 (0.020))) results suggested that the method is adequate to capture the spatial variations in CTh and compare knees at varying osteoarthritis stages. The lower inter-operator precision (0.496 (0.132) mm) and agreement (0.808 (0.108)) indicate a possible loss of sensitivity to detect differences in a setting with multiple operators. The results confirmed the promising potential of anatomically standardized maps, with the lower inter-operator reproducibility stressing the need to coordinate operators. This study also provided essential reference data and indications for future research using CTh maps.

  View details for DOI 10.3390/jcm10030461

  View details for PubMedID 33530358

• Patient-Reported Outcomes and Knee Mechanics Correlate With Patellofemoral Deep Cartilage UTE-T2* 2 Years After Anterior Cruciate Ligament Reconstruction. The American journal of sports medicine Williams, A. A., Erhart-Hledik, J. C., Asay, J. L., Mahtani, G. B., Titchenal, M. R., Lutz, A. M., Andriacchi, T. P., Chu, C. R. 2021: 363546520982608

  Abstract

  Patellofemoral joint degeneration and dysfunction after anterior cruciate ligament reconstruction (ACLR) are increasingly recognized as contributors to poor clinical outcomes.To determine if greater deep cartilage matrix disruption at 2 years after ACLR, as assessed by elevated patellofemoral magnetic resonance imaging (MRI) ultrashort echo time-enhanced T2* (UTE-T2*), is correlated with (1) worse patient-reported knee function and pain and (2) gait metrics related to patellofemoral tracking and loading, such as greater external rotation of the tibia at heel strike, reduced knee flexion moment (as a surrogate of quadriceps function), and greater knee flexion angle at heel strike.Cross-sectional study; Level of evidence, 3.MRI UTE-T2* relaxation times in patellar and trochlear deep cartilage were compared with patient-reported outcomes and ambulatory gait metrics in 60 patients with ACLR at 2 years after reconstruction. ACLR gait metrics were compared with those of 60 uninjured reference patients matched by age, body mass index, and sex. ACLR UTE-T2* values were compared with those of 20 uninjured reference patients.Higher trochlear UTE-T2* values were associated with worse Knee injury and Osteoarthritis Outcome Scores (KOOS) Sport/Recreation subscale scores (rho = -0.32; P = .015), and showed a trend for association with worse KOOS Pain subscale scores (rho = -0.26; P = .045). At 2 years after ACLR, greater external rotation of the tibia at heel strike was associated with higher patellar UTE-T2* values (R = 0.40; P = .002); greater knee flexion angle at heel strike was associated with higher trochlear UTE-T2* values (rho = 0.39; P = .002); and greater knee flexion moment showed a trend for association with higher trochlear UTE-T2* values (rho = 0.30; P = .019). Patellar cartilage UTE-T2* values, knee flexion angle at heel strike, and external rotation of the tibia at heel strike were all elevated in ACLR knees as compared with reference knees (P = .029, .001, and .044, respectively).Patellofemoral deep cartilage matrix disruption, as assessed by MRI UTE-T2*, was associated with reduced sports and recreational function and with gait metrics reflective of altered patellofemoral loading. As such, the findings provide new mechanistic information important to improving clinical outcomes related to patellofemoral dysfunction after ACLR.

  View details for DOI 10.1177/0363546520982608

  View details for PubMedID 33507800

• Intermittent vibrational stimulation enhances mobility during stair navigation in patients with knee pain. Gait & posture Fischer, A. G., Erhart-Hledik, J. C., Asay, J. L., Andriacchi, T. P. 2021; 86: 125–31

  Abstract

  Reduced quadriceps function and proprioception can cause decreased mobility during stair navigation in patients with knee pain. Patients can benefit from interventions to mitigate pain and restore quadriceps function. Activating the somatosensory system via intermittent vibrational stimulation has the potential to improve stair navigation mobility in patients with knee pain by moderating quadriceps inhibition and enhancing proprioception.What are the effects of intermittent vibrational stimulus synchronized to stair ambulation on muscle activity, kinematics, kinetics, and pain using a randomized controlled clinical trial design.Thirty-eight patients with knee pain were enrolled into a blinded cross-over study, and twenty-nine patients completed all assessments and analyses. Subjects were randomly assigned sequentially to both an active Treatment A (active) and passive Treatment B (passive) worn at the knee during ambulation for 4 weeks with a 2-week washout period between treatments.Knee pain during stair navigation was significantly reduced only with Treatment A (P = 0.007). During ascent, Treatment A (active) significantly increased vastus lateralis activation (P = 0.01), increased knee flexion moment (P = 0.04) and decreased trunk flexion angles (P = 0.015) between baseline and 4-week follow-up. After using passive Treatment B, there were no significant differences in pain (P = 0.19), knee flexion moment (P = 0.09), and trunk flexion angles (P = 0.23). Changes in muscle function correlated significantly with changes in knee flexion moment and trunk flexion with Treatment A (P < 0.015). Descending differed from ascending in response to Treatment A with significantly decreased knee flexion moment(P = 0.04), hip(P = 0.02) and ankle(P = 0.04) flexion angles. Treatment B significantly reduced hip flexion angles (P = 0.005) but not knee flexion moment (P = 0.85).The results of this study suggest that intermittent vibration can improve joint motion and loading during stair navigation by enhancing quadriceps function during stair ascent and improving movement control during stair descent by modifying an adaptive flexed movement pattern in the lower limb.

  View details for DOI 10.1016/j.gaitpost.2021.03.013

  View details for PubMedID 33721689

• New insight on the subchondral bone and cartilage functional unit: Bone mineral density and cartilage thickness are spatially correlated in non-osteoarthritic femoral condyles. Osteoarthritis and cartilage open Babel, H., Omoumi, P., Andriacchi, T. P., Jolles, B. M., Favre, J. 2020; 2 (3): 100079

  Abstract

  This study aimed to improve our understanding of the relationship between bone and cartilage by characterizing the morphological coupling between these mechanosensitive tissues exposed to the same mechanical environment within each knee. Specifically, it reanalyzed a prior dataset to test the hypothesis that the locations of thickest cartilage and densest subchondral bone are correlated in non-osteoarthritic femoral condyles.Anatomically standardized maps of cartilage thickness (CTh) and subchondral bone mineral density (sBMD) were calculated for 50 non-osteoarthritic distal femurs based on computed tomography arthrography examinations. The locations of thickest CTh and densest sBMD were identified in the load-bearing region of the medial and lateral compartments, and correlation analyses were performed to quantify the associations between these locations, with inclusion of age, gender, femoral bone size and femorotibial angle as cofounding variables. Paired Student's t-tests were also performed to compare CTh and sBMD locations.Locations of thickest CTh and densest sBMD were positively correlated along the anteroposterior direction in both compartments (r ≥ 0.45, p ≤ 0.001). Furthermore, thickest CTh was more posterior than densest sBMD in the medial (p = 0.014) and lateral (p < 0.001) compartments, and more lateral than densest sBMD in the lateral compartment (p < 0.001). On average, these location differences were of 1.3, 5.3 and 2.1% of the subchondral bone size.The positive spatial relationship between the locations of thickest CTh and densest sBMD supports the idea of a functional cartilage/subchondral bone unit with morphological coupling conditioned by the individual loading pattern.

  View details for DOI 10.1016/j.ocarto.2020.100079

  View details for PubMedID 36474682

  View details for PubMedCentralID PMC9718193

• Utilizing the somatosensory system via vibratory stimulation to mitigate knee pain during walking: Randomized clinical trial. Gait & posture Fischer, A. G., Erhart-Hledik, J. C., Asay, J. L., Chu, C. R., Andriacchi, T. P. 2020; 80: 37–43

  Abstract

  BACKGROUND: Pain and proprioception deficits are often associated with knee pathologies and resultant quadriceps muscle inhibition. There is a need for new approaches to mitigate active knee pain and restore muscle function during walking. Activating properties of the somatosensory system with common pain and sensory pathways offers a novel opportunity to enhance quadriceps function during walking.RESEARCH QUESTION: Conduct a controlled clinical trial that investigates the effects of applying intermittent vibrational cutaneous stimulation during walking on knee pain and symptoms and their correlations to gait parameters.METHODS: This longitudinal controlled cross-over clinical study included thirty-two patients randomly and blindly assigned to active Treatment A and passive Treatment B for 4 weeks with a 2-week washout period between treatments.RESULTS: Subjects when wearing active Treatment A for 4 weeks had significant (p = 0.04) improvement in patient reported outcomes, while they had no significant differences with passive Treatment B (p > 0.7) compared to the no treatment condition. For Treatment A, subjects with low knee flexion moment and knee flexion angle in no-treatment condition exhibited the greatest increase in knee flexion moment/angle in the active treatment condition (R > 0.57, p < 0.001). These changes in gait measures were correlated significantly to changes in pain.SIGNIFICANCE: This clinical trial indicates that knee pain can be reduced, and gait improved in a manner that enhances quadriceps function by applying intermittent cutaneous stimulation during gait in patients following knee injury or disease. The correlation between decreased pain and improved gait suggests that rehabilitation and exercise therapy may benefit from this treatment.

  View details for DOI 10.1016/j.gaitpost.2020.05.030

  View details for PubMedID 32485422

• TRUNK MOVEMENT PATTERNS ARE ASSOCIATED WITH KNEE FLEXION MOMENT CHANGES WHILE UTILIZING THE SOMATOSENSORY SYSTEM DURING STAIR CLIMBING: CLINICAL TRIAL CROSSOVER STUDY Fischer, A. G., Erhart-Hledik, J. C., Asay, J. L., Chu, C. R., Andriacchi, T. P. ELSEVIER SCI LTD. 2020: S234–S235

  View details for Web of Science ID 000527813600365

• SIDE-TO-SIDE DIFFERENCES IN VERTICAL GROUND REACTION FORCE TWO YEARS AFTER ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION PREDICT LONGITUDINAL CHANGES IN PATIENT-REPORTED OUTCOMES Erhart-Hledik, J., Chu, C., Asay, J., Mahtani, G., Andriacchi, T. ELSEVIER SCI LTD. 2020: S225–S226

  View details for Web of Science ID 000527813600354

• VARIABLE RESPONSES IN PAIN AND FUNCTION 1 MONTH AFTER PLATELET-RICH PLASMA INJECTION ARE RELATED TO CHANGES IN JOINT LOADING DURING GAIT Erhart-Hledik, J., Mahtani, G., Asay, J., Burt, H., Nguyen, M., Do, B., Andriacchi, T., Chu, C. ELSEVIER SCI LTD. 2020: S246–S247

  View details for Web of Science ID 000527813600380

• Changes in Knee Adduction Moment Wearing a Variable-Stiffness Shoe Correlate with Changes in Pain and Mechanically-Stimulated Cartilage Oligomeric Matrix Levels. Journal of orthopaedic research : official publication of the Orthopaedic Research Society Erhart-Hledik, J. C., Mahtani, G. B., Asay, J. L., Migliore, E. n., Nguyen, M. M., Andriacchi, T. P., Chu, C. R. 2020

  Abstract

  This study aimed to determine if changes in knee adduction moment (KAM) after 6 months of variable-stiffness shoe wear are associated with changes in symptoms or serum levels of cartilage oligomeric matrix protein (COMP) following a mechanical stimulus in subjects with medial knee osteoarthritis. Twenty-five subjects were enrolled in the study and assigned a variable-stiffness shoe, and 19 subjects completed 6-month follow-up. At baseline and follow-up subjects underwent gait analysis in control and variable-stiffness shoes, completed Western Ontario and McMaster Universities (WOMAC) questionnaires, and serum COMP concentrations were measured immediately before, 3.5-hours, and 5.5-hours after a 30-minute walking activity. Relationships between changes in KAM (first peak and impulse) and changes in (1) COMP levels in response to the 30-minute walking activity and (2) WOMAC scores from baseline to 6-month follow-up were assessed by Pearson correlation coefficients. Changes in first peak KAM were associated with changes in COMP levels 5.5-hours post-activity from baseline to follow-up (R=0.564, p=0.045). Subjects with greater reductions in KAM had larger decreases in COMP (expressed as a percent of pre-activity levels) at follow-up. Subjects with greater reductions in KAM impulse had significantly greater improvements in WOMAC Pain (R=-0.56, P=0.015) and Function (R=-0.52, P=0.028) scores at follow-up. The study results demonstrated the magnitude of reduction in the KAM wearing a variable-stiffness shoe is associated with decreases in mechanically-stimulated COMP levels and pain/function. This work suggests that interactions between COMP and joint loading during walking should be further investigated in future studies of treatment outcomes in osteoarthritis. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/jor.24770

  View details for PubMedID 32497304

• Longitudinal Changes in the Total Knee Joint Moment After Anterior Cruciate Ligament Reconstruction Correlate With Cartilage Thickness Changes JOURNAL OF ORTHOPAEDIC RESEARCH Erhart-Hledik, J., Chu, C., Asay, J., Favre, J., Andriacchi, T. 2019; 37 (7): 1546–54

  View details for DOI 10.1002/jor.24295

  View details for Web of Science ID 000472548600009

• Longitudinal changes in the total knee joint moment after anterior cruciate ligament reconstruction correlate with cartilage thickness changes. Journal of orthopaedic research : official publication of the Orthopaedic Research Society Erhart-Hledik, J. C., Chu, C. R., Asay, J. L., Favre, J., Andriacchi, T. P. 2019

  Abstract

  This study investigated associations between changes in the total joint moment (TJM) at the knee and changes in cartilage thickness after anterior cruciate ligament reconstruction (ACLR). Seventeen subjects (5 males; age: 29.6±7.3yrs) with unilateral ACLR underwent gait analysis and MRI at baseline (2.2±0.3yrs post-ACLR) and at long-term follow-up (7.7±0.7yrs post-ACLR). Knee loading was assessed using the TJM, and differences in loading were analyzed using repeated measures ANOVA. Pearson correlation coefficients assessed associations between changes in TJM and changes in (medial-to-lateral) M/L femoral cartilage thickness ratios in the ACLR limb. Bilaterally there was no significant change in the magnitude of the TJM first peak (TJM1), however, there was a significant increase in percent contribution of the knee flexion moment (KFM) (p<0.001) and decrease in percent contribution of the knee adduction moment (KAM) to TJM1 (p<0.001). The change in percent contributions of KFM and KAM to TJM1 were associated with changes in M/L femoral cartilage thickness in the ACLR limb. Specifically, subjects with smaller increases in KFM contribution (R=0.521, p=0.032) and smaller decreases in KAM contribution (R=-0.521, p=0.032) had a reduction in M/L ratio in the central femoral sub-region over the follow-up period, with similar trends in the external femoral sub-region. The study results provide new insight into changes in the loading environment at the knee joint prospectively following ACL reconstruction and give evidence that there are modifiable gait metrics that are associated with cartilage changes after ACLR. This article is protected by copyright. All rights reserved.

  View details for PubMedID 30977551

• ACTIVATING THE SOMATOSENSORY SYSTEM ENHANCES KNEE FLEXION AND QUADRICEPS ACTIVITY DURING GAIT AND STAIR CLIMBING Fischer, A. G., Erhart-Hledik, J. C., Asay, J. L., Chu, C. R., Andriacchi, T. P. ELSEVIER SCI LTD. 2019: S63–S64

  View details for Web of Science ID 000466779300085

• CHANGES IN KNEE ADDUCTION MOMENT WITH A VARIABLE-STIFFNESS SHOE ARE RELATED TO CHANGES IN PAIN AND FUNCTION Erhart-Hledik, J., Mahtani, G., Asay, J., Andriacchi, T., Chu, C. ELSEVIER SCI LTD. 2019: S111–S112

  View details for DOI 10.1016/j.joca.2019.02.167

  View details for Web of Science ID 000466779300161

• Changes in stair ascent biomechanics two to eight years after ACL reconstruction are associated with patient-reported outcomes GAIT & POSTURE Fischer, A. G., Erhart-Hledik, J. C., Chu, C. R., Asay, J. L., Andriacchi, T. P. 2019; 69: 91–95

  View details for DOI 10.1016/j.gaitpost.2019.01.029

  View details for Web of Science ID 000471170900014

• Changes in stair ascent biomechanics two to eight years after ACL reconstruction are associated with patient-reported outcomes. Gait & posture Fischer, A. G., Erhart-Hledik, J. C., Chu, C. R., Asay, J. L., Andriacchi, T. P. 2019; 69: 91–95

  Abstract

  BACKGROUND: Anterior cruciate ligament (ACL) injury is often followed by quadriceps deficits that are apparent with gait analysis. The deficit frequently remains after ACL reconstruction (ACLR). As such, evaluation of ACLR patients could be enhanced by a simple method to detect quadriceps deficits. Analyzing forward trunk flexion during stair ascent has been suggested as an assessment of quadriceps function that can be visualized with relatively simple instrumentation.AIM: The purpose of this study was to determine if trunk flexion angle (TFA) during stair ascent is associated with quadriceps function (as measured by the peak knee flexion moment (KFM)) at 2 and 8years post-ACLR and if changes are associated with patient-reported outcomes (PRO).METHODS: Fourteen subjects with unilateral primary ACLR performed three stair-ascending trials at two-time periods: 2 years (baseline) and 8 years (follow-up) post-ACLR. Paired Student t-tests determined differences in KFM and TFA. Associations between KFM, TFA, and PRO were determined through Pearson correlations.RESULTS: Peak KFM during stair ascent significantly increased from baseline to follow-up (p=0.01). Though there was no significant difference in TFA (p=0.84) compared to baseline, 50% of subjects showed decreases in TFA. Further, subjects with reduced TFA during stair ascent at follow-up had significantly increased peak KFM (p=0.029) and improvements in PRO (p=0.001).DISCUSSION: The results suggest that TFA during stair ascent can provide a simple method to assess changes in quadriceps function and pain over time following ACLR. Further analysis is needed to draw conclusions between knee osteoarthritis development and increases in TFA.

  View details for PubMedID 30685631

• Establishing outcome measures in early knee osteoarthritis. Nature reviews. Rheumatology Emery, C. A., Whittaker, J. L., Mahmoudian, A. n., Lohmander, L. S., Roos, E. M., Bennell, K. L., Toomey, C. M., Reimer, R. A., Thompson, D. n., Ronsky, J. L., Kuntze, G. n., Lloyd, D. G., Andriacchi, T. n., Englund, M. n., Kraus, V. B., Losina, E. n., Bierma-Zeinstra, S. n., Runhaar, J. n., Peat, G. n., Luyten, F. P., Snyder-Mackler, L. n., Risberg, M. A., Mobasheri, A. n., Guermazi, A. n., Hunter, D. J., Arden, N. K. 2019

  Abstract

  The classification and monitoring of individuals with early knee osteoarthritis (OA) are important considerations for the design and evaluation of therapeutic interventions and require the identification of appropriate outcome measures. Potential outcome domains to assess for early OA include patient-reported outcomes (such as pain, function and quality of life), features of clinical examination (such as joint line tenderness and crepitus), objective measures of physical function, levels of physical activity, features of imaging modalities (such as of magnetic resonance imaging) and biochemical markers in body fluid. Patient characteristics such as adiposity and biomechanics of the knee could also have relevance to the assessment of early OA. Importantly, research is needed to enable the selection of outcome measures that are feasible, reliable and validated in individuals at risk of knee OA or with early knee OA. In this Perspectives article, potential outcome measures for early symptomatic knee OA are discussed, including those measures that could be of use in clinical practice and/or the research setting.

  View details for DOI 10.1038/s41584-019-0237-3

  View details for PubMedID 31201386

• Modeling knee osteoarthritis pathophysiology using an integrated joint system (IJS): a systematic review of relationships among cartilage thickness, gait mechanics, and subchondral bone mineral density OSTEOARTHRITIS AND CARTILAGE Edd, S. N., Omoumi, P., Andriacchi, T. P., Jolles, B. M., Favre, J. 2018; 26 (11): 1425–37

  Abstract

  To introduce an integrated joint system (IJS) model of joint health and osteoarthritis (OA) pathophysiology through a systematic review of the cross-sectional relationships among three knee properties (cartilage thickness, gait mechanics, and subchondral bone mineral density).Searches using keywords associated with the three knee properties of interest were performed in PubMed, Scopus, and Ovid databases. English-language articles reporting cross-sectional correlations between at least two knee properties in healthy or tibiofemoral OA human knees were included. A narrative synthesis of the data was conducted.Of the 5600 retrieved articles, 13 were included, eight of which reported relationships between cartilage thickness and gait mechanics. The 744 tested knees were separated into three categories based on knee health: 199 healthy, 340 at-risk/early OA, and 205 late OA knees. Correlations between knee adduction moment and medial-to-lateral cartilage thickness ratios were generally positive in healthy, inconclusive in at-risk/early OA, and negative in late OA knees. Knee adduction moment was positively correlated with medial-to-lateral tibial subchondral bone mineral density ratios in knees of all health categories. One study reported a positive correlation between lateral tibial subchondral bone mineral density and femoral cartilage thickness in at-risk/early OA knees.The correlations identified between knee properties in this review agreed with the proposed relationship-based IJS model of OA pathophysiology. Accordingly, the IJS model could provide insights into overcoming current barriers to developing disease-modifying treatments by considering multiple aspects of OA disease, aspects that could be assessed simultaneously at an in vivo system level.

  View details for PubMedID 30056214

• Activating the somatosensory system enhances net quadriceps moment during gait. Journal of biomechanics Fischer, A. G., Erhart-Hledik, J. C., Asay, J. L., Chu, C. R., Andriacchi, T. P. 2018

  Abstract

  Quadriceps muscle rehabilitation following knee injury or disease is often hampered by pain, proprioception deficits or instability associated with inhibition of quadriceps activation during walking. The cross-modal plasticity of the somatosensory system with common sensory pathways including pain, pressure and vibration offers a novel opportunity to enhance quadriceps function during walking. This study explores the effectiveness of an active knee brace that used intermittent cutaneous vibration during walking to enhance the peak knee flexion moment (KFM) during early stance phase as a surrogate for net quadriceps moment (balance between knee extensor and flexor muscle moments). The stimulus was turned on prior to heel strike and turned off at mid-stance of the gait cycle. Twenty-one subjects with knee pathologies known to inhibit quadriceps function were tested walking under three conditions: control (no brace), a passive brace, and an active brace. Findings show that compared to the control, subjects wearing an active brace during gait exhibited a significant (p < 0.001) increase in peak KFM and no significant difference when wearing a passive brace (p = 0.17). Furthermore, subjects with low KFM and knee flexion angle (KFA) in control exhibited the greatest increase in KFA at loading response in the active brace condition (R = 0.47, p < 0.05). Intermittent cutaneous stimulation during gait, therefore, provides an efficient method for increasing the KFM in patients with knee pathologies. This study's results suggest that intermittent vibration stimulus can activate the cross-modalities of the somatosensory system in a manner that gates pain stimulus and possibly restores quadriceps function in patients with knee pain.

  View details for PubMedID 30381155

• Changes in the total knee joint moment in patients with medial compartment knee osteoarthritis over 5 years JOURNAL OF ORTHOPAEDIC RESEARCH Asay, J. L., Erhart-Hledik, J. C., Andriacchi, T. P. 2018; 36 (9): 2373–79

  Abstract

  Progression of medial compartment knee osteoarthritis (OA) has been associated with repetitive mechanical loading during walking, often characterized by the peak knee adduction (KAM) and knee flexion moments (KFM). However, the relative contributions of these components to the knee total joint moment (TJM) can change as the disease progresses since KAM and KFM are influenced by different factors that change over time. This study tested the hypothesis that the relative contributions of KAM, KFM, and the rotational moment (KRM) to the TJM change over time in subjects with medial compartment knee OA. Patients with medial compartment knee OA (n = 19) were tested walking at their self-selected speed at baseline and a 5-year follow-up. For each frame during stance, the TJM was calculated using the KAM, KFM, and KRM. The peaks of the TJM and the relative contributions of the moment components at the time of the peaks of the TJM were tested for changes between baseline and follow-up. The percent contribution of KFM to the first peak of the TJM (TJM1) significantly decreased (p < 0.001) and the percent contribution of KAM to TJM1 significantly increased (p < 0.001), while the magnitude of the TJM1 did not significantly change over the 5-year follow-up. These gait changes with disease progression appear to maintain a constant TJM1, but the transition from a KFM to a KAM dominance appears to reflect gait changes associated with progressing OA and pain. Thus, the TJM and its component analysis captures a comprehensive metric for total loading on the knee over time. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

  View details for PubMedID 29611879

• Sensitivity of serum concentration of cartilage biomarkers to 21-days of bed rest JOURNAL OF ORTHOPAEDIC RESEARCH Liphardt, A., Mundermann, A., Andriacchi, T. P., Achtzehn, S., Heer, M., Mester, J. 2018; 36 (5): 1465–71

  Abstract

  The objective of the study was to test the hypothesis that serum levels of cartilage oligomeric matrix protein (COMP) would decrease and serum levels of tumor-necrosis factor alpha (TNF-α) and selected matrix metalloproteinases (MMPs) would increase in response to bed rest (BR) and that these changes are unaffected by the intake of potassium bicarbonate or whey protein. Seven and nine healthy male subjects participated in two 21-day 6° head down tilt crossover BR-studies with nutrition interventions. Serum samples were taken before, during, and after BR and biomarker concentrations were measured using commercial enzyme-linked immunosorbent assays. MMP-3 during BR was significantly lower than at baseline (reduction greater 20%; p < 0.001). MMP-3 increased significantly from 14 to 21 days of BR (+7%; p = 0.049). COMP during BR was significantly lower than at baseline (reduction greater 20%; p < 0.001). MMP-3 and COMP returned to baseline within 1 day after BR. MMP-9 on day 3 of BR was significantly lower than at baseline (-31%; p < 0.033) and on days 3, 5, and 14 of BR significantly lower than at the end of and after BR (reduction greater 35%; p < 0.030). The nutritional countermeasures did not affect these results. The observed changes in cartilage biomarkers may be caused by altered cartilage metabolism in response to the lack of mechanical stimulus during BR and inflammatory biomarkers may play a role in changes in biomarker levels.Immobilization independently from injury can cause altered cartilage biomarker concentration. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1465-1471, 2018.

  View details for PubMedID 29077223

• Longitudinal changes in knee gait mechanics between 2 and 8 years after anterior cruciate ligament reconstruction. Journal of orthopaedic research : official publication of the Orthopaedic Research Society Erhart-Hledik, J. C., Chu, C. R., Asay, J. L., Andriacchi, T. P. 2018; 36 (5): 1478–86

  Abstract

  The purpose of this study was to longitudinally investigate changes in knee joint kinematics and kinetics from 2 to 8 years post-ACLR. Seventeen subjects with primary unilateral transtibial ACLR performed bilateral gait analysis approximately 2 years and 8 years post-ACLR. Seventeen matched healthy control subjects were also analyzed. Kinematic and kinetic comparisons between the ACLR and contralateral limbs over time were completed using a 2*2 (time, limb) repeated-measures ANOVA. Unpaired Student's t-tests were used to compare the ACLR and contralateral kinematics and kinetics to the control group. The ACLR and contralateral limbs had similar gait changes over time. Kinetic changes over time included a reduction in first (p=0.048) and second (p<0.001) peak extension moments, internal rotation moment (p<0.001), adduction moment (first peak: p=0.002, second peak: p=0.009, impulse: p=0.004) and an increase in peak knee flexion moment (p=0.002). Kinematic changes over time included increases in peak knee flexion angle in the first half of stance (p=0.026), minimum knee flexion angle in the second half of stance (p<0.001), and average external rotation angle during stance (p=0.007), and a reduction in average anterior femoral displacement during stance (p=0.006). Comparison to healthy controls demonstrated improvement in some gait metrics over time. The results demonstrated longitudinal changes from 2 to 8 years after ACLR in knee joint kinetics and kinematics that have been related to clinical outcome after ACLR and the progression of knee OA, and support future larger and comprehensive investigations into long-term changes in joint mechanics in the ACLR population. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1478-1486, 2018.

  View details for PubMedID 28984381

• ACTIVE FEEDBACK GAIT RETRAINING ALTERS FOOT PRESSURE PATTERNS AND REDUCES KNEE ADDUCTION MOMENT IN AN ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTED POPULATION Erhart-Hledik, J. C., Mahtani, G. B., Asay, J. L., Chu, C. R., Andriacchi, T. P. ELSEVIER SCI LTD. 2018: S364

  View details for Web of Science ID 000432189700711

• MECHANICALLY STIMULATED CS846 CORRELATES WITH ULTRASHORT ECHO TIME ENHANCED T2*QUANTITATIVE MRI AND GAIT MECHANICS 2 YEARS AFTER ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION Titchenal, M. R., Williams, A. A., Asay, J. L., Migliore, E., Erhart-Hledik, J. C., Andriacchi, T. P., Chu, C. R. ELSEVIER SCI LTD. 2018: S176–S177

  View details for Web of Science ID 000432189700374

• MRI UTE-T2*profile characteristics correlate to walking mechanics and patient reported outcomes 2 years after ACL reconstruction OSTEOARTHRITIS AND CARTILAGE Williams, A. A., Titchenal, M. R., Andriacchi, T. P., Chu, C. R. 2018; 26 (4): 569–79

  Abstract

  Quantitative magnetic resonance imaging (MRI) ultrashort echo time (UTE) T2* is sensitive to cartilage deep tissue matrix changes after anterior cruciate ligament reconstruction (ACLR). This study was performed to determine whether UTE-T2* profile analysis is a useful clinical metric for assessing cartilage matrix degeneration. This work tests the hypotheses that UTE-T2* depthwise rates of change (profile slopes) correlate with clinical outcome metrics of walking mechanics and patient reported outcomes (PRO) in patients 2 years after ACLR.Thirty-six patients 2 years after ACLR completed knee MRI, gait analysis, and PRO. UTE-T2* maps were generated from MRI images and depthwise UTE-T2* profiles were calculated for weight-bearing cartilage in the medial compartment. UTE-T2* profiles from 14 uninjured subjects provided reference values. UTE-T2* profile characteristics, including several different measures of profile slope, were tested for correlation to kinetic and kinematic measures of gait and also to PRO.Decreasing UTE-T2* profile slopes in ACLR knees moderately correlated with increasing knee adduction moments (r = 0.41, P < 0.015), greater external tibial rotation (r = 0.44, P = 0.007), and moderately negatively correlated with PRO (r = -0.36, P = 0.032). UTE-T2* profiles from both ACLR and contralateral knees of ACLR subjects differed from that of uninjured controls (P < 0.015).The results of this study suggest that decreasing UTE-T2* profile slopes reflect cartilage deep tissue collagen matrix disruption in a population at increased risk for knee osteoarthritis (OA). That UTE-T2* profiles were associated with mechanical and patient reported measures of clinical outcomes support further study into a potential mechanistic relationship between these factors and OA development.

  View details for PubMedID 29426012

• Cartilage Subsurface Changes to Magnetic Resonance Imaging UTE-T2*2 Years After Anterior Cruciate Ligament Reconstruction Correlate With Walking Mechanics Associated With Knee Osteoarthritis AMERICAN JOURNAL OF SPORTS MEDICINE Titchenal, M. R., Williams, A. A., Chehab, E. F., Asay, J. L., Dragoo, J. L., Gold, G. E., McAdams, T. R., Andriacchi, T. P., Chu, C. R. 2018; 46 (3): 565–72

  Abstract

  Anterior cruciate ligament (ACL) injury increases risk for posttraumatic knee osteoarthritis (OA). Quantitative ultrashort echo time enhanced T2* (UTE-T2*) mapping shows promise for early detection of potentially reversible subsurface cartilage abnormalities after ACL reconstruction (ACLR) but needs further validation against established clinical metrics of OA risk such as knee adduction moment (KAM) and mechanical alignment.Elevated UTE-T2* values in medial knee cartilage 2 years after ACLR correlate with varus alignment and higher KAM during walking.Cohort study (diagnosis); Level of evidence, 2.Twenty patients (mean age, 33.1 ± 10.5 years; 11 female) 2 years after ACLR underwent 3.0-T knee magnetic resonance imaging (MRI), radiography, and gait analysis, after which mechanical alignment was measured, KAM during walking was calculated, and UTE-T2* maps were generated. The mechanical axis and the first and second peaks of KAM (KAM1 and KAM2, respectively) were tested using linear regressions for correlations with deep UTE-T2* values in the central and posterior medial femoral condyle (cMFC and pMFC, respectively) and central medial tibial plateau (cMTP). UTE-T2* values from ACL-reconstructed patients were additionally compared with those of 14 uninjured participants (mean age, 30.9 ± 8.9 years; 6 female) using Mann-Whitney U and standard t tests.Central weightbearing medial compartment cartilage of ACL-reconstructed knees was intact on morphological MRI. Mean UTE-T2* values were elevated in both the cMFC and pMFC of ACL-reconstructed knees compared with those of uninjured knees ( P = .003 and P = .012, respectively). In ACL-reconstructed knees, UTE-T2* values of cMFC cartilage positively correlated with increasing varus alignment ( R = 0.568). Higher UTE-T2* values in cMFC and cMTP cartilage of ACL-reconstructed knees also correlated with greater KAM1 ( R = 0.452 and R = 0.463, respectively) and KAM2 ( R = 0.465 and R = 0.764, respectively) and with KAM2 in pMFC cartilage ( R = 0.602).Elevated deep UTE-T2* values of medial knee cartilage 2 years after ACLR correlate with 2 clinical markers of increased risk of medial knee OA. These results support the clinical utility of MRI UTE-T2* for early diagnosis of subsurface cartilage abnormalities. Longitudinal follow-up of larger cohorts is needed to determine the predictive and staging potential of UTE-T2* for posttraumatic OA.

  View details for PubMedID 29293364

• One year effectiveness of neuromuscular exercise compared with instruction in analgesic use on knee function in patients with early knee osteoarthritis: the EXERPHARMA randomized trial OSTEOARTHRITIS AND CARTILAGE Holsgaard-Larsen, A., Christensen, R., Clausen, B., Sondergaard, J., Andriacchi, T. P., Roos, E. M. 2018; 26 (1): 28–33

  Abstract

  To test long-term effectiveness of neuromuscular exercise (NEMEX) with instructions in optimized pharmacological treatment (PHARMA) on activities of daily living (ADL) in patients with early knee osteoarthritis.12-months follow-up from a randomized controlled trial. Participants with mild-to-moderate medial tibiofemoral knee osteoarthritis were randomly allocated to 8 weeks NEMEX or PHARMA. The primary outcome measure was the ADL-subscale of the Knee Injury and Osteoarthritis Outcome Score (KOOS). Secondary outcome measures included the other four KOOS-subscales, the University of California Activity Score (UCLA) and the European Quality of Life-5 Dimensions.Ninety-three patients (57% women, 58 ± 8 years, body mass index 27 ± 4 kg/m2) were randomized to NEMEX (n = 47) or PHARMA group (n = 46) with data from 85% being available at 12-months follow-up. Good compliance was achieved for 49% of the participants in NEMEX (≥12 sessions) and 7% in PHARMA (half the daily dose of acetaminophen/NSAIDs ≥ 28 days). Within-group improvements in NEMEX were considered to be clinically relevant (≥10 points) for all KOOS-subscales, except Sport/Rec whereas, no between-groups difference in the primary outcome KOOS ADL (3.6 [-2.1 to 9.2]; P = 0.216) was observed. For KOOS Symptoms, a statistically significant difference of 7.6 points (2.6-12.7; P = 0.004) was observed in favor of NEMEX with 47% improving ≥10 points.No difference in improvement in difficulty with ADL was observed. NEMEX improved knee symptoms to a greater extent with half of patients reporting clinically relevant improvements. CLINICALTRIALS.NCT01638962 (July 3, 2012).S-20110153.

  View details for PubMedID 29107059

• Speed, age, sex, and body mass index provide a rigorous basis for comparing the kinematic and kinetic profiles of the lower extremity during walking. Journal of biomechanics Chehab, E. F., Andriacchi, T. P., Favre, J. 2017

  Abstract

  The increased use of gait analysis has raised the need for a better understanding of how walking speed and demographic variations influence asymptomatic gait. Previous analyses mainly reported relationships between subsets of gait features and demographic measures, rendering it difficult to assess whether gait features are affected by walking speed or other demographic measures. The purpose of this study was to conduct a comprehensive analysis of the kinematic and kinetic profiles during ambulation that tests for the effect of walking speed in parallel to the effects of age, sex, and body mass index. This was accomplished by recruiting a population of 121 asymptomatic subjects and analyzing characteristic 3-dimensional kinematic and kinetic features at the ankle, knee, hip, and pelvis during walking trials at slow, normal, and fast speeds. Mixed effects linear regression models were used to identify how each of 78 discrete gait features is affected by variations in walking speed, age, sex, and body mass index. As expected, nearly every feature was associated with variations in walking speed. Several features were also affected by variations in demographic measures, including age affecting sagittal-plane knee kinematics, body mass index affecting sagittal-plane pelvis and hip kinematics, body mass index affecting frontal-plane knee kinematics and kinetics, and sex affecting frontal-plane kinematics at the pelvis, hip, and knee. These results could aid in the design of future studies, as well as clarify how walking speed, age, sex, and body mass index may act as potential confounders in studies with small populations or in populations with insufficient demographic variations for thorough statistical analyses.

  View details for DOI 10.1016/j.jbiomech.2017.04.014

  View details for PubMedID 28501342

• The effect of instruction in analgesic use compared with neuromuscular exercise on knee-joint load in patients with knee osteoarthritis: a randomized, single-blind, controlled trial OSTEOARTHRITIS AND CARTILAGE Holsgaard-Larsen, A., Clausen, B., Sondergaard, J., Christensen, R., Andriacchi, T. P., Roos, E. M. 2017; 25 (4): 470-480

  View details for DOI 10.1016/j.joca.2016.10.022

  View details for Web of Science ID 000401093200010

• Gait mechanics 2 years after anterior cruciate ligament reconstruction are associated with longer-term changes in patient-reported outcomes JOURNAL OF ORTHOPAEDIC RESEARCH Erhart-Hledik, J. C., Chu, C. R., Asay, J. L., Andriacchi, T. P. 2017; 35 (3): 634-640

  Abstract

  This study tested the hypothesis that side-to-side differences in knee gait mechanics 2 years after anterior cruciate ligament (ACL) reconstruction are associated with long-term (∼8 years post-reconstruction) changes in patient-reported outcome scores. Sixteen subjects (5 males; age: 29.1 ± 7.1 years) with primary unilateral ACL reconstruction were gait tested at baseline (2.2 ± 0.3 years post-ACL reconstruction) and filled out KOOS and Lysholm surveys. At long-term follow-up (7.7 ± 0.7 years post-ACL reconstruction), the same subjects completed KOOS and Lysholm surveys. Pearson correlation coefficients assessed relationships between side-to-side differences in kinematics and kinetics at baseline and changes in Lysholm and KOOS Pain/QOL scores from 2 to 8 years post-ACL reconstruction. Significant associations were seen between greater average varus rotation (Lysholm: R = -0.654, p = 0.006) and less anterior femoral displacement (Lysholm: R = 0.578, p = 0.019) during stance of the ACL reconstructed knee versus the contralateral knee at baseline and worse follow-up outcome scores. Significant associations were seen between greater peak knee flexion moment (KOOS Pain: R = -0.572, p = 0.026; KOOS QOL: R = -0.636, p = 0.011), peak knee adduction moment (Lysholm: R = -0.582, p = 0.018; KOOS Pain: R = -0.742, p = 0.002; KOOS QOL: R = -0.551, p = 0.033), and peak internal rotation moment (Lysholm: R = 0.525, p = 0.037; KOOS Pain: R = 0.815, p < 0.001; KOOS QOL: R = 0.777, p = 0.001) in the ACL reconstructed knee at baseline with worse follow-up outcomes. The results of this study support the hypotheses that early changes in gait mechanics following ACL reconstruction are associated with longer-term clinical changes in patient-reported outcomes, suggesting that biomechanical markers obtained as early as 2 years after ACL reconstruction may be useful to understand clinical outcomes in this population. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:634-640, 2017.

  View details for DOI 10.1002/jor.23317

  View details for Web of Science ID 000397594300026

• Early Changes in Knee Center of Rotation During Walking After Anterior Cruciate Ligament Reconstruction Correlate With Later Changes in Patient-Reported Outcomes AMERICAN JOURNAL OF SPORTS MEDICINE Titchenal, M. R., Chu, C. R., Erhart-Hledik, J. C., Andriacchi, T. P. 2017; 45 (4): 915-921

  Abstract

  Altered knee kinematics after anterior cruciate ligament injury and reconstruction (ACLR) have been implicated in the development of posttraumatic osteoarthritis (PTOA), leading to poor long-term clinical outcomes.This study was conducted to determine (1) whether the average knee center of rotation (KCOR), a multidimensional metric of knee kinematics, of the ACL-reconstructed knee during walking differs from that of the uninjured contralateral knee; (2) whether KCOR changes between 2 and 4 years after surgery; and (3) whether early KCOR changes predict patient-reported outcomes 8 years after ACLR.Descriptive laboratory study.Twenty-six human participants underwent gait analysis with calculation of bilateral KCOR during walking at 2 and 4 years after unilateral ACLR. Knee injury and Osteoarthritis Outcome Score (KOOS) and Lysholm score results were collected at 2, 4, and 8 years after ACLR in 13 of these participants.The ACL-reconstructed knee showed greater medial compartment motion because of pivoting about a more lateral KCOR ( P = .03) than the contralateral knee at 2 years. KCOR became less lateral over time ( P = .047), with values approaching those of the uninjured knee by 4 years ( P = .55). KCOR was also more anterior in the ACL-reconstructed knee at 2 years ( P = .02). Between 2 and 4 years, KCOR moved posteriorly in 16 (62%) and anteriorly in 10 (38%) participants. Increasing the anterior position of KCOR in the ACL-reconstructed knee from 2 to 4 years correlated with worsening clinical outcomes at 4 years (KOOS-Quality of Life, R(2) = 0.172) and more strongly at 8 years (Lysholm score, R(2) = 0.41; KOOS-Pain, R(2) = 0.37; KOOS-Symptoms, R(2) = 0.58; and KOOS-Quality of Life, R(2) = 0.50).The observed changes to KCOR during walking between 2 and 4 years after ACLR show progressive improvement toward kinematic symmetry over the 2-year follow-up. The correlation between increasingly abnormal kinematics and worsening clinical outcomes years later in a subset of participants provides a potential explanation for the incidence of PTOA after ACLR.

  View details for DOI 10.1177/0363546516673835

  View details for Web of Science ID 000397492700021

• Anatomically-standardized maps reveal distinct patterns of cartilage thickness with increasing severity of medial compartment knee osteoarthritis. Journal of orthopaedic research Favre, J., Erhart-Hledik, J. C., Blazek, K., Fasel, B., Gold, G. E., Andriacchi, T. P. 2017

  Abstract

  While cartilage thickness alterations are a central element of knee osteoarthritis (OA), differences among disease stages are still incompletely understood. This study aimed to quantify the spatial-variations in cartilage thickness using anatomically standardized thickness maps and test if there are characteristic patterns in patients with different stages of medial compartment knee OA. Magnetic resonance images were acquired for 75 non-OA and 100 OA knees of varying severities (Kellgren and Lawrence (KL) scores 1-4). Three-dimensional cartilage models were reconstructed and a shape matching technique was applied to convert the models into two-dimensional anatomically standardized thickness maps. Difference thickness maps and statistical parametric mapping were used to compare the four OA and the non-OA subgroups. This analysis showed distinct thickness patterns for each clinical stage that formed a coherent succession from the non-OA to the KL 4 subgroups. Interestingly, the only significant difference for early stage (KL 1) was thicker femoral cartilage. With increase in disease severity, typical patterns developed, including thinner cartilage in the anterior area of the medial condyle (significant for KL 3 and 4) and thicker cartilage in the posterior area of the medial and lateral condyles (significant for all OA subgroups). The tibial patterns mainly consisted of thinner cartilage for both medial and lateral compartments (significant for KL 2-4). Comparing anatomically standardized maps allowed identifying patterns of thickening and thinning over the entire cartilage surface, consequently improving the characterization of thickness differences associated with OA. The results also highlighted the value of anatomically standardized maps to analyze spatial variations in cartilage thickness. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

  View details for DOI 10.1002/jor.23548

  View details for PubMedID 28233332

• Effects of active feedback gait retraining to produce a medial weight transfer at the foot in subjects with symptomatic medial knee osteoarthritis. Journal of orthopaedic research Erhart-Hledik, J. C., Asay, J. L., Clancy, C., Chu, C. R., Andriacchi, T. P. 2017

  Abstract

  This study aimed to determine if active feedback gait retraining to produce a medial weight transfer at the foot significantly reduces the knee adduction moment in subjects with medial compartment knee osteoarthritis. Secondarily, changes in peak knee flexion moment, frontal plane knee and ankle kinematics, and center of pressure were investigated. Ten individuals with medial compartment knee osteoarthritis (9 males; age: 65.3 ± 9.8 years; BMI: 27.8 ± 3.0 kg/m(2) ) were tested at self-selected normal and fast speeds in two conditions: Intervention, with an active feedback device attached to the shoe of their more affected leg, and control, with the device de-activated. Kinematics and kinetics were assessed using a motion capture system and force plate. The first peak, second peak, and impulse of the knee adduction moment were significantly reduced by 6.0%, 13.9%, and 9.2%, respectively, at normal speed, with reductions of 10.7% and 8.6% in first peak and impulse at fast speed, respectively, with the active feedback system, with no significant effect on the peak knee flexion moment. Significant reductions in peak varus knee angle and medialized center of pressure in the first half of stance were observed, with reductions in peak varus knee angle associated with reductions in the knee adduction moment. This study demonstrated that active feedback to produce a medial weight-bearing shift at the foot reduces the peaks and impulse of the knee adduction moment in patients with medial compartment knee osteoarthritis. Future research should determine the long-term effect of the active feedback intervention on joint loading, pain, and function. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

  View details for DOI 10.1002/jor.23527

  View details for PubMedID 28120496

• Altered gait mechanics and elevated serum pro-inflammatory cytokines in asymptomatic patients with MRI evidence of knee cartilage loss. Osteoarthritis and cartilage Edd, S. N., Favre, J., Blazek, K., Omoumi, P., Asay, J. L., Andriacchi, T. P. 2017

  Abstract

  To test if sagittal plane gait mechanics parameters and serum inflammation levels differ between healthy asymptomatic subjects and asymptomatic subjects with magnetic resonance imaging (MRI) evidence of cartilage loss.Gait mechanics and resting serum tumor necrosis factor-α (TNFα) concentrations were measured for two groups of asymptomatic subjects recruited for a previous study: Pre-Osteoarthritis (OA) subjects had MRI evidence of partial- or full-thickness knee cartilage loss in at least one compartment (n = 52 (30 female), 1.7 ± 0.1 m, 85.3 ± 18.9 kg, 44 ± 11 years); Control subjects had no MRI features of cartilage loss, osteophytes, bone marrow lesions, nor meniscal pathology in either knee (n = 26 (13 female), 1.7 ± 0.1 m, 74.6 ± 14.9 kg, 34 ± 10 years). Discrete measures of sagittal plane gait kinematics and kinetics were compared between subject groups and adjusted for age and body mass index (BMI) using analysis of covariance (ANCOVA). Serum TNFα concentrations were compared between groups using bootstrap t-test.The Pre-OA group had less extended knees (P = 0.021) and decreased maximum external knee extension moment (P = 0.0062) in terminal stance during gait, as well as increased resting serum TNFα concentration (P = 0.040) as compared to Control subjects. There were no group differences in heel strike flexion angle (P = 0.14), in maximum knee flexion moment (P = 0.91), nor in first peak knee adduction moment (KAM) (post-hoc analysis, P = 0.39).The finding that asymptomatic subjects with cartilage loss had gait and inflammatory characteristics similar to those previously reported in symptomatic OA patients supports the idea that there are specific mechanical and biological factors that precede the onset of knee pain in the pathogenesis of OA.

  View details for DOI 10.1016/j.joca.2016.12.029

  View details for PubMedID 28064033

• Mechanically stimulated biomarkers signal cartilage changes over 5 years consistent with disease progression in medial knee osteoarthritis patients. Journal of orthopaedic research : official publication of the Orthopaedic Research Society Chu, C. R., Sheth, S. n., Erhart-Hledik, J. C., Do, B. n., Titchenal, M. R., Andriacchi, T. P. 2017

  Abstract

  Using serum biomarkers to assess osteoarthritis (OA) disease state and risks of progression remain challenging. This study tested the hypothesis that changes to serum biomarkers in response to a mechanical stimulus in patients with medial knee OA signal cartilage thickness changes 5 years later. Specifically, serum concentrations of a collagen degradation marker (C1,2C) and a chondroitin sulfate synthesis marker (CS846) were measured 0.5 and 5.5 hours after a 30-min walk in 16 patients. Regional cartilage thickness changes measured from magnetic resonance images obtained at study entry and at 5-year follow-up were tested for correlations with baseline biomarker changes after mechanical stimulus, and for differences between groups stratified based on whether biomarker levels increased or decreased. Results showed that an increase in the degradation biomarker C1,2C correlated with cartilage thinning of the lateral tibia (R = -0.63, p = 0.009), whereas an increase in the synthesis marker CS846 correlated with cartilage thickening of the lateral femur (R = 0.76, p = 0.001). Changes in C1,2C and CS846 were correlated (R(2)  = 0.28, p = 0.037). Subjects with increased C1,2C had greater (p = 0.05) medial tibial cartilage thinning than those with decreased C1,2C. In conclusion, the mechanical stimulus appeared to metabolically link the biomarker responses where biomarker increases signaled more active OA disease states. The findings of medial cartilage thinning for patients with increases in the degradation marker and correlation of cartilage thickening in the less involved lateral femur with increases in the synthetic marker were consistent with progression of medial compartment OA. Thus, the mechanical stimulus facilitated assessing OA disease states using serum biomarkers. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

  View details for PubMedID 28862360

• The Nature of Age-Related Differences in Knee Function during Walking: Implication for the Development of Knee Osteoarthritis PLOS ONE Boyer, K. A., Andriacchi, T. P. 2016; 11 (12)

  Abstract

  Changes in knee kinematics have been identified in the early stages of osteoarthritis (OA). However, there is a paucity of information on the nature of kinematic change that occur with aging prior to the development of OA, This study applied a robust statistical method (Principal Component Analysis) to test the hypothesis that coupling between primary (flexion) and secondary (anterior-posterior translation, internal-external rotation) joint motions in walking would differ for age groupings of healthy subjects.Seventy-four healthy participants divided into three groups with mean ages of 24 ± 2.3 years (younger), 48 ± 4.7years (middle-age) and 64 ± 2.4 years (older) were examined. Principal Component Analysis was used to characterize and statistically compare the patterns of knee joint movement and their relationships in walking.There were significant differences between the younger group and both the middle-age and older groups in the knee frontal plane angle and the coupling between knee flexion (PC1, p≤0.04) and the relative magnitudes of secondary plane motions in early and late stance (PC3, p<0.01). Two additional principal components (PC2, p = 0.03 and PC5, p<0.01) described differences in early stance knee flexion and relationship with secondary plane motion through-out stance for the older compared with middle-age group.It appears there are changes in knee kinematics that occur with aging. The kinematic differences were identified for middle-aged as well as older adults suggesting midlife changes in neuromuscular physiology or behavior may have important consequences. These kinematic measures offer the potential to identify early markers for the risk of developing knee OA with aging.

  View details for DOI 10.1371/journal.pone.0167352

  View details for Web of Science ID 000392754300024

  View details for PubMedID 27973527

  View details for PubMedCentralID PMC5156354

• Early Changes in Knee Center of Rotation During Walking After Anterior Cruciate Ligament Reconstruction Correlate With Later Changes in Patient-Reported Outcomes. American journal of sports medicine Titchenal, M. R., Chu, C. R., Erhart-Hledik, J. C., Andriacchi, T. P. 2016

  Abstract

  Altered knee kinematics after anterior cruciate ligament injury and reconstruction (ACLR) have been implicated in the development of posttraumatic osteoarthritis (PTOA), leading to poor long-term clinical outcomes.This study was conducted to determine (1) whether the average knee center of rotation (KCOR), a multidimensional metric of knee kinematics, of the ACL-reconstructed knee during walking differs from that of the uninjured contralateral knee; (2) whether KCOR changes between 2 and 4 years after surgery; and (3) whether early KCOR changes predict patient-reported outcomes 8 years after ACLR.Descriptive laboratory study.Twenty-six human participants underwent gait analysis with calculation of bilateral KCOR during walking at 2 and 4 years after unilateral ACLR. Knee injury and Osteoarthritis Outcome Score (KOOS) and Lysholm score results were collected at 2, 4, and 8 years after ACLR in 13 of these participants.The ACL-reconstructed knee showed greater medial compartment motion because of pivoting about a more lateral KCOR ( P = .03) than the contralateral knee at 2 years. KCOR became less lateral over time ( P = .047), with values approaching those of the uninjured knee by 4 years ( P = .55). KCOR was also more anterior in the ACL-reconstructed knee at 2 years ( P = .02). Between 2 and 4 years, KCOR moved posteriorly in 16 (62%) and anteriorly in 10 (38%) participants. Increasing the anterior position of KCOR in the ACL-reconstructed knee from 2 to 4 years correlated with worsening clinical outcomes at 4 years (KOOS-Quality of Life, R(2) = 0.172) and more strongly at 8 years (Lysholm score, R(2) = 0.41; KOOS-Pain, R(2) = 0.37; KOOS-Symptoms, R(2) = 0.58; and KOOS-Quality of Life, R(2) = 0.50).The observed changes to KCOR during walking between 2 and 4 years after ACLR show progressive improvement toward kinematic symmetry over the 2-year follow-up. The correlation between increasingly abnormal kinematics and worsening clinical outcomes years later in a subset of participants provides a potential explanation for the incidence of PTOA after ACLR.

  View details for PubMedID 27881382

• The effect of instruction in analgesic use compared with neuromuscular exercise on knee-joint load in patients with knee osteoarthritis: a randomized, single-blind, controlled trial. Osteoarthritis and cartilage Holsgaard-Larsen, A., Clausen, B., Søndergaard, J., Christensen, R., Andriacchi, T. P., Roos, E. M. 2016

  Abstract

  To investigate the effect of a neuro-muscular exercise (NEMEX) therapy program compared with instructions in optimized analgesics and anti-inflammatory drug use (PHARMA), on measures of knee-joint load in people with mild to moderate knee osteoarthritis (OA). We hypothesized that knee joint loading during walking would be reduced by NEMEX and potentially increased by PHARMA.Single-blind, randomized controlled trial (RCT) comparing NEMEX therapy twice a week with PHARMA. Participants with mild-to-moderate medial tibiofemoral knee OA were randomly allocated (1:1) to one of two 8-week treatments. Primary outcome was change in knee load during walking (Knee Index, a composite score from all three planes based on 3D movement analysis) after 8 weeks of intervention. Secondary outcomes were frontal plane peak knee adduction moment (KAM), Knee Injury and Osteoarthritis Outcome Scores (KOOS) and functional performance tests.Ninety three participants (57% women, 58 ± 8 years with a body mass index [BMI] of 27 ± 4 kg/m(2) (mean ± standard deviation [SD])) were randomized to NEMEX group (n = 47) or PHARMA (n = 46); data from 44 (94%) and 41 (89%) participants respectively, were available at follow-up. 49% of the participants in NEMEX and only 7% in PHARMA demonstrated good compliance. We found no difference in the primary outcome as evaluated by the Knee Index -0.07 [-0.17; 0.04] Nm/%BW HT. Secondary outcomes largely supported this finding.We found no difference in the primary outcome; knee joint load change during walking from a NEMEX program vs information on the recommended use of analgesics and anti-inflammatory drugs. ClinicalTrials.gov Identifier: NCT01638962 (July 3, 2012). Ethical Committee: S-20110153.

  View details for DOI 10.1016/j.joca.2016.10.022

  View details for PubMedID 27836677

• General scheme to reduce the knee adduction moment by modifying a combination of gait variables. Journal of orthopaedic research Favre, J., Erhart-Hledik, J. C., Chehab, E. F., Andriacchi, T. P. 2016; 34 (9): 1547-1556

  Abstract

  Reducing the knee adduction moment (KAM) is a promising treatment for medial compartment knee osteoarthritis (OA). Although several gait modifications to lower the KAM have been identified, the potential to combine modifications and individual dose-responses remain unknown. This study hypothesized that: (i) there is a general scheme consisting of modifications in trunk sway, step width, walking speed, and foot progression angle that reduces the KAM; (ii) gait modifications can be combined; and (iii) dose-responses differ among individuals. Walking trials with simultaneous modifications in step width, walking speed, progression angle, and trunk sway were analyzed for 10 healthy subjects. Wider step width, slower speed, toeing-in, and increased trunk sway resulted in reduced first KAM peak, whereas wider step width, faster speed, and increased trunk sway reduced the KAM angular impulse. Individual regressions accurately modeled the amplitude of the KAM variables relative to the amplitude of the gait modification variables, while the dose-responses varied strongly among participants. In conclusion, increasing trunk sway, increasing step width, and toeing-in are three gait modifications that could be combined to reduce KAM variables related to knee OA. Results also indicated that some gait modifications reducing the KAM induced changes in the knee flexion moment possibly indicative of an increase in knee loading. Taken together with the different dose-responses among subjects, this study suggested that gait retraining programs should consider this general scheme of modifications with individualization of the modification amplitudes. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1547-1556, 2016.

  View details for DOI 10.1002/jor.23151

  View details for PubMedID 26744298

• Baseline ambulatory knee kinematics are associated with changes in cartilage thickness in osteoarthritic patients over 5 years JOURNAL OF BIOMECHANICS Favre, J., Erhart-Hledik, J. C., Chehab, E. F., Andriacchi, T. P. 2016; 49 (9): 1859-1864

  Abstract

  Although kinematic alterations during walking have been reported with knee osteoarthritis (OA), there is a paucity of longitudinal data, therefore limiting our understanding of the role of kinematics in OA development. This study tested the hypothesis that less knee extension angle and less posterior displacement of the femur relative to the tibia during the heel-strike portion of the gait cycle are associated with greater loss of medial cartilage thickness during a follow-up period of five years. This study also tested for associations between flexion-extension angle and anterior-posterior displacement during other periods of the gait cycle and 5-year cartilage thinning. 16 subjects with moderate medial knee OA were tested with gait analysis and MRI at baseline and had a follow-up MRI after 5 years. Linear regressions were used to assess the relationship between changes in cartilage thickness and baseline kinematics using Pearson correlation coefficients. Multivariate regressions were also performed to adjust for gender, baseline age, BMI, walking speed, Kellgren/Lawrence grade, and baseline knee pain score. As hypothesized, baseline knee flexion angle and femoral displacement during heel-strike and other gait cycle periods were significantly associated with medial femoral and tibial cartilage thinning at the 5 year follow-up; these associations were strengthened after adjustment for covariates. This study provided new insight into the pathogenesis of knee OA where baseline knee kinematics were associated with longitudinal disease progression. These results could serve as a basis for developing newer gait modification interventions to reduce the risk for developing knee OA.

  View details for DOI 10.1016/j.jbiomech.2016.04.029

  View details for Web of Science ID 000377731200060

  View details for PubMedID 27178021

• Modification of Knee Flexion Angle Has Patient-Specific Effects on Anterior Cruciate Ligament Injury Risk Factors During Jump Landing AMERICAN JOURNAL OF SPORTS MEDICINE Favre, J., Clancy, C., Dowling, A. V., Andriacchi, T. P. 2016; 44 (6): 1540-1546

  Abstract

  The incidence of anterior cruciate ligament (ACL) injuries may be decreased through the use of intervention programs that focus on increasing the knee flexion angle during jump landing, which decreases strain on the ACL.To investigate whether intervention training designed to change the knee flexion angle during landing causes secondary changes in other known measures associated with the risk of ACL injuries and to examine the time points when these secondary measures change.Controlled laboratory study.A total of 39 healthy recreational athletes performed a volleyball block jump task in an instrumented gait laboratory. The participants first completed the jumps without any modification to their normal landing technique. They were then given oral instruction to land softly and to increase their knee flexion angle during landing. Lower body kinematics and kinetics were measured before and after the modification using an optoelectronic motion capture system.The knee flexion angle after the modification significantly increased from 11.2° to 15.2° at initial contact and from 67.8° to 100.7° at maximum flexion, and the time between initial contact and maximum flexion increased from 177.4 to 399.4 milliseconds. The flexion modification produced a substantial reduction in vertical ground-reaction force (243.1 to 187.8 %BW) with a concomitant reduction in the maximum flexion moment. Interestingly, the flexion modification only affected the abduction angle and abduction moment for the group of participants that landed in an initial adducted position before the modification and had no significant effect on the group that landed in an abducted position.Increasing the knee flexion angle during jump landing may be an effective intervention to improve knee biomechanical risk factors associated with an ACL injury. However, the fact that the flexion modification only influenced critical risk factors (the abduction angle and abduction moment) in participants who initially landed in an adducted position suggests that the selection of interventions to prevent ACL injuries should account for patient-specific characteristics.The study helps elucidate how increasing the knee flexion angle affects lower body biomechanics and provided evidence for the need to introduce patient-specific strategies for preventing ACL injuries.

  View details for DOI 10.1177/0363546516634000

  View details for Web of Science ID 000377821700031

  View details for PubMedID 26983457

• Gait mechanics 2 years after anterior cruciate ligament reconstruction are associated with longer-term changes in patient-reported outcomes. Journal of orthopaedic research Erhart-Hledik, J. C., Chu, C. R., Asay, J. L., Andriacchi, T. P. 2016

  Abstract

  This study tested the hypothesis that side-to-side differences in knee gait mechanics 2 years after anterior cruciate ligament (ACL) reconstruction are associated with long-term (∼8 years post-reconstruction) changes in patient-reported outcome scores. Sixteen subjects (5 males; age: 29.1 ± 7.1 years) with primary unilateral ACL reconstruction were gait tested at baseline (2.2 ± 0.3 years post-ACL reconstruction) and filled out KOOS and Lysholm surveys. At long-term follow-up (7.7 ± 0.7 years post-ACL reconstruction), the same subjects completed KOOS and Lysholm surveys. Pearson correlation coefficients assessed relationships between side-to-side differences in kinematics and kinetics at baseline and changes in Lysholm and KOOS Pain/QOL scores from 2 to 8 years post-ACL reconstruction. Significant associations were seen between greater average varus rotation (Lysholm: R = -0.654, p = 0.006) and less anterior femoral displacement (Lysholm: R = 0.578, p = 0.019) during stance of the ACL reconstructed knee versus the contralateral knee at baseline and worse follow-up outcome scores. Significant associations were seen between greater peak knee flexion moment (KOOS Pain: R = -0.572, p = 0.026; KOOS QOL: R = -0.636, p = 0.011), peak knee adduction moment (Lysholm: R = -0.582, p = 0.018; KOOS Pain: R = -0.742, p = 0.002; KOOS QOL: R = -0.551, p = 0.033), and peak internal rotation moment (Lysholm: R = 0.525, p = 0.037; KOOS Pain: R = 0.815, p < 0.001; KOOS QOL: R = 0.777, p = 0.001) in the ACL reconstructed knee at baseline with worse follow-up outcomes. The results of this study support the hypotheses that early changes in gait mechanics following ACL reconstruction are associated with longer-term clinical changes in patient-reported outcomes, suggesting that biomechanical markers obtained as early as 2 years after ACL reconstruction may be useful to understand clinical outcomes in this population. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:634-640, 2017.

  View details for DOI 10.1002/jor.23317

  View details for PubMedID 27238273

• Cartilage Strain Distributions Are Different Under the Same Load in the Central and Peripheral Tibial Plateau Regions. Journal of biomechanical engineering Briant, P., Bevill, S., Andriacchi, T. 2015; 137 (12)

  View details for DOI 10.1115/1.4031849

  View details for PubMedID 26501505

• New insight in the relationship between regional patterns of knee cartilage thickness, osteoarthritis disease severity, and gait mechanics. Journal of biomechanics Erhart-Hledik, J. C., Favre, J., Andriacchi, T. P. 2015; 48 (14): 3868-3875

  View details for DOI 10.1016/j.jbiomech.2015.09.033

  View details for PubMedID 26475218

• Dance between biology, mechanics, and structure: A systems-based approach to developing osteoarthritis prevention strategies JOURNAL OF ORTHOPAEDIC RESEARCH Chu, C. R., Andriacchi, T. P. 2015; 33 (7): 939-947

  Abstract

  Osteoarthritis (OA) is a leading cause of human suffering and disability for which disease-modifying treatments are lacking. OA occurs through complex and dynamic interplays between diverse factors over long periods of time. The traditional research and clinical focus on OA, the end stage disease, obscured understanding pathogenesis prior to reaching a common pathway defined by pain and functional deficits, joint deformity, and radiographic changes. To emphasize disease modification and prevention, we describe a multi-disciplinary systems-based approach encompassing biology, mechanics, and structure to define pre-osteoarthritic disease processes. Central to application of this model is the concept of "pre-osteoarthritis," conditions where clinical OA has not yet developed. Rather, joint homeostasis has been compromised and there are potentially reversible markers for heightened OA risk. Key messages from this perspective are (i) to focus research onto defining pre-OA through identifying and validating biological, mechanical, and imaging markers of OA risk, (ii) to emphasize multi-disciplinary approaches, and (iii) to propose that developing personalized interventions to address reversible markers of OA risk in healthy joints may be the key to prevention. Ultimately, a systems-based analysis of OA pathogenesis shows potential to transform clinical practice by facilitating development and testing of new strategies to prevent or delay the onset of osteoarthritis.

  View details for DOI 10.1002/jor.22817

  View details for PubMedID 25639920

• The role of inflammation in the initiation of osteoarthritis after meniscal damage JOURNAL OF BIOMECHANICS Edd, S. N., Giori, N. J., Andriacchi, T. P. 2015; 48 (8): 1420-1426

  Abstract

  Meniscal damage and meniscectomy lead to subsequent osteoarthritis (OA) of the knee joint through multiple and diverse mechanisms, yet the interaction of these mechanisms remains unknown. Therefore, the aim of this review is to suggest the multi-scale, multi-faceted components involved between meniscal injury or meniscectomy and the initiation of OA. There is evidence of structural, mechanical, and biological changes after meniscal damage, all of which can be greatly affected by the presence of local or systemic inflammation. Meniscal damage or resection causes changes in knee mechanics during walking, resulting in altered cartilage loading. Because cartilage is mechanically sensitive, these loading changes can initiate a catabolic effect, culminating in tissue degeneration. The evidence suggests that the addition of elevated inflammation at the time of meniscal damage or meniscectomy results in an accelerated progression toward cartilage degradation. Initial cartilage degradation produces inflammation and pain in conjunction with structural changes to the joint, thus perpetuating the cycle of altered cartilage loading and subsequent degradation. Furthermore, the inflammation secondary to obesity and aging introduces an increased risk of developing OA following meniscal injury. Therefore, an overall route between meniscal damage or resection and OA is presented here in a manner that considers two distinct pathways; these pathways reflect the absence or presence of conditions that cause elevated inflammation.

  View details for DOI 10.1016/j.jbiomech.2015.02.035

  View details for Web of Science ID 000356120000013

  View details for PubMedID 25798759

• Alterations in Knee Kinematics After Partial Medial Meniscectomy Are Activity Dependent AMERICAN JOURNAL OF SPORTS MEDICINE Edd, S. N., Netravali, N. A., Favre, J., Giori, N. J., Andriacchi, T. P. 2015; 43 (6): 1399-1407

  Abstract

  Alterations in knee kinematics after partial meniscectomy have been linked to the increased risk of osteoarthritis in this population. Understanding differences in kinematics during static versus dynamic activities of increased demand can provide important information regarding the possible underlying mechanisms of these alterations.Differences in the following 2 kinematics measures will increase with activity demand: (1) the offset toward external tibial rotation for the meniscectomized limb compared with the contralateral limb during stance and (2) the difference in knee flexion angle at initial foot contact between the meniscectomized and contralateral limbs.Controlled laboratory study.This study compared side-to-side differences in knee flexion and rotation angles during static and dynamic activities. Thirteen patients (2 female) were tested in a motion capture laboratory at 6 ± 2 months after unilateral, arthroscopic, partial medial meniscectomy during a static reference pose and during 3 dynamic activities: walking, stair ascent, and stair descent.The meniscectomized limb demonstrated more external tibial rotation compared with the contralateral limb during dynamic activities, and there was a trend that this offset increased with activity demand (repeated-measures analysis of variance [ANOVA] for activity, P = .07; mean limb difference: static pose, -0.1° ± 3.3°, P = .5; walking, 1.2° ± 3.8°, P = .1; stair ascent, 2.0° ± 3.2°, P = .02; stair descent, 3.0° ± 3.5°, P = .005). Similarly, the meniscectomized knee was more flexed at initial contact than the contralateral limb during dynamic activities (repeated-measures ANOVA for activity P = .006; mean limb difference: reference pose, 1.0° ± 2.5°, P = .09; walking, 2.0° ± 3.9°, P = .05; stair ascent, 5.9° ± 5.3°, P = .009; stair descent, 3.5° ± 4.0°, P = .004).These results suggest both a structural element and a potential muscular element for the differences in kinematics after partial medial meniscectomy and highlight the importance of challenging the knee with activities of increased demands to detect differences in kinematics from the contralateral limb.With further investigation, these findings could help guide clinical rehabilitation of patients with torn meniscus tissue, especially in the context of the patients' increased risk of joint degeneration.

  View details for DOI 10.1177/0363546515577360

  View details for Web of Science ID 000355379200015

  View details for PubMedID 25828080

• Relationship Between Knee Mechanics and Time Since Injury in ACL-Deficient Knees Without Signs of Osteoarthritis AMERICAN JOURNAL OF SPORTS MEDICINE Zabala, M. E., Favre, J., Andriacchi, T. P. 2015; 43 (5): 1189-1196

  Abstract

  There is increasing evidence that kinematic changes after anterior cruciate ligament (ACL) injury can influence the risk for premature osteoarthritis. However, kinematics can change over time, and the factors influencing those changes remain unknown but potentially important.The purpose of this study was to perform gait analysis on a population of ACL-deficient (ACLD) subjects without knee osteoarthritis after considerable time had elapsed since their injuries. The following hypotheses were tested: (1) ACLD knees will have greater anterior femoral translation, external femoral rotation, and flexion moment as compared with healthy contralateral knees with increased time since injury; (2) side-to-side differences in anterior femoral translation and external femoral rotation are positively associated with side-to-side differences in knee flexion moment.Cross-sectional study; Level of evidence, 3.Nineteen subjects with unilateral ACLD (time since injury, 1-384 months) underwent gait testing. Linear regression testing was performed for significant relationships between side-to-side differences in tibial translation and rotation during stance and the amount of time since injury, as well as the relationship between differences in peak flexion moment and differences in translation and rotation.There was a time dependency in side-to-side differences. Subjects with shorter times since injury had the femur of the ACLD knee more posteriorly translated and internally rotated than the femur of the contralateral knee, and subjects with longer times since injury had the femur of the ACLD knee more anteriorly translated (R2=0.33) and externally rotated (R2=0.53) than the femur of the contralateral knee. Additionally, when the population was stratified into 2 subgroups based on time after injury (short-term: 1.4-18.7 months; long-term: 58-383.5 months), a relationship between side-to-side differences in knee flexion moment and side-to-side differences in knee translation and rotation was found for the long-term subgroup.The results of this study provide an understanding of the relationship between kinematics and kinetics of the ACLD knee and the amount of time since injury. They suggest that elapsed time since injury might be an important factor when the function of ACL-injured knees is interpreted as it relates to osteoarthritis.

  View details for DOI 10.1177/0363546514567296

  View details for Web of Science ID 000353980000026

  View details for PubMedID 25649085

• Effects of high heel wear and increased weight on the knee during walking. Journal of orthopaedic research Titchenal, M. R., Asay, J. L., Favre, J., Andriacchi, T. P., Chu, C. R. 2015; 33 (3): 405-411

  Abstract

  Knee osteoarthritis (OA), a leading cause of disability, is more prevalent in women than men. Wearing high heeled shoes has been implicated as a potential contributing factor for the higher lifetime risk of osteoarthritis in women. This study tests the hypotheses that changes to knee kinematics and kinetics observed during high heeled walking increase in magnitude with increasing heel height and are accentuated by a 20% increase in weight. Fourteen healthy females were tested using marker-based gait analysis in combinations of footwear (flat athletic shoe, 3.8 cm and 8.3 cm heeled shoes) and weight (with and without 20% bodyweight vest). At preferred walking speed, knee flexion angle at heel-strike and midstance increased with increasing heel height and weight. Maximum knee extension moment during loading response decreased with added weight; maximum knee extension moment during terminal stance decreased with heel height; maximum adduction moments increased with heel height. Many of the changes observed with increasing heel height and weight were similar to those seen with aging and OA progression. This suggests that high heel use, especially in combination with additional weight, may contribute to increased OA risk in women. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:???-???, 2015.

  View details for DOI 10.1002/jor.22775

  View details for PubMedID 25532875

• The effect on knee-joint load of instruction in analgesic use compared with neuromuscular exercise in patients with knee osteoarthritis: study protocol for a randomized, single-blind, controlled trial (the EXERPHARMA trial) TRIALS Clausen, B., Holsgaard-Larsen, A., Sondergaard, J., Christensen, R., Andriacchi, T. P., Roos, E. M. 2014; 15

  View details for DOI 10.1186/1745-6215-15-444

  View details for Web of Science ID 000345129100001

• Baseline knee adduction and flexion moments during walking are both associated with 5 year cartilage changes in patients with medial knee osteoarthritis OSTEOARTHRITIS AND CARTILAGE Chehab, E. F., Favre, J., Erhart-Hledik, J. C., Andriacchi, T. P. 2014; 22 (11): 1833-1839

  View details for DOI 10.1016/j.joca.2014.08.009

  View details for Web of Science ID 000344186000009

• Baseline knee adduction and flexion moments during walking are both associated with 5 year cartilage changes in patients with medial knee osteoarthritis. Osteoarthritis and cartilage Chehab, E. F., Favre, J., Erhart-Hledik, J. C., Andriacchi, T. P. 2014; 22 (11): 1833-1839

  Abstract

  To test the hypothesis that knee cartilage changes over 5 years are associated with baseline peak knee adduction moment (KAM) and peak knee flexion moment (KFM) during early stance.Baseline KAM and KFM were measured in sixteen subjects with medial knee osteoarthritis (OA). Regional changes in cartilage thickness and changes in medial-to-lateral thickness ratio were quantified using magnetic resonance imaging (MRI) at baseline and again after 5 years. Multiple regression was used to determine whether baseline measures of KAM and KFM were associated with cartilage changes over 5 years. Associations with baseline pain score, Kellgren-Lawrence (KL) grade, walking speed, age, gender, and body mass index (BMI) were tested one-by-one in the presence of KAM and KFM.Changes over 5 years in femoral medial-to-lateral thickness ratio were associated with baseline KAM, KFM, and pain score (R(2) = 0.60, P = 0.010), and most significantly with KAM (R(2) = 0.33, P = 0.019). Changes in tibial medial-to-lateral thickness ratio were associated with baseline KAM, KFM, and walking speed (R(2) = 0.49, P = 0.039), with KFM driving this association (R(2) = 0.40, P = 0.009). Changes in medial tibial thickness were associated with baseline KAM, KFM, and walking speed (R(2) = 0.49, P = 0.041); KFM also drove this association (R(2) = 0.42, P = 0.006).The findings that the KAM has a greater influence on femoral cartilage change and the KFM has a greater influence on tibial cartilage change provide new insight into the tibiofemoral variations in cartilage changes associated with walking kinetics. These results suggest that both KAM and KFM should be considered when designing disease interventions as well as when assessing the risk for OA progression.

  View details for DOI 10.1016/j.joca.2014.08.009

  View details for PubMedID 25211281

  View details for PubMedCentralID PMC4369510

• The Regional Sensitivity of Chondrocyte Gene Expression to Coactive Mechanical Load and Exogenous TNF-alpha Stimuli JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME Bevill, S. L., Boyer, K. A., Andriacchi, T. P. 2014; 136 (9)

  Abstract

  Both mechanical load and elevated levels of proinflammatory cytokines have been associated with the risk for developing osteoarthritis (OA), yet the potential interaction of these mechanical and biological factors is not well understood. The purpose of this study was to evaluate the response of chondrocytes to the effects of dynamic unconfined compression, TNF-α, and the simultaneous effects of dynamic unconfined compression and TNF-α. The response to these three treatments was markedly different and, taken together, the response in the gene expression of chondrocytes to the different treatment conditions suggest a complex interaction between structure, biology, and mechanical loading.

  View details for DOI 10.1115/1.4027937

  View details for Web of Science ID 000340617700005

  View details for PubMedID 24976081

• Evidence for joint moment asymmetry in healthy populations during gait. Gait & posture Lathrop-Lambach, R. L., Asay, J. L., Jamison, S. T., Pan, X., Schmitt, L. C., Blazek, K., Siston, R. A., Andriacchi, T. P., Chaudhari, A. M. 2014; 40 (4): 526-531

  Abstract

  The purpose of this study was to determine the presence and prevalence of asymmetry in lower extremity joint moments within and across healthy populations during overground walking. Bilateral gait data from several studies performed at two institutions were pooled from 182 healthy, pain-free subjects. Four distinct populations were identified based on age, activity level and body mass index. Mean peak external joint moments were calculated from three to six trials of level overground walking at self-selected speed for each subject. Right and left limb moments were reclassified as "greater" or "lesser" moment for each subject to prevent obscuring absolute asymmetry due to averaging over positive and negative asymmetries across subjects. A clinically relevant asymmetry measure was calculated from the peak joint moments with an initial chosen cutoff value of 10%. Confidence intervals for the proportion of subjects with greater than 10% asymmetry between limbs were estimated based on the binomial distribution. We found a high amount of asymmetry between the limbs in healthy populations. More than half of our overall population exceeded 10% asymmetry in peak hip and knee flexion and adduction moments. Group medians exceeded 10% asymmetry for all variables in all populations. This may have important implications on gait evaluations, particularly clinical evaluations or research studies where asymmetry is used as an outcome. Additional research is necessary to determine acceptable levels of joint moment asymmetry during gait and to determine whether asymmetrical joint moments influence the development of symptomatic pathology or success of lower extremity rehabilitation.

  View details for DOI 10.1016/j.gaitpost.2014.06.010

  View details for PubMedID 25035185

  View details for PubMedCentralID PMC4267535

• Evidence for joint moment asymmetry in healthy populations during gait GAIT & POSTURE Lathrop-Lambach, R. L., Asay, J. L., Jamison, S. T., Pan, X., Schmitt, L. C., Blazek, K., Siston, R. A., Andriacchi, T. P., Chaudhari, A. M. 2014; 40 (4): 526-531

  View details for DOI 10.1016/j.gaitpost.2014.06.010

  View details for Web of Science ID 000342502200009

• Camera Networks for Healthcare, Teleimmersion, and Surveillance COMPUTER Chen, C., Favre, J., Kurillo, G., Andriacchi, T. P., Bajcsy, R., Chellappa, R. 2014; 47 (5): 26-36

  View details for Web of Science ID 000337132300020

• Response to letter to the editor regarding "Application of principal component analysis in clinical gait research". Journal of biomechanics Federolf, P., Boyer, K., Andriacchi, T. 2014; 47 (6): 1555-1556

  View details for DOI 10.1016/j.jbiomech.2014.02.013

  View details for PubMedID 24602290

• Age-related differences in sagittal-plane knee function at heel-strike of walking are increased in osteoarthritic patients. Osteoarthritis and cartilage Favre, J., Erhart-Hledik, J. C., Andriacchi, T. P. 2014; 22 (3): 464-471

  Abstract

  To compare age-related patterns of gait with patterns associated with knee osteoarthritis (OA), the following hypotheses were tested: (H1) The sagittal-plane knee function during walking is different between younger and older asymptomatic subjects; (H2) The age-related differences in H1 are increased in patients with knee OA.Walking trials were collected for 110 participants (1.70 ± 0.09 m, 80 ± 14 kg). There were 29 younger asymptomatic subjects (29 ± 4 years) and 81 older participants (59 ± 9 years), that included 27 asymptomatic subjects and 28 and 26 patients with moderate and severe medial knee OA. Discrete variables characterizing sagittal-plane knee function were compared among the four groups using ANOVAs.During the heel-strike portion of the gait cycle at preferred walking speed, the knee was less extended and the shank less inclined in the three older groups compared to the younger asymptomatic group. There were similar differences between the severe OA group and the older asymptomatic and moderate OA groups. Both OA groups also had the femur less posterior relative to the tibia and smaller extension moment than the younger group. During terminal stance, the severe OA group had the knee less extended and smaller knee extension moment than the younger asymptomatic and older moderate OA groups.The differences in knee function, particularly those during heel-strike which were associated with both age and disease severity, could form a basis for looking at mechanical risk factors for initiation and progression of knee OA on a prospective basis.

  View details for DOI 10.1016/j.joca.2013.12.014

  View details for PubMedID 24445065

• Age and Obesity Alter the Relationship Between Femoral Articular Cartilage Thickness and Ambulatory Loads in Individuals Without Osteoarthritis JOURNAL OF ORTHOPAEDIC RESEARCH Blazek, K., Favre, J., Asay, J., Erhart-Hledik, J., Andriacchi, T. 2014; 32 (3): 394-402

  Abstract

  Articular cartilage is sensitive to mechanical loading, so increased risk of osteoarthritis in older or obese individuals may be linked to changes in the relationship between cartilage properties and extrinsic joint loads. A positive relationship has been reported between ambulatory loads and cartilage thickness in young individuals, but whether this relationship exists in individuals who are older or obese is unknown. This study examined the relationship between femoral cartilage thickness and load, measured by weight × height and the peak adduction moment, in young normal-weight (28 subjects, age: 28.0 ± 3.8 years, BMI: 21.9 ± 1.9 kg/m(2)), middle-aged normal-weight (27 subjects, 47.0 ± 6.5 years, 22.7 ± 1.7 kg/m(2)), young overweight/obese (27 subjects, 28.4 ± 3.6 years, 33.3 ± 4.6 kg/m(2)), and middle-aged overweight/obese (27 subjects, 45.8 ± 7.2 years, 31.9 ± 4.4 kg/m(2)) individuals. On the lateral condyle, cartilage thickness was positively correlated with weight × height for all groups (R(2)  = 0.26-0.20) except the middle-aged overweight/obese. On the medial condyle, weight × height was significantly correlated only in young normal-weight subjects (R(2)  = 0.19), as was the case for the correlation between adduction moment and medial-lateral thickness ratio (R(2)  = 0.20). These results suggest that aging and obesity are both associated with a loss of the positive relationship between cartilage thickness and ambulatory loads, and that the relationship is dependent on the compartment and whether the load is generated by body size or subject-specific gait mechanics.

  View details for DOI 10.1002/jor.22530

  View details for Web of Science ID 000329421500006

  View details for PubMedID 24281940

• Biomechanical analysis of three tennis serve types using a markerless system. British journal of sports medicine Abrams, G. D., Harris, A. H., Andriacchi, T. P., Safran, M. R. 2014; 48 (4): 339-342

  Abstract

  PURPOSE: The tennis serve is commonly associated with musculoskeletal injury. Advanced players are able to hit multiple serve types with different types of spin. No investigation has characterised the kinematics of all three serve types for the upper extremity and back. METHODS: Seven NCAA Division I male tennis players performed three successful flat, kick and slice serves. Serves were recorded using an eight camera markerless motion capture system. Laser scanning was utilised to accurately collect body dimensions and data were computed using inverse kinematic methods. RESULTS: There was no significant difference in maximum back extension angle for the flat, kick or slice serves. The kick serve had a higher force magnitude at the back than the flat and slice as well as larger posteriorly directed shoulder forces. The flat serve had significantly greater maximum shoulder internal rotation velocity versus the slice serve. Force and torque magnitudes at the elbow and wrist were not significantly different between the serves. CONCLUSIONS: The kick serve places higher physical demands on the back and shoulder while the slice serve demonstrated lower overall kinetic forces. This information may have injury prevention and rehabilitation implications.

  View details for DOI 10.1136/bjsports-2012-091371

  View details for PubMedID 22936411

• Biomechanical analysis of three tennis serve types using a markerless system BRITISH JOURNAL OF SPORTS MEDICINE Abrams, G. D., Harris, A. H., Andriacchi, T. P., Safran, M. R. 2014; 48 (4)

  Abstract

  PURPOSE: The tennis serve is commonly associated with musculoskeletal injury. Advanced players are able to hit multiple serve types with different types of spin. No investigation has characterised the kinematics of all three serve types for the upper extremity and back. METHODS: Seven NCAA Division I male tennis players performed three successful flat, kick and slice serves. Serves were recorded using an eight camera markerless motion capture system. Laser scanning was utilised to accurately collect body dimensions and data were computed using inverse kinematic methods. RESULTS: There was no significant difference in maximum back extension angle for the flat, kick or slice serves. The kick serve had a higher force magnitude at the back than the flat and slice as well as larger posteriorly directed shoulder forces. The flat serve had significantly greater maximum shoulder internal rotation velocity versus the slice serve. Force and torque magnitudes at the elbow and wrist were not significantly different between the serves. CONCLUSIONS: The kick serve places higher physical demands on the back and shoulder while the slice serve demonstrated lower overall kinetic forces. This information may have injury prevention and rehabilitation implications.

  View details for DOI 10.1136/bjsports-2012-091371

  View details for Web of Science ID 000331185400013

  View details for PubMedID 22936411

• The in vivo relationship between anterior neutral tibial position and loss of knee extension after transtibial ACL reconstruction KNEE Scanlan, S. F., Donahue, J. P., Andriacchi, T. P. 2014; 21 (1): 74-79

  Abstract

  Restoration of anterior tibial stability while avoiding knee extension deficit are a common goal of anterior cruciate ligament (ACL) reconstruction. However, achieving this goal can be challenging. The purpose of this study was to determine whether side-to-side differences in anterior tibial neutral position and laxity are correlated with knee extension deficit in subjects 2years after ACL reconstruction.In the reconstructed and contralateral knees of 29 subjects with transtibial reconstruction, anterior tibiofemoral neutral position was measured with MRI and three-dimensional modeling techniques; terminal knee extension at heel strike of walking and during a seated knee extension were measured via gait analysis; and anterior laxity was measured using the KT-1000.Knees that approached normal anterior stability and anterior tibial position had increased extension deficit relative to the contralateral knee. On average the reconstructed knee had significantly less (2.1±4.4°) extension during active extension and during heel strike of walking (3.0±4.3º), with increased anterior neutral tibial position (2.5±1.7mm) and anterior laxity (1.8±1.0mm). There was a significant correlation between side-to-side difference in anterior neutral tibial position with both measures of knee extension (walking, r=-0.711, p<0.001); active knee extension, r=-0.544, p=0.002).The results indicate a relationship between the loss of active knee extension and a change in anterior neutral tibial position following non-anatomic transtibial ACL reconstruction. Given the increasing evidence of a link between altered kinematics and premature osteoarthritis, these findings provide important information to improve our understanding of in vivo knee function after ACL reconstruction.

  View details for DOI 10.1016/j.knee.2013.06.003

  View details for PubMedID 23830645

• The effect on knee-joint load of instruction in analgesic use compared with neuromuscular exercise in patients with knee osteoarthritis: study protocol for a randomized, single-blind, controlled trial (the EXERPHARMA trial). Trials Clausen, B., Holsgaard-Larsen, A., Søndergaard, J., Christensen, R., Andriacchi, T. P., Roos, E. M. 2014; 15: 444-?

  Abstract

  Knee osteoarthritis (OA) is a mechanically driven disease, and it is suggested that medial tibiofemoral knee-joint load increases with pharmacologic pain relief, indicating that pharmacologic pain relief may be positively associated with disease progression. Treatment modalities that can both relieve pain and reduce knee-joint load would be preferable. The knee-joint load is influenced by functional alignment of the trunk, pelvis, and lower-limb segments with respect to the knee, as well as the ground-reaction force generated during movement. Neuromuscular exercise can influence knee load and decrease knee pain. It includes exercises to improve balance, muscle activation, functional alignment, and functional knee stability. The primary objective of this randomized controlled trial (RCT) is to investigate the efficacy of a NEuroMuscular EXercise (NEMEX) therapy program, compared with optimized analgesics and antiinflammatory drug use, on the measures of knee-joint load in people with mild to moderate medial tibiofemoral knee osteoarthritis.One hundred men and women with mild to moderate medial knee osteoarthritis will be recruited from general medical practices and randomly allocated (1:1) to one of two 8-week treatments, either (a) NEMEX therapy twice a week or (b) information on the recommended use of analgesics and antiinflammatory drugs (acetaminophen and oral NSAIDs) via a pamphlet and video materials. The primary outcome is change in knee load during walking (the Knee Index, a composite score of the first external peak total reaction moment on the knee joint from all three planes based on 3D movement analysis) after 8 weeks of intervention. Secondary outcomes include changes in the external peak knee-adduction moment and impulse and functional performance measures, in addition to changes in self-reported pain, function, health status, and quality of life.These findings will help determine whether 8 weeks of neuromuscular exercise is superior to optimized use of analgesics and antiinflammatory drugs regarding knee-joint load, pain and physical function in people with mild to moderate knee osteoarthritis.ClinicalTrials.gov Identifier: NCT01638962 (July 3, 2012).

  View details for DOI 10.1186/1745-6215-15-444

  View details for PubMedID 25399048

• Is increased joint loading detrimental to obese patients with knee osteoarthritis? A secondary data analysis from a randomized trial OSTEOARTHRITIS AND CARTILAGE Henriksen, M., Hunter, D. J., Dam, E. B., Messier, S. P., Andriacchi, T. P., Lohmander, L. S., Aaboe, J., Boesen, M., Gudbergsen, H., Bliddal, H., Christensen, R. 2013; 21 (12): 1865-1875

  Abstract

  To investigate whether increased knee joint loading due to improved ambulatory function and walking speed following weight loss achieved over 16 weeks accelerates symptomatic and structural disease progression over a subsequent 1 year weight maintenance period in an obese population with knee osteoarthritis (OA).Data from a prospective study of weight loss in obese patients with knee OA (the CARtilage in obese knee OsteoarThritis (CAROT) study) were used to determine changes in knee joint compressive loadings (model estimated) during walking after a successful 16 week weight loss intervention. The participants were divided into 'Unloaders' (participants that reduced joint loads) and 'Loaders' (participants that increased joint loads). The primary symptomatic outcome was changes in knee symptoms, measured with the Knee injury and Osteoarthritis Outcome Score (KOOS) questionnaire, during a subsequent 52 weeks weight maintenance period. The primary structural outcome was changes in tibiofemoral cartilage loss assessed semi-quantitatively (Boston Leeds Knee Osteoarthritis Score (BLOKS) from MRI after the 52 weight maintenance period.157 participants (82% of the CAROT cohort) with medial and/or lateral knee OA were classified as Unloaders (n = 100) or Loaders (n = 57). The groups showed similar significant changes in symptoms (group difference: -2.4 KOOS points [95% CI -6.8:1.9]) and cartilage loss (group difference: -0.06 BLOKS points [95% CI -0.22:0.11) after 1 year, with no statistically significant differences between Loaders and Unloaders.For obese patients undergoing a significant weight loss, increased knee joint loading for 1 year was not associated with accelerated symptomatic and structural disease progression compared to a similar weight loss group that had reduced ambulatory compressive knee joint loads.NCT00655941.

  View details for DOI 10.1016/j.joca.2013.10.003

  View details for Web of Science ID 000329266700007

  View details for PubMedID 24135273

• Patterns of Femoral Cartilage Thickness are Different in Asymptomatic and Osteoarthritic Knees and Can be Used to Detect Disease-Related Differences Between Samples JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME Favre, J., Scanlan, S. F., Erhart-Hledik, J. C., Blazek, K., Andriacchi, T. P. 2013; 135 (10)

  Abstract

  Measures of mean cartilage thickness over predefined regions in the femoral plate using magnetic resonance imaging have provided important insights into the characteristics of knee osteoarthritis (OA), however, this quantification method suffers from the limited ability to detect OA-related differences between knees and loses potentially important information regarding spatial variations in cartilage thickness. The objectives of this study were to develop a new method for analyzing patterns of femoral cartilage thickness and to test the following hypotheses: (1) asymptomatic knees have similar thickness patterns, (2) thickness patterns differ with knee OA, and (3) thickness patterns are more sensitive than mean thicknesses to differences between OA conditions. Bi-orthogonal thickness patterns were extracted from thickness maps of segmented magnetic resonance images in the medial, lateral, and trochlea compartments. Fifty asymptomatic knees were used to develop the method and establish reference asymptomatic patterns. Another subgroup of 20 asymptomatic knees and three subgroups of 20 OA knees each with a Kellgren/Lawrence grade (KLG) of 1, 2, and 3, respectively, were selected for hypotheses testing. The thickness patterns were similar between asymptomatic knees (coefficient of multiple determination between 0.8 and 0.9). The thickness pattern alterations, i.e., the differences between the thickness patterns of an individual knee and reference asymptomatic thickness patterns, increased with increasing OA severity (Kendall correlation between 0.23 and 0.47) and KLG 2 and 3 knees had significantly larger thickness pattern alterations than asymptomatic knees in the three compartments. On average, the number of significant differences detected between the four subgroups was 4.5 times greater with thickness pattern alterations than mean thicknesses. The increase was particularly marked in the medial compartment, where the number of significant differences between subgroups was 10 times greater with thickness pattern alterations than mean thickness measurements. Asymptomatic knees had characteristic regional thickness patterns and these patterns were different in medial OA knees. Assessing the thickness patterns, which account for the spatial variations in cartilage thickness and capture both cartilage thinning and swelling, could enhance the capacity to detect OA-related differences between knees.

  View details for DOI 10.1115/1.4024629

  View details for Web of Science ID 000326087600002

  View details for PubMedID 23722563

• Application of principal component analysis in clinical gait research: Identification of systematic differences between healthy and medial knee-osteoarthritic gait JOURNAL OF BIOMECHANICS Federolf, P. A., BOYER, K. A., Andriacchi, T. P. 2013; 46 (13): 2173-2178

  Abstract

  For a successful completion of a movement task the motor control system has to observe a multitude of internal constraints that govern the coordination of its segments. The purpose of this study was to apply principal component (PC) analysis to detect differences in the segmental coordination between healthy subjects and patients with medial knee osteoarthritis (OA). It was hypothesized that (1) systematic differences in patterns of whole body movement would be identifiable with this method even in small sample sized groups and that (2) these differences will include compensatory movements in the OA patients in both the lower and upper body segments. Marker positions and ground reaction forces of three gait trials of 5 healthy and 5 OA participants with full body marker sets were analyzed using a principal component analysis. Group differences in the PC-scores were determined for the first 10 PC-vectors and a linear combination of those PC-vectors where differences were found defined a discriminant vector. Projecting the original trials onto this discriminant vector yielded significant group differences (t(d=8)=3.011; p=0.017) with greater upper body movement in patients with knee OA that was correlated with the medial-lateral ground reaction force. These results help to characterize the adaptation of whole-body gait patterns to knee OA in a relatively small population and may provide an improved basis for the development of interventions to modify knee load. The PC-based motion analysis offered a highly sensitive approach to identify characteristic whole body patterns of movement associated with pathological gait.

  View details for DOI 10.1016/j.jbiomech.2013.06.032

  View details for Web of Science ID 000324969500010

  View details for PubMedID 23910389

• Functional testing provides unique insights into the pathomechanics of femoroacetabular impingement and an objective basis for evaluating treatment outcome JOURNAL OF ORTHOPAEDIC RESEARCH Rylander, J., Shu, B., Favre, J., Safran, M., Andriacchi, T. 2013; 31 (9): 1461-1468

  Abstract

  Femoroacetabular impingement (FAI) has been recognized as a significant clinical problem. While hip reshaping surgery for treating FAI has had positive clinical outcomes, there remains a need for objective functional outcomes of FAI treatment. We tested the hypothesis that during walking and stair climbing significant changes in hip kinematics would occur following hip reshaping surgery that indicate restoration of normal function post-operatively. Hip and pelvic kinematics were collected for 17 FAI patients pre- and 1 year post-operatively and compared to 17 healthy matched controls. Prior to surgery, FAI patients had significantly reduced hip internal rotation and hip sagittal plane range of motion during walking (p = 0.01, p < 0.001, respectively) and stair climbing (p = 0.01, p < 0.001, respectively) as compared with controls. Post-operatively, these motions were restored to normal during walking (p = 0.70, p = 0.46, respectively), but remained significantly reduced in the FAI patients during stair climbing (p = 0.03, p < 0.001, respectively). These results have important implications for understanding the functional pathomechanics of FAI and providing an objective basis for evaluating treatment outcome. The stair climbing results indicate that problems still exist in the hip joint for activities requiring higher ranges of hip motion and suggest a basis for exploring future improvements for the treatment of FAI.

  View details for DOI 10.1002/jor.22375

  View details for Web of Science ID 000322005300017

  View details for PubMedID 23625839

• Adduction moment increases with age in healthy obese individuals JOURNAL OF ORTHOPAEDIC RESEARCH Blazek, K., Asay, J. L., Erhart-Hledik, J., Andriacchi, T. 2013; 31 (9): 1414-1422

  Abstract

  There is a need to understand how obesity and aging interact to cause an increased risk of medial knee osteoarthritis (OA). This study tested whether the knee adduction and flexion moments increase with age in healthy normal-weight and obese adults, as well as the mechanism of this increase. We analyzed whether ground reaction force magnitude, knee alignment, step width, toe-out angle, body volume distribution, and limb position (knee position relative to the pelvis center) are associated with the adduction moment and whether these variables also change with age. Ninety-six healthy volunteers (60 normal-weight and 36 obese) were tested using marker-based gait analysis; knee alignment was based on marker positions during quiet standing. Adduction moment increased with age in obese (R(2) = 0.19), but not in normal-weight individuals (R(2) = 0.01); knee flexion moment did not change with age in either group. In the obese, only knee alignment and limb position were related to the adduction moment (R(2) = 0.19 and 0.51), but only limb position changed with age (R(2) = 0.26). The resulting increase in adduction moment suggests greater medial compartment loads, which may combine with elevated levels of inflammation to contribute to the increased risk of medial OA in this population.

  View details for DOI 10.1002/jor.22390

  View details for Web of Science ID 000322005300011

  View details for PubMedID 23737249

• Repeatability of gait analysis for measuring knee osteoarthritis pain in patients with severe chronic pain. Journal of orthopaedic research Asay, J. L., Boyer, K. A., Andriacchi, T. P. 2013; 31 (7): 1007-1012

  Abstract

  Gait measures are receiving increased attention in the evaluation of patients with knee osteoarthritis (OA). Yet, there remains a need to assess variability of gait analysis in patients with knee osteoarthritis over time and how pain affects variation in these gait parameters. The purpose of this study was to determine if important gait parameters, such as the knee adduction moment, knee flexion moment, peak vertical ground reaction force, and speed, were repeatable in patients with mild-to-moderate knee OA over a trial period of 12 weeks. Six patients were enrolled in this cross-over study design after meeting strict inclusion criteria. Gait tests were conducted three times at 4 week intervals and once after the placebo arm of a randomized treatment sequence; each gait test followed a 2-week period of receiving a placebo for a pain modifying drug. Repeatability for each gait variable was found using intraclass correlation coefficients (ICC) with a two-way random model. This study found that the knee adduction moment was repeatable throughout the four gait tests. However, normalized peak vertical ground reaction force and knee flexion moment were not as repeatable, varying with pain. This suggests that these gait outcomes could offer a more objective way to measure a patient's level of pain. © 2012 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 31:1007-1012, 2013.

  View details for DOI 10.1002/jor.22228

  View details for PubMedID 23508626

• The relationship between peak knee extension at heel-strike of walking and the location of thickest femoral cartilage in ACL reconstructed and healthy contralateral knees JOURNAL OF BIOMECHANICS Scanlan, S. F., Favre, J., Andriacchi, T. P. 2013; 46 (5): 849-854

  Abstract

  Reports that knee cartilage health is sensitive to kinematic changes, combined with reports of extension loss following ACL reconstruction, underscores the importance of restoring ambulatory knee extension in the context of preventing premature osteoarthritis. The purpose of this study was to test the relationship between individual variations in peak knee extension at heel-strike of walking and the anterior-posterior location of thickest cartilage in the medial and lateral femoral condyles of healthy contralateral and ACL reconstructed knees. In vivo gait analysis and knee MR images were collected from 29 subjects approximately 2 years after unilateral ACL reconstruction. Knee extension was measured at heel-strike of walking and 3-D femoral cartilage thickness models were reconstructed from MR images. The ACL reconstructed knees had significantly reduced knee extension (-1.5±4.2°) relative to the contralateral knees (-4.6±3.4°) at heel-strike of walking but did not have side-to-side differences in the anterior-posterior location or magnitude of thickest medial and lateral femoral cartilage. The anterior-posterior location of the thickest medial femoral cartilage was correlated with knee extension at heel-strike in both the healthy contralateral (R(2)=0.356, p<0.001) and reconstructed (R(2)=0.234, p=0.008) knees. These results suggest that ACL reconstruction can impair terminal extension at periods of ambulatory loading known to be related to cartilage morphology in healthy joints. The fact that the femoral cartilage thickness distribution had not changed at 2 years post-op, even in the subset of subjects with extension loss, suggests that loads may be shifted to thinner cartilage regions, which could have important implications on long-term joint health.

  View details for DOI 10.1016/j.jbiomech.2012.12.026

  View details for Web of Science ID 000316829700001

  View details for PubMedID 23375789

• Valgus Alignment and Lateral Compartment Knee Osteoarthritis: A Biomechanical Paradox or New Insight Into Knee Osteoarthritis? ARTHRITIS AND RHEUMATISM Andriacchi, T. P. 2013; 65 (2): 310-313

  View details for DOI 10.1002/art.37724

  View details for Web of Science ID 000314169400004

  View details for PubMedID 23203607

• Three-dimensional knee moments of ACL reconstructed and control subjects during gait, stair ascent, and stair descent JOURNAL OF BIOMECHANICS Zabala, M. E., Favre, J., Scanlan, S. F., Donahue, J., Andriacchi, T. P. 2013; 46 (3): 515-520

  Abstract

  Changes in knee mechanics following anterior cruciate ligament reconstruction (ACLR) have been implicated as a contributor to the development of premature osteoarthritis (OA). However, changes in ambulatory loading in this population have not been well documented. While the magnitude of the external knee moment vector is a major factor in loading at the knee, there is not a comprehensive understanding of the changes in the individual components of the vector following ACL reconstruction. The purpose of this study was to test for differences in the three components of the external knee moment during walking and stair locomotion between ACLR, contralateral and healthy control knees. Forty-five ACLR and 45 healthy control subjects were tested during walking, stair ascent and descent. ACLR knees had a lower first peak adduction moment than contralateral knees during all three activities. Similarly, additional cases of significant differences between ACLR and contralateral knees consisted of lower peak moments for the ACLR than the contralateral knees. These differences were due to both ACLR and contralateral knees as the ACLR knees indicated lower and the contralateral knees greater peak moments compared to healthy control knees. The results suggest a compensatory change involving greater loading in the contralateral knee, perhaps due to lower loading of the ACLR knee. Further, lower knee moments of the ACLR knee suggest that increased joint loading may not be the initiating factor in the development of OA following ACL reconstruction; but rather previous described kinematic or biological changes might initiate the pathway to knee OA.

  View details for DOI 10.1016/j.jbiomech.2012.10.010

  View details for PubMedID 23141637

• A relationship between mechanically-induced changes in serum cartilage oligomeric matrix protein (COMP) and changes in cartilage thickness after 5 years OSTEOARTHRITIS AND CARTILAGE Erhart-Hledik, J. C., Favre, J., Asay, J. L., Smith, R. L., Giori, N. J., Muendermann, A., Andriacchi, T. P. 2012; 20 (11): 1309-1315

  Abstract

  To evaluate the hypothesis that a mechanical stimulus (30-min walk) will produce a change in serum concentrations of cartilage oligomeric matrix protein (COMP) that is associated with cartilage thickness changes on magnetic resonance imaging (MRI).Serum COMP concentrations were measured by enzyme-linked immunosorbent assay in 17 patients (11 females, age: 59.0±9.2 years) with medial compartment knee osteoarthritis (OA) at study entry immediately before, immediately after, 3.5 h, and 5.5 h after a 30-min walking activity. Cartilage thickness changes in the medial femur and medial tibia were determined from MR images taken at study entry and at 5-year follow-up. Relationships between changes in cartilage thickness and COMP levels, with post-activity concentrations expressed as a percentage of pre-activity levels, were assessed by the calculation of Pearson correlation coefficients and by multiple linear regression analysis, with adjustments for age, sex, and body mass index (BMI).Changes in COMP levels 3.5 h and 5.5 h post-activity were correlated with changes in cartilage thickness in the medial femur and tibia at the 5-year follow-up. The results were strengthened after analyses were adjusted for age, sex, and BMI. Neither baseline pre-activity COMP levels nor changes in COMP levels immediately post-activity were correlated with cartilage thickness changes.The results of this study support the hypothesis that a change in COMP concentration induced by a mechanical stimulus is associated with cartilage thinning at 5 years. Mechanically-induced changes in mechano-sensitive biomarkers should be further explored in the context of stimulus-response models to improve the ability to assess OA progression.

  View details for DOI 10.1016/j.joca.2012.07.018

  View details for Web of Science ID 000309853400013

• Response to 'Plasma proteins present in osteoarthritic synovial fluid can stimulate cytokine production via Toll-like receptor 4' - authors' reply. Arthritis research & therapy Sohn, D. H., Sokolove, J., Sharpe, O., Erhart, J. C., Chandra, P. E., Lahey, L. J., Lindstrom, T. M., Hwang, I., Boyer, K. A., Andriacchi, T. P., Robinson, W. H. 2012; 14 (5): 406

  View details for DOI 10.1186/ar3892

  View details for PubMedID 22979902

  View details for PubMedCentralID PMC3580503

• Characterization of Thigh and Shank Segment Angular Velocity During Jump Landing Tasks Commonly Used to Evaluate Risk for ACL Injury JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME Dowling, A. V., Favre, J., Andriacchi, T. P. 2012; 134 (9)

  Abstract

  The dynamic movements associated with anterior cruciate ligament (ACL) injury during jump landing suggest that limb segment angular velocity can provide important information for understanding the conditions that lead to an injury. Angular velocity measures could provide a quick and simple method of assessing injury risk without the constraints of a laboratory. The objective of this study was to assess the inter-subject variations and the sensitivity of the thigh and shank segment angular velocity in order to determine if these measures could be used to characterize jump landing mechanisms. Additionally, this study tested the correlation between angular velocity and the knee abduction moment. Thirty-six healthy participants (18 male) performed drop jumps with bilateral and unilateral landing. Thigh and shank angular velocities were measured by a wearable inertial-based system, and external knee moments were measured using a marker-based system. Discrete parameters were extracted from the data and compared between systems. For both jumping tasks, the angular velocity curves were well defined movement patterns with high inter-subject similarity in the sagittal plane and moderate to good similarity in the coronal and transverse planes. The angular velocity parameters were also able to detect differences between the two jumping tasks that were consistent across subjects. Furthermore, the coronal angular velocities were significantly correlated with the knee abduction moment (R of 0.28-0.51), which is a strong indicator of ACL injury risk. This study suggested that the thigh and shank angular velocities, which describe the angular dynamics of the movement, should be considered in future studies about ACL injury mechanisms.

  View details for DOI 10.1115/1.4007178

  View details for Web of Science ID 000308415200008

  View details for PubMedID 22938373

• Sensitivity of gait parameters to the effects of anti-inflammatory and opioid treatments in knee osteoarthritis patients JOURNAL OF ORTHOPAEDIC RESEARCH Boyer, K. A., Angst, M. S., Asay, J., Giori, N. J., Andriacchi, T. P. 2012; 30 (7): 1118-1124

  Abstract

  The study aim was to address the need for objective markers of pain-modifying interventions by testing the hypothesis that selective gait measures of knee joint loading can distinguish differences between non-steroidal anti-inflammatory (NSAID), analgesic treatment (opioid-receptor agonist), and placebo in patients medial knee osteoarthritis (OA). A randomized, single-blind washout, double-blind treatment, double-dummy cross-over trial using three treatment arms placebo, opioid (Oxycodone), and NSAID (Celecoxib) in medial compartment knee OA patients. Six patients with Kellgren-Lawrence radiographic severity grades of 2 or 3 completed six testing sessions (gait and pain assessment) at 2-week intervals. A significant increase was found in the knee total reaction moment and vertical ground reaction force (GRF) for Celecoxib compared to placebo (p=0.005, p=0.003), but not for Oxycodone compared to placebo (p=0.20, p=0.27) treatments. Walking speed was significantly higher for the Celecoxib and Oxycodone compared to placebo treatment (p=0.041 and p=0.031, respectively). Self-reported function (WOMAC scores) was not different among treatments (p>0.05). The changes in total reaction moments and GRFs for only the NSAID suggest that greater increases in joint loading occurs when joint inflammation is treated in addition to pain. The total knee reaction moment, representing the magnitude of the extrinsic moment, appears to be a sensitive marker, more so than self-reported metrics, for evaluating knee OA treatment effects.

  View details for DOI 10.1002/jor.22037

  View details for Web of Science ID 000303810000016

  View details for PubMedID 22179861

• Variations in the three-dimensional location and orientation of the ACL in healthy subjects relative to patients after transtibial ACL reconstruction JOURNAL OF ORTHOPAEDIC RESEARCH Scanlan, S. F., Lai, J., Donahue, J. P., Andriacchi, T. P. 2012; 30 (6): 910-918

  Abstract

  Recent reports have indicated that anatomical placement of the anterior cruciate ligament (ACL) graft is an important factor for restoration of joint function following ACL reconstruction. The objective of this study was to address a need for a better understanding of anatomical variations in ACL position and orientation within the joint. Specifically, variations in the ACL anatomy were assessed by testing for side-to-side ACL footprint location symmetry in a healthy population relative to the operative and contralateral knee in a patient population after traditional transtibial single-bundle ACL reconstruction. MRI and three-dimensional modeling techniques were used to determine the in vivo tibiofemoral ACL footprint centers and the resulting ACL orientations in both knees of 30 healthy subjects and 30 subjects after transtibial ACL reconstruction. While there were substantial inter-subject variations in ACL anatomy, the side-to-side RMS differences in the ACL footprint center were 1.20 and 1.34 mm for the femur and tibia, respectively, for the healthy subjects and no clinically meaningful intra-subject differences were measured. However, there were large intra-subject side-to-side differences after transtibial ACL reconstruction, with ACL grafts placed 5.63 and 7.64 mm from the center of the contralateral femoral and tibial ACL footprint centers, respectively. Grafts were placed more medial, anterior, and superior on the femur and more posterior on the tibia; producing grafts that were more vertical in the sagittal and coronal planes. Given the large variation among subjects, these findings advocate the use of the contralateral ACL morphology for retrospectively evaluating patient-specific anatomic graft placement.

  View details for DOI 10.1002/jor.22011

  View details for PubMedID 22105556

• Kinematic adaptations to a variable stiffness shoe: Mechanisms for reducing joint loading JOURNAL OF BIOMECHANICS Boyer, K. A., Federolf, P., Lin, C., Nigg, B. M., Andriacchi, T. P. 2012; 45 (9): 1619-1624

  Abstract

  A recently described variable-stiffness shoe has been shown to reduce the adduction moment and pain in patients with medial-compartment knee osteoarthritis. The mechanism associated with how this device modifies overall gait patterns to reduce the adduction moment is not well understood. Yet this information is important for applying load modifying intervention for the treatment of knee osteoarthritis. A principal component analysis (PCA) was used to test the hypothesis that there are differences in the frontal plane kinematics that are correlated with differences in the ground reaction forces (GRFs) and center of pressure (COP) for a variable-stiffness compared to a constant-stiffness control shoe. Eleven healthy adults were tested in a constant-stiffness control shoe and a variable-stiffness shoe while walking at self-selected speeds. The PCA was performed on trial vectors consisting of all kinematic, GRF and COP data. The projection of trial vectors onto the linear combination of four PCs showed there were significant differences between shoes. The interpretation of the PCs indicated an increase in the ankle eversion, knee abduction and adduction, decreases in the hip adduction and pelvic obliquity angles and reduced excursion of both the COP and peak medial-lateral GRFs for the variable-stiffness compared to the control shoe. The variable-stiffness shoe produced a unique dynamic change in the frontal plane motion of the ankle, hip and pelvis that contributed to changes in the GRF and COP and thus reduced the adduction moment at a critical instant during gait suggesting a different mechanism that was seen with fixed interventions (e.g. wedges).

  View details for DOI 10.1016/j.jbiomech.2012.04.010

  View details for Web of Science ID 000305493000010

  View details for PubMedID 22541945

• Inertial Sensor-Based Feedback Can Reduce Key Risk Metrics for Anterior Cruciate Ligament Injury During Jump Landings AMERICAN JOURNAL OF SPORTS MEDICINE Dowling, A. V., Favre, J., Andriacchi, T. P. 2012; 40 (5): 1075-1083

  Abstract

  The incidence of anterior cruciate ligament (ACL) injury can be decreased through the use of intervention programs. However, the success of these programs is dependent on access to a skilled trainer who provides feedback; as such, these programs would benefit from a simple device with the capacity to provide high-quality feedback.Feedback based on kinematic measurements from a simple inertial sensor-based system can be used to modify key ACL injury risk metrics (knee flexion angle, trunk lean, knee abduction moment) during jump landing.Controlled laboratory study.Seventeen subjects (7 male) were tested during drop jump tasks. Their movements were measured simultaneously with inertial, optoelectronic, and force platform systems. Feedback provided to the subjects was based only on measurements from the inertial sensor-based system (knee flexion angle, trunk lean, and thigh coronal velocity). The subjects conducted a baseline session (without landing instructions), then a training session (with immediate feedback), and finally an evaluation session (without feedback). The baseline and evaluation sessions were then tested for changes in the key risk metrics.The subjects increased their knee flexion angle (16.2°) and trunk lean (17.4°) after the training. They also altered their thigh coronal angular velocity by 29.4 deg/s and reduced their knee abduction moment by 0.5 %BW·Ht. There was a significant correlation (R (2) = 0.55) between the change in thigh coronal angular velocity and the change in knee abduction moment.Subjects reduced key risk metrics for ACL injury after training with the system, suggesting the potential benefit of instrumented feedback for interventional training.Interventional training for reducing the risk of ACL injury could be improved with a simple device that provides immediate feedback.

  View details for DOI 10.1177/0363546512437529

  View details for Web of Science ID 000303323900017

  View details for PubMedID 22459239

• The role of physical activity in changes in walking mechanics with age GAIT & POSTURE Boyer, K. A., Andriacchi, T. P., Beaupre, G. S. 2012; 36 (1): 149-153

  Abstract

  While age-related declines in walking mechanics have been documented, it remains unclear if changes in walking mechanics with age occur as a natural consequence of aging and to what extent these changes are related to a reduction in fitness and physical activity with aging. The study aim was to determine if the walking mechanics of an older (>50) yet highly active population are different from a younger population (<40). Gait mechanics data for 79 middle-aged (50-64 yrs) and 54 older (65-80 yrs) individuals with ≥ 7500 steps/day, based on a 7 day activity monitoring history, and 33 younger adults (ages 18-40) were collected. The older subjects did not reduce self-selected walking speed relative to the younger subjects. However, the walking speed was maintained by increasing cadence while reducing stride-length for middle-aged and older subjects. Middle-aged and older adults had less ankle dorsi-flexion landing at heel-strike and older adults also had less plantar flexion at toe-off. Small decreases in the ankle dorsi-flexion moments (p=0.019, p=0.008) and increases in the hip extension moments (p=0.004, p=0.005) were found for two normalized walking speeds for the middle-aged and older adults compared to the young adults. These results provide quantitative evidence that increased activity with aging can mitigate declines in walking performance and mechanics with age. The high volume of walking activity in the older subjects did not fully prevent changes in gait mechanics, but may have minimized the magnitude of age-related changes on ambulatory function relative to other reports of older inactive subjects.

  View details for DOI 10.1016/j.gaitpost.2012.02.007

  View details for Web of Science ID 000306449100027

  View details for PubMedID 22445586

• Direct comparison of measured and calculated total knee replacement force envelopes during walking in the presence of normal and abnormal gait patterns JOURNAL OF BIOMECHANICS Lundberg, H. J., Foucher, K. C., Andriacchi, T. P., Wimmer, M. A. 2012; 45 (6): 990-996

  Abstract

  Knee joint forces measured from instrumented implants provide important information for testing the validity of computational models that predict knee joint forces. The purpose of this study was to validate a parametric numerical model for predicting knee joint contact forces against measurements from four subjects with instrumented TKRs during the stance phase of gait. Model sensitivity to abnormal gait patterns was also investigated. The results demonstrated good agreement for three subjects with relatively normal gait patterns, where the difference between the mean measured and calculated forces ranged from 0.05 to 0.45 body weights, and the envelopes of measured and calculated forces (from three walking trials) overlapped. The fourth subject, who had a "quadriceps avoidance" external moment pattern, initially had little overlap between the measured and calculated force envelopes. When additional constraints were added, tailored to the subject's gait pattern, the model predictions improved to complete force envelope overlap. Coefficient of multiple determination analysis indicated that the shape of the measured and calculated force waveforms were similar for all subjects (adjusted coefficient of multiple correlation values between 0.88 and 0.92). The parametric model was accurate in predicting both the magnitude and waveform of the contact force, and the accuracy of model predictions was affected by deviations from normal gait patterns. Equally important, the envelope of forces generated by the range of solutions substantially overlapped with the corresponding measured envelope from multiple gait trials for a given subject, suggesting that the variable strategic processes of in vivo force generation are covered by the solution range of this parametric model.

  View details for DOI 10.1016/j.jbiomech.2012.01.015

  View details for Web of Science ID 000302980600013

  View details for PubMedID 22284431

• Effect of variable-stiffness walking shoes on knee adduction moment, pain, and function in subjects with medial compartment knee osteoarthritis after 1 year JOURNAL OF ORTHOPAEDIC RESEARCH Erhart-Hledik, J. C., Elspas, B., Giori, N. J., Andriacchi, T. P. 2012; 30 (4): 514-521

  Abstract

  This study investigated the load-modifying and clinical efficacy of variable-stiffness shoes after 12 months in subjects with medial compartment knee osteoarthritis. Subjects who completed a prior 6-month study were asked to wear their assigned constant-stiffness control or variable-stiffness intervention shoes during the remainder of the study. Changes in peak knee adduction moment, total Western Ontario and McMaster Universities (WOMAC), and WOMAC pain scores were assessed. Seventy-nine subjects were enrolled, and 55 completed the trial. Using an intention-to-treat analysis, the variable-stiffness shoes reduced the within-day peak knee adduction moment (-5.5%, p < 0.001) in the intervention subjects, while the constant-stiffness shoes increased the peak knee adduction moment in the control subjects (+3.1%, p = 0.015) at the 12-month visit. WOMAC pain and total scores for the intervention group were significantly reduced from baseline to 12 months (-32%, p = 0.002 and -35%, p = 0.007, respectively). The control group had a reduction of 27% in WOMAC pain score (p = 0.04) and no significant reduction in total WOMAC score. Reductions in WOMAC pain and total scores were similar between groups (p = 0.8 and p = 0.47, respectively). In the intervention group, reductions in adduction moment were related to improvements in pain and function (R(2)  = 0.11, p = 0.04). Analysis by disease severity revealed greater efficacy in adduction moment reduction in the less severe intervention group. While the long-term effects of the intervention shoes on pain and function did not differ from control, the data suggest wearing the intervention shoe reduces the within-day adduction moment after long-term wear, and thus should reduce loading on the affected medial compartment of the knee.

  View details for DOI 10.1002/jor.21563

  View details for Web of Science ID 000299935900002

  View details for PubMedID 21953877

• Computational modeling of bone density profiles in response to gait: a subject-specific approach BIOMECHANICS AND MODELING IN MECHANOBIOLOGY Pang, H., Shiwalkar, A. P., Madormo, C. M., Taylor, R. E., Andriacchi, T. P., Kuhl, E. 2012; 11 (3-4): 379-390

  Abstract

  The goal of this study is to explore the potential of computational growth models to predict bone density profiles in the proximal tibia in response to gait-induced loading. From a modeling point of view, we design a finite element-based computational algorithm using the theory of open system thermodynamics. In this algorithm, the biological problem, the balance of mass, is solved locally on the integration point level, while the mechanical problem, the balance of linear momentum, is solved globally on the node point level. Specifically, the local bone mineral density is treated as an internal variable, which is allowed to change in response to mechanical loading. From an experimental point of view, we perform a subject-specific gait analysis to identify the relevant forces during walking using an inverse dynamics approach. These forces are directly applied as loads in the finite element simulation. To validate the model, we take a Dual-Energy X-ray Absorptiometry scan of the subject's right knee from which we create a geometric model of the proximal tibia. For qualitative validation, we compare the computationally predicted density profiles to the bone mineral density extracted from this scan. For quantitative validation, we adopt the region of interest method and determine the density values at fourteen discrete locations using standard and custom-designed image analysis tools. Qualitatively, our two- and three-dimensional density predictions are in excellent agreement with the experimental measurements. Quantitatively, errors are less than 3% for the two-dimensional analysis and less than 10% for the three-dimensional analysis. The proposed approach has the potential to ultimately improve the long-term success of possible treatment options for chronic diseases such as osteoarthritis on a patient-specific basis by accurately addressing the complex interactions between ambulatory loads and tissue changes.

  View details for DOI 10.1007/s10237-011-0318-y

  View details for Web of Science ID 000300518000008

  View details for PubMedID 21604146

• A neural network model to predict knee adduction moment during walking based on ground reaction force and anthropometric measurements JOURNAL OF BIOMECHANICS Favre, J., Hayoz, M., Erhart-Hledik, J. C., Andriacchi, T. P. 2012; 45 (4): 692-698

  Abstract

  The external knee adduction moment (KAM) is a major variable for the evaluation of knee loading during walking, specifically in patients with knee osteoarthritis. However, assessment of the KAM is limited to locations where full motion laboratories are available. The purpose of this study was to develop and test a simple method to predict the KAM using only force plate and anthropometric measurements. Three groups of 28 knees (asymptomatic, mild osteoarthritis, and severe osteoarthritis) were studied. Walking trials were collected at different speeds using a motion capture system and a force plate. The reference KAM was calculated by inverse dynamics. For the prediction, inter-subject artificial neural networks were designed using 11 inputs coming from the ground reaction force and the mechanical axis alignment. The predicted KAM curves were similar to the reference curves with median mean absolute deviation (MAD) of 0.36%BW*Ht and median correlation coefficient of 0.966 over 756 individual trials. When comparing mean group curves, the median MAD was 0.09%BW*Ht and the median correlation coefficient 0.998. The peak values and the angular impulses extracted from the predicted and reference curves were significantly correlated, and the same significant differences were obtained among the three groups when the predicted or when the reference curves were used for 95% of the comparisons. In conclusion, this study demonstrated that a simple method using a generic artificial neural network can predict the KAM curve during walking with a high level of significance and provides a practical option for a broader evaluation of the KAM.

  View details for DOI 10.1016/j.jbiomech.2011.11.057

  View details for Web of Science ID 000301748800011

  View details for PubMedID 22257888

• Amplitude and phasing of trunk motion is critical for the efficacy of gait training aimed at reducing ambulatory loads at the knee. Journal of biomechanical engineering Mündermann, A., Mündermann, L., Andriacchi, T. P. 2012; 134 (1): 011010-?

  Abstract

  The purpose of this study was to determine the contribution of changes in amplitude and phasing of medio-lateral trunk sway to a change in the knee adduction moment when walking with increased medio-lateral trunk sway. Kinematic and kinetic data of walking trials with normal and with increased trunk sway were collected for 19 healthy volunteers using a standard motion analysis system. The relationship between the change in first peak knee adduction moment (ΔKAM) and change in trunk sway amplitude (ΔSA; difference between maximum contralateral trunk lean and maximum ipsilateral trunk lean) and phasing (SP; time of heel-strike relative to time of maximum contralateral and time of maximum ipsilateral trunk lean) was determined using nonlinear regression analysis. On average, subjects increased their SA by 9.7 ± 3.6 deg (P < 0.001) with an average SP of 98.8 ± 88.8 ms resulting in an average reduction in the first peak knee adduction moment of -55.2 ± 30.3% (P < 0.001). 64.3% of variability in change in peak knee adduction moment with the increased trunk sway condition was explained by both differences in SA and SP, and the relationship among these parameters was described by the regression equation ΔKAM = 27.220-4.128 [middle dot] ΔSA-64.785 [middle dot] cos(SP). Hence, not only the amplitude but also the phasing of trunk motion is critical. Not only lower limb movement but also lumbar and thoracic lateral flexion should be considered in the decision making process for an optimal intervention aimed at reducing the load on the medial compartment of the knee during walking. However, these promising findings originated from studies on healthy subjects and their relevance for gait training interventions in patients with presumably painful knee osteoarthritis remains to be determined.

  View details for DOI 10.1115/1.4005540

  View details for PubMedID 22482665

• AGING RELATED CHANGES IN THE KINEMATICS OF WALKING: A POTENTIAL PATHWAY TO CHANGES IN CARTILAGE MORPHOLOGY ASME Summer Bioengineering Conference (SBC) Boyer, K. A., Andriacchi, T. P. AMER SOC MECHANICAL ENGINEERS. 2012: 1069–1070

  View details for Web of Science ID 000325036600534

• VALGUS KNEE ALIGNMENT, NOT STEP WIDTH OR TOE-OUT CAUSE REDUCED KNEE ADDUCTION MOMENT IN THE HEALTHY OBESE ASME Summer Bioengineering Conference (SBC) Blazek, K., Asay, J., Erhart-Hledik, J., Andriacchi, T. AMER SOC MECHANICAL ENGINEERS. 2012: 235–236

  View details for Web of Science ID 000325036600117

• Amplitude and Phasing of Trunk Motion is Critical for the Efficacy of Gait Training Aimed at Reducing Ambulatory Loads at the Knee JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME Muendermann, A., Muendermann, L., Andriacchi, T. P. 2012; 134 (1)

  View details for DOI 10.1115/1.4005540

  View details for Web of Science ID 000302582100010

• EFFECT OF PARTIAL MEDIAL MENISCECTOMY ON THE INTERACTION BETWEEN PRIMARY AND SECONDARY KNEE MOTION DURING GAIT ASME Summer Bioengineering Conference (SBC) Edd, S. N., Netravali, N. A., Giori, N. J., Andriacchi, T. P. AMER SOC MECHANICAL ENGINEERS. 2012: 1061–1062

  View details for Web of Science ID 000325036600530

• Plasma proteins present in osteoarthritic synovial fluid can stimulate cytokine production via Toll-like receptor 4 ARTHRITIS RESEARCH & THERAPY Sohn, D. H., Sokolove, J., Sharpe, O., Erhart, J. C., Chandra, P. E., Lahey, L. J., Lindstrom, T. M., Hwang, I., Boyer, K. A., Andriacchi, T. P., Robinson, W. H. 2012; 14 (1)

  Abstract

  Osteoarthritis (OA) is a degenerative disease characterized by cartilage breakdown in the synovial joints. The presence of low-grade inflammation in OA joints is receiving increasing attention, with synovitis shown to be present even in the early stages of the disease. How the synovial inflammation arises is unclear, but proteins in the synovial fluid of affected joints could conceivably contribute. We therefore surveyed the proteins present in OA synovial fluid and assessed their immunostimulatory properties.We used mass spectrometry to survey the proteins present in the synovial fluid of patients with knee OA. We used a multiplex bead-based immunoassay to measure levels of inflammatory cytokines in serum and synovial fluid from patients with knee OA and from patients with rheumatoid arthritis (RA), as well as in sera from healthy individuals. Significant differences in cytokine levels between groups were determined by significance analysis of microarrays, and relations were determined by unsupervised hierarchic clustering. To assess the immunostimulatory properties of a subset of the identified proteins, we tested the proteins' ability to induce the production of inflammatory cytokines by macrophages. For proteins found to be stimulatory, the macrophage stimulation assays were repeated by using Toll-like receptor 4 (TLR4)-deficient macrophages.We identified 108 proteins in OA synovial fluid, including plasma proteins, serine protease inhibitors, proteins indicative of cartilage turnover, and proteins involved in inflammation and immunity. Multiplex cytokine analysis revealed that levels of several inflammatory cytokines were significantly higher in OA sera than in normal sera, and levels of inflammatory cytokines in synovial fluid and serum were, as expected, higher in RA samples than in OA samples. As much as 36% of the proteins identified in OA synovial fluid were plasma proteins. Testing a subset of these plasma proteins in macrophage stimulation assays, we found that Gc-globulin, α1-microglobulin, and α2-macroglobulin can signal via TLR4 to induce macrophage production of inflammatory cytokines implicated in OA.Our findings suggest that plasma proteins present in OA synovial fluid, whether through exudation from plasma or production by synovial tissues, could contribute to low-grade inflammation in OA by functioning as so-called damage-associated molecular patterns in the synovial joint.

  View details for DOI 10.1186/ar3555

  View details for Web of Science ID 000304698800021

  View details for PubMedID 22225630

  View details for PubMedCentralID PMC3392793

• Kinematics Differences Between the Flat, Kick, and Slice Serves Measured Using a Markerless Motion Capture Method ANNALS OF BIOMEDICAL ENGINEERING Sheets, A. L., Abrams, G. D., Corazza, S., Safran, M. R., Andriacchi, T. P. 2011; 39 (12): 3011-3020

  Abstract

  Tennis injuries have been associated with serving mechanics, but quantitative kinematic measurements in realistic environments are limited by current motion capture technologies. This study tested for kinematic differences at the lower back, shoulder, elbow, wrist, and racquet between the flat, kick, and slice serves using a markerless motion capture (MMC) system. Seven male NCAA Division 1 players were tested on an outdoor court in daylight conditions. Peak racquet and joint center speeds occurred sequentially and increased from proximal (back) to distal (racquet). Racquet speeds at ball impact were not significantly different between serve types. However, there were significant differences in the direction of the racquet velocity vector between serves: the kick serve had the largest lateral and smallest forward racquet velocity components, while the flat serve had the smallest vertical component (p < 0.01). The slice serve had lateral velocity, like the kick, and large forward velocity, like the flat. Additionally, the racquet in the kick serve was positioned 8.7 cm more posterior and 21.1 cm more medial than the shoulder compared with the flat, which could suggest an increased risk of shoulder and back injury associated with the kick serve. This study demonstrated the potential for MMC for testing sports performance under natural conditions.

  View details for DOI 10.1007/s10439-011-0418-y

  View details for Web of Science ID 000296507000014

  View details for PubMedID 21984513

• Maintaining femoral bone density in adults: how many steps per day are enough? OSTEOPOROSIS INTERNATIONAL Boyer, K. A., Kiratli, B. J., Andriacchi, T. P., Beaupre, G. S. 2011; 22 (12): 2981-2988

  Abstract

  The amount and intensity of walking to maintain a healthy skeleton is unknown. This study examined the relationship between habitual walking activity and femoral bone mineral density (BMD) in healthy individuals using a quantitative theory for bone maintenance. Our results suggest a gender, weight, and speed sensitivity of walking interventions.Walking has been extensively promoted for the prevention of osteoporosis. The amount and intensity of walking to maintain a healthy skeleton is unknown and evidence to support a specific target of steps per day is lacking. The goal of our study was to examine the relationship between habitual walking activity and femoral bone mineral density (BMD) in healthy individuals using a quantitative theory for bone maintenance.Habitual walking activity and total femur BMD were measured in 105 individuals (49-64 years). An index of cumulative loading (bone density index, BDI) was examined as a predictor of BMD. The BDI-BMD relationship was used to predict the steps per day to maintain healthy BMD values for a range of body weights (BW) and walking speeds.For females but not for males, BDI was correlated with BMD (r (2) = 0.19, p < 0.001). The total required steps per day to maintain a T-score of -1.0 for a female with the average BW of the study cohort, walking at 1.00 m/s is 4,892 steps/day. Substantially more steps (18,568 steps/day) are required for a female with a BW 20% lighter than the average for our female cohort. For these lighter females, only at a walking speed greater than 1.32 m/s was 10,000 steps/day sufficient to maintain a T-score of -1.0.Our results suggest a gender, weight, and speed sensitivity of walking interventions for osteoporosis. In persons of low BW, the necessary steps per day to maintain BMD can be substantially greater than the often-quoted 10,000 steps.

  View details for DOI 10.1007/s00198-011-1538-9

  View details for Web of Science ID 000297151200006

  View details for PubMedID 21318440

• Valgus Plus Internal Rotation Moments Increase Anterior Cruciate Ligament Strain More Than Either Alone MEDICINE AND SCIENCE IN SPORTS AND EXERCISE Shin, C. S., Chaudhari, A. M., Andriacchi, T. P. 2011; 43 (8): 1484-1491

  Abstract

  To test the influence of combined knee valgus and internal tibial rotation moment on anterior cruciate ligament (ACL) strain during single-leg landing. We tested the following hypotheses: the combination of the valgus and internal rotation moments observed during single-leg landing produces a higher ACL strain than either moment applied individually, the combined rotational moments at the physiological levels observed could theoretically increase strain in the ACL high enough to rupture the ACL, and the location of the peak contact force was at the posterior-lateral side for combined loading.The study was conducted by applying in vivo human loading data to a validated simulation model of the three-dimensional dynamic knee joint to predict ACL strains.The peak ACL strain increased nonlinearly when either applied valgus moment or internal rotation moment was increased in the model. When the two rotational moments were applied individually, neither caused ACL strain >0.077. However, when applied in combination, the two rotational moments had a much larger effect, and the predicted peak ACL strain increased up to 0.105. During landing, the peak contact force occurred at the posterior-lateral side of the tibial cartilage in the model when the combined maximum valgus moment and tibial internal rotation moments were applied.Combined knee valgus and internal rotation moments increases ACL strain more than either alone. The combination of a valgus and internal rotational moment at magnitudes that occurs in vivo during landing can cause ACL strains that may be high enough to cause ACL rupture. This predicted high ACL strain and the contact force location suggest that combined valgus and internal tibial rotational moments during single-leg landing are relevant to ACL injuries.

  View details for DOI 10.1249/MSS.0b013e31820f8395

  View details for Web of Science ID 000292773000013

  View details for PubMedID 21266934

• Preoperative and Postoperative Sagittal Plane Hip Kinematics in Patients With Femoroacetabular Impingement During Level Walking AMERICAN JOURNAL OF SPORTS MEDICINE Rylander, J. H., Shu, B., Andriacchi, T. P., Safran, M. R. 2011; 39: 36S-42S

  Abstract

  Femoroacetabular impingement (FAI) has been linked to osteoarthritis. Treatment options range from nonoperative to operative, and current outcome measures are generally subjective or not conducted under actual activities of daily living. Thus, there is a need for the use of motion capture techniques to quantitatively assess the outcome of surgical intervention for those treated for FAI.The gait of FAI patients 1 year after operative treatment (arthroscopic hip reshaping) will be significantly closer to the normal range and pattern of hip flexion motion, relative to pretreatment.Case series; Level of evidence, 4.Eleven patients between 18 and 44 years of age with diagnosed FAI were enrolled in this study. Kinematics and kinetics for this group of patients were collected using motion capture techniques before arthroscopic bone-reshaping surgery and again 1 year after surgery. Pain and perceived activity level (Tegner scale) were also collected. All collected data were compared using a paired t test.Overall hip sagittal plane range of motion increased on the affected side from 27.6° ± 5.0° to 30.7° ± 4.3° (P = .02). The presence of abnormal reversals (second-order change in the slope in the hip flexion/extension curve) that was present in 5 patients preoperatively disappeared or was reduced in prevalence and magnitude in 4 of the patients postoperatively. Additionally, pain decreased and activity level increased postoperatively.The results supported the hypothesis that surgical intervention for FAI restores more normal patterns of gait and provides objective support that the surgical procedure is useful. The results help establish motion capture as a potential method for quantitatively assessing the outcome in FAI surgical interventions. The presence of abnormal reversals in hip flexion has been reported in end-stage hip osteoarthritis, and the presence of these reversals in FAI patients reinforces the idea of FAI being a precursor to hip osteoarthritis.

  View details for DOI 10.1177/0363546511413993

  View details for Web of Science ID 000292167400006

  View details for PubMedID 21709030

• A Wearable System to Assess Risk for Anterior Cruciate Ligament Injury During Jump Landing: Measurements of Temporal Events, Jump Height, and Sagittal Plane Kinematics JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME Dowling, A. V., Favre, J., Andriacchi, T. P. 2011; 133 (7)

  Abstract

  The incidence of anterior cruciate ligament (ACL) injury remains high, and there is a need for simple, cost effective methods to identify athletes at a higher risk for ACL injury. Wearable measurement systems offer potential methods to assess the risk of ACL injury during jumping tasks. The objective of this study was to assess the capacity of a wearable inertial-based system to evaluate ACL injury risk during jumping tasks. The system accuracy for measuring temporal events (initial contact, toe-off), jump height, and sagittal plane angles (knee, trunk) was assessed by comparing results obtained with the wearable system to simultaneous measurements obtained with a marker-based optoelectronic reference system. Thirty-eight healthy participants (20 male and 18 female) performed drop jumps with bilateral and unilateral support landing. The mean differences between the temporal events obtained with both systems were below 5 ms, and the precisions were below 24 ms. The mean jump heights measured with both systems differed by less than 1 mm, and the associations (Pearson correlation coefficients) were above 0.9. For the discrete angle parameters, there was an average association of 0.91 and precision of 3.5° for the knee flexion angle and an association of 0.77 and precision of 5.5° for the trunk lean. The results based on the receiver-operating characteristic (ROC) also demonstrated that the proposed wearable system could identify movements at higher risk for ACL injury. The area under the ROC plots was between 0.89 and 0.99 for the knee flexion angle and between 0.83 and 0.95 for the trunk lean. The wearable system demonstrated good concurrent validity with marker-based measurements and good discriminative performance in terms of the known risk factors for ACL injury. This study suggests that a wearable system could be a simple cost-effective tool for conducting risk screening or for providing focused feedback.

  View details for DOI 10.1115/1.4004413

  View details for Web of Science ID 000293524800008

  View details for PubMedID 21823747

• Knee joint kinematics during walking influences the spatial cartilage thickness distribution in the knee JOURNAL OF BIOMECHANICS Koo, S., Rylander, J. H., Andriacchi, T. P. 2011; 44 (7): 1405-1409

  Abstract

  The regional adaptation of knee cartilage morphology to the kinematics of walking has been suggested as an important factor in the evaluation of the consequences of alteration in normal gait leading to osteoarthritis. The purpose of this study was to investigate the association of spatial cartilage thickness distributions of the femur and tibia in the knee to the knee kinematics during walking. Gait data and knee MR images were obtained from 17 healthy volunteers (age 33.2 ± 9.8 years). Cartilage thickness maps were created for the femoral and tibial cartilage. Locations of thickest cartilage in the medial and lateral compartments in the femur and tibia were identified using a numerical method. The flexion-extension (FE) angle associated with the cartilage contact regions on the femur, and the anterior-posterior (AP) translation and internal-external (IE) rotation associated with the cartilage contact regions on the tibia at the heel strike of walking were tested for correlation with the locations of thickest cartilage. The locations of the thickest cartilage had relatively large variation (SD, 8.9°) and was significantly associated with the FE angle at heel strike only in the medial femoral condyle (R(2)=0.41, p<0.01). The natural knee kinematics and contact surface shapes seem to affect the functional adaptation of knee articular cartilage morphology. The sensitivity of cartilage morphology to kinematics at the knee during walking suggests that regional cartilage thickness variations are influenced by both loading and the number of loading cycles. Thus walking is an important consideration in the analysis of the morphological variations of articular cartilage, since it is the dominant cyclic activity of daily living. The sensitivity of cartilage morphology to gait kinematics is also important in understanding the etiology and pathomechanics of osteoarthritis.

  View details for DOI 10.1016/j.jbiomech.2010.11.020

  View details for Web of Science ID 000291075800027

  View details for PubMedID 21371712

• An analysis of the mechanisms for reducing the knee adduction moment during walking using a variable stiffness shoe in subjects with knee osteoarthritis JOURNAL OF BIOMECHANICS Jenkyn, T. R., Erhart, J. C., Andriacchi, T. P. 2011; 44 (7): 1271-1276

  Abstract

  Variable stiffness shoes that have a stiffer lateral than medial sole may reduce the external knee adduction moment (EKAM) and pain during walking in patients with medial compartment knee osteoarthritis (OA). However, the mechanism by which EKAM may be reduced in the OA knee with this intervention remains unclear. Three hypotheses were tested in this study: (1) The reduction in EKAM during walking with the variable stiffness shoe is associated with a reduction in GRF magnitude and/or (2) frontal plane lever arm. (3) A reduction in frontal plane lever arm occurs either by moving the center of pressure laterally under the shoe and/or by dynamically reducing the medial component of GRF. Thirty-two subjects (20 male, 12 female; age: 58.7 ± 9.3 years; height: 1.62 ± 0.08 m; mass: 81.3 ± 14.6 kg) with medial compartment knee osteoarthritis were studied walking in a gait laboratory. The frontal plane lever arm was significantly reduced (1.62%, 0.07%ht, p=0.02) on the affected side while the magnitude of the GRF was not significantly changed. The reduction in the lever arm was weakly correlated with a medial shift in the COP. However, the combined medial shift in the COP and reduction in the medial GRF explained 50% of the change of the frontal plane lever arm. These results suggest that the medial shift in the COP at the foot produced by the intervention shoe stimulates an adaptive dynamic response during gait that reduces the frontal plane lever arm.

  View details for DOI 10.1016/j.jbiomech.2011.02.013

  View details for Web of Science ID 000291075800007

  View details for PubMedID 21396645

• The Effect of Kinematic and Kinetic Changes on Meniscal Strains During Gait JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME Netravali, N. A., Koo, S., Giori, N. J., Andriacchi, T. P. 2011; 133 (1)

  Abstract

  The menisci play an important role in load distribution, load bearing, joint stability, lubrication, and proprioception. Partial meniscectomy has been shown to result in changes in the kinematics and kinetics at the knee during gait that can lead to progressive meniscal degeneration. This study examined changes in the strains within the menisci associated with kinematic and kinetic changes during the gait cycle. The gait changes considered were a 5 deg shift toward external rotation of the tibia with respect to the femur and an increased medial-lateral load ratio representing an increased adduction moment. A finite element model of the knee was developed and tested using a cadaveric specimen. The cadaver was placed in positions representing heel-strike and midstance of the normal gait, and magnetic resonance images were taken. Comparisons of the model predictions to boundaries digitized from images acquired in the loaded states were within the errors produced by a 1 pixel shift of either meniscus. The finite element model predicted that an increased adduction moment caused increased strains of both the anterior and posterior horns of the medial meniscus. The lateral meniscus exhibited much lower strains and had minimal changes under the various loading conditions. The external tibial rotational change resulted in a 20% decrease in the strains in the posterior medial horn and increased strains in the anterior medial horn. The results of this study suggest that the shift toward external tibial rotation seen clinically after partial medial meniscectomy is not likely to cause subsequent degenerative medial meniscal damage, but the consequence of this kinematic shift on the pathogenesis of osteoarthritis following meniscectomy requires further consideration.

  View details for DOI 10.1115/1.4003008

  View details for Web of Science ID 000285767600006

  View details for PubMedID 21186896

• Review of tennis serve motion analysis and the biomechanics of three serve types with implications for injury SPORTS BIOMECHANICS Abrams, G. D., Sheets, A. L., Andriacchi, T. P., Safran, M. R. 2011; 10 (4): 378-390

  Abstract

  The tennis serve has the potential for musculoskeletal injury as it is an overhead motion and is performed repetitively during play. Early studies evaluating the biomechanics and injury potential of the tennis serve utilized skin-based marker technologies; however, markerless motion measurement systems have recently become available and have obviated some of the problems associated with the marker-based technology. The late cocking and early acceleration phases of the kinetic chain of the service motion produce the highest internal forces and pose the greatest risk of injury during the service motion. Previous biomechanical data on the tennis serve have primarily focused on the flat serve, with some data on the kick serve, and very little published data elucidating the biomechanics of the slice serve. This review discusses the injury potential of the tennis serve with respect to the four phases of the service motion, the history, and early findings of service motion evaluation, as well as biomechanical data detailing the differences between the three types of serves and how this may relate to injury prevention, rehabilitation, and return to play.

  View details for DOI 10.1080/14763141.2011.629302

  View details for Web of Science ID 000299832400010

  View details for PubMedID 22303788

• Changes in In Vivo Knee Loading with a Variable-Stiffness Intervention Shoe Correlate with Changes in the Knee Adduction Moment JOURNAL OF ORTHOPAEDIC RESEARCH Erhart, J. C., Dyrby, C. O., D'Lima, D. D., Colwell, C. W., Andriacchi, T. P. 2010; 28 (12): 1548-1553

  Abstract

  External knee adduction moment can be reduced using footwear interventions, but the exact changes in in vivo medial joint loading remain unknown. An instrumented knee replacement was used to assess changes in in vivo medial joint loading in a single patient walking with a variable-stiffness intervention shoe. We hypothesized that during walking with a load modifying variable-stiffness shoe intervention: (1) the first peak knee adduction moment will be reduced compared to a subject's personal shoes; (2) the first peak in vivo medial contact force will be reduced compared to personal shoes; and (3) the reduction in knee adduction moment will be correlated with the reduction in medial contact force. The instrumentation included a motion capture system, force plate, and the instrumented knee prosthesis. The intervention shoe reduced the first peak knee adduction moment (13.3%, p = 0.011) and medial compartment joint contact force (12.3%; p = 0.008) compared to the personal shoe. The change in first peak knee adduction moment was significantly correlated with the change in first peak medial contact force (R(2) = 0.67, p = 0.007). Thus, for a single subject with a total knee prosthesis the variable-stiffness shoe reduces loading on the affected compartment of the joint. The reductions in the external knee adduction moment are indicative of reductions in in vivo medial compressive force with this intervention.

  View details for DOI 10.1002/jor.21183

  View details for Web of Science ID 000284026000002

  View details for PubMedID 20973058

  View details for PubMedCentralID PMC2965044

• Partial medial meniscectomy and rotational differences at the knee during walking JOURNAL OF BIOMECHANICS Netravali, N. A., Giori, N. J., Andriacchi, T. P. 2010; 43 (15): 2948-2953

  Abstract

  Loss of meniscal function due to injury or partial meniscectomy is common and represents a significant risk factor for premature osteoarthritis. The menisci can influence the transverse plane movements (anterior-posterior (AP) translation and internal-external (IE) rotation) of the knee during walking. While walking is the most frequent activity of daily living, the kinematic differences at the knee during walking associated with the meniscal injury are not well understood. This study examined the influence of partial medial meniscectomy (PMM) on the kinematics and kinetics of the knee during the stance phase of gait by testing the differences in anterior-posterior translation, internal-external rotation, knee flexion range of movement, peak flexion/extension moments, and adduction moments between the PMM and healthy contralateral limbs. Ten patients (45±9 years old, height 1.75±0.06m, weight 76.7±13.5kg) who had undergone partial medial meniscectomy (33±100 months post-op) in one limb with a healthy contralateral limb were tested during normal walking. The contralateral limb was compared to a matched control group and no differences were found. The primary kinematic difference was a significantly greater external rotation (3.2°) of the tibia that existed through stance phase, with 8 of 10 subjects demonstrating the same pattern. The PMM subjects also exhibited significantly lower peak flexion and extension moments in their PMM limbs. The altered rotational position found likely results in changes of tibio-femoral contact during walking and could cause the type of degenerative changes found in the articular cartilage following meniscal injury.

  View details for DOI 10.1016/j.jbiomech.2010.07.013

  View details for Web of Science ID 000285122900013

  View details for PubMedID 20719317

• Changes in knee adduction moment, pain, and functionality with a variable-stiffness walking shoe after 6 months. Journal of orthopaedic research Erhart, J. C., Mündermann, A., Elspas, B., Giori, N. J., Andriacchi, T. P. 2010; 28 (7): 873-879

  Abstract

  This study tested the effects of variable-stiffness shoes on knee adduction moment, pain, and function in subjects with symptoms of medial compartment knee osteoarthritis over 6 months. Patients were randomly and blindly assigned to a variable-stiffness intervention or constant-stiffness control shoe. The Western Ontario and McMaster Universities (WOMAC) score served as the primary outcome measure. Joint loading, the secondary outcome measure, was assessed using the external knee adduction moment. Peak external knee adduction moment, total WOMAC, and WOMAC pain scores were assessed at baseline and after 6 months. The total WOMAC and WOMAC pain scores for the intervention group were reduced from baseline to 6 months (p = 0.017 and p = 0.002, respectively), with no significant reductions for the control group. There was no difference between groups in magnitude of the reduction in total WOMAC (p = 0.50) or WOMAC pain scores (p = 0.31). The proportion of patients achieving a clinically important improvement in pain was greater in the intervention group than in the control group (p = 0.012). The variable-stiffness shoes reduced the peak knee adduction moment (-6.6% vs. control, p < 0.001) in the 34 intervention subjects at 6 months. The adduction moment reduction significantly improved (p = 0.03) from the baseline reduction. The constant-stiffness control shoe increased the peak knee adduction moment (+6.3% vs. personal, p = 0.004) in the 26 control subjects at 6 months. The results of this study showed that wearing the variable-stiffness shoe lowered the adduction moment, reduced pain, and improved functionality after 6 months of wear. The lower adduction moment associated with wearing this shoe may slow the rate of progression of osteoarthritis after long-term use.

  View details for DOI 10.1002/jor.21077

  View details for PubMedID 20058261

• Changes in Knee Adduction Moment, Pain, and Functionality with a Variable-Stiffness Walking Shoe after 6 Months JOURNAL OF ORTHOPAEDIC RESEARCH Erhart, J. C., Muendermann, A., Elspas, B., Giori, N. J., Andriacchi, T. P. 2010; 28 (7): 873-879

  Abstract

  This study tested the effects of variable-stiffness shoes on knee adduction moment, pain, and function in subjects with symptoms of medial compartment knee osteoarthritis over 6 months. Patients were randomly and blindly assigned to a variable-stiffness intervention or constant-stiffness control shoe. The Western Ontario and McMaster Universities (WOMAC) score served as the primary outcome measure. Joint loading, the secondary outcome measure, was assessed using the external knee adduction moment. Peak external knee adduction moment, total WOMAC, and WOMAC pain scores were assessed at baseline and after 6 months. The total WOMAC and WOMAC pain scores for the intervention group were reduced from baseline to 6 months (p = 0.017 and p = 0.002, respectively), with no significant reductions for the control group. There was no difference between groups in magnitude of the reduction in total WOMAC (p = 0.50) or WOMAC pain scores (p = 0.31). The proportion of patients achieving a clinically important improvement in pain was greater in the intervention group than in the control group (p = 0.012). The variable-stiffness shoes reduced the peak knee adduction moment (-6.6% vs. control, p < 0.001) in the 34 intervention subjects at 6 months. The adduction moment reduction significantly improved (p = 0.03) from the baseline reduction. The constant-stiffness control shoe increased the peak knee adduction moment (+6.3% vs. personal, p = 0.004) in the 26 control subjects at 6 months. The results of this study showed that wearing the variable-stiffness shoe lowered the adduction moment, reduced pain, and improved functionality after 6 months of wear. The lower adduction moment associated with wearing this shoe may slow the rate of progression of osteoarthritis after long-term use.

  View details for DOI 10.1002/jor.21077

  View details for Web of Science ID 000278654500006

• Gait Modification via Verbal Instruction and an Active Feedback System to Reduce Peak Knee Adduction Moment JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME Dowling, A. V., Fisher, D. S., Andriacchi, T. P. 2010; 132 (7)

  Abstract

  The purpose of this study was to introduce a simple gait training method using real-time gait modification to reduce the peak knee adduction moment during walking by producing a subtle weight bearing shift to the medial side of the foot. The hypothesis of this study was that this weight shift could be achieved via either verbal instruction or an active feedback system, and that the weight shift would result in a reduction in the first peak knee adduction moment compared with the control tests. Nine individuals were tested during walking using two intervention methods: verbal instruction and an active feedback system placed on the right shoe. The first peak of the knee adduction moment for each condition was assessed using a motion capture system and force plate. The active feedback system significantly reduced (14.2%) the peak knee adduction moment relative to the control. This study demonstrated that a subtle weight bearing shift to the medial side of the foot produced with an active feedback system during walking reduced the first peak of the knee adduction moment and suggests the potential application of this method to slow the rate of progression of medial compartment knee osteoarthritis.

  View details for DOI 10.1115/1.4001584

  View details for Web of Science ID 000279631400007

  View details for PubMedID 20590285

• Gait Changes in Patients With Knee Osteoarthritis Are Replicated by Experimental Knee Pain ARTHRITIS CARE & RESEARCH Henriksen, M., Graven-Nielsen, T., Aaboe, J., Andriacchi, T. P., Bliddal, H. 2010; 62 (4): 501-509

  Abstract

  Medial knee osteoarthritis (OA) is characterized by pain and associated with abnormal knee moments during walking. The relationship between knee OA pain and gait changes remains to be clarified, and a better understanding of this link could advance the treatment and prevention of disease progression. This study investigated changes in knee moments during walking following experimental knee pain in healthy volunteers, and whether these changes replicated the joint moments observed in medial knee OA patients.In a crossover study, 34 healthy subjects were tested on 3 different days; gait analyses were conducted before, during, and after pain induced by hypertonic saline injections (0.75 ml) into the infrapatellar fat pad. Isotonic saline and sham injections were used as control conditions. Peak moments in frontal and sagittal planes were analyzed. The results were compared with data from 161 medial knee OA patients. The patients were divided into less severe OA and severe OA categories, which was based on radiographic disease severity of the medial compartment.Experimental knee pain led to reduced peak moments in the frontal and sagittal planes in the healthy subjects, which were similar to the patterns observed in less severe OA patients while walking at the same speed.In healthy subjects, pain was associated with reductions in knee joint moments during walking in a manner similar to less severe knee OA patients. The experimental model may be used to study mechanically-driven knee OA progression and preventive measures against abnormal joint loading in knee OA.

  View details for DOI 10.1002/acr.20033

  View details for Web of Science ID 000280979400011

  View details for PubMedID 20391505

• Automatic Generation of a Subject-Specific Model for Accurate Markerless Motion Capture and Biomechanical Applications IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING Corazza, S., Gambaretto, E., Mundermann, L., Andriacchi, T. P. 2010; 57 (4): 806-812

  Abstract

  A novel approach for the automatic generation of a subject-specific model consisting of morphological and joint location information is described. The aim is to address the need for efficient and accurate model generation for markerless motion capture (MMC) and biomechanical studies. The algorithm applied and expanded on previous work on human shapes space by embedding location information for ten joint centers in a subject-specific free-form surface. The optimal locations of joint centers in the 3-D mesh were learned through linear regression over a set of nine subjects whose joint centers were known. The model was shown to be sufficiently accurate for both kinematic (joint centers) and morphological (shape of the body) information to allow accurate tracking with MMC systems. The automatic model generation algorithm was applied to 3-D meshes of different quality and resolution such as laser scans and visual hulls. The complete method was tested using nine subjects of different gender, body mass index (BMI), age, and ethnicity. Experimental training error and cross-validation errors were 19 and 25 mm, respectively, on average over the joints of the ten subjects analyzed in the study.

  View details for DOI 10.1109/TBME.2008.2002103

  View details for Web of Science ID 000275998200005

  View details for PubMedID 19272951

• Markerless Motion Capture through Visual Hull, Articulated ICP and Subject Specific Model Generation INTERNATIONAL JOURNAL OF COMPUTER VISION Corazza, S., Muendermann, L., Gambaretto, E., Ferrigno, G., Andriacchi, T. P. 2010; 87 (1-2): 156-169

  View details for DOI 10.1007/s11263-009-0284-3

  View details for Web of Science ID 000273242300009

• Shoe-Surface Friction Influences Movement Strategies During a Sidestep Cutting Task Implications for Anterior Cruciate Ligament Injury Risk AMERICAN JOURNAL OF SPORTS MEDICINE Dowling, A. V., Corazza, S., Chaudhari, A. M., Andriacchi, T. P. 2010; 38 (3): 478-485

  Abstract

  Increasing the coefficient of friction of the shoe-surface interaction has been shown to lead to increased incidence of anterior cruciate ligament (ACL) injuries, but the causes for this increase are unknown. Previous studies indicate that specific biomechanical measures during landing are associated with an increased risk for ACL injury.At foot contact during a sidestep cutting task, subjects use different movement strategies for shoe-surface conditions with a high coefficient of friction (COF) relative to a low friction condition. Specifically, the study tested for significant differences in knee kinematics, external knee moments, and the position of the center of mass for different COFs.Controlled laboratory study.Twenty-two healthy subjects (11 male) were evaluated performing a 30 degrees sidestep cutting task on a low friction surface (0.38) and a high friction surface (0.87) at a constant speed. An 8-camera markerless motion capture system combined with 2 force plates was used to measure full-body kinematics, kinetics, and center of mass.At foot contact, subjects had a lower knee flexion angle (P = .01), lower external knee flexion moment (P < .001), higher external knee valgus moment (P < .001), and greater medial distance of the center of mass from the support limb (P < .001) on the high friction surface relative to the low friction surface.The high COF shoe-surface condition was associated with biomechanical conditions that can increase the risk of ACL injury. The higher incidence of ACL injury observed on high friction surfaces could be a result of these biomechanical changes. The differences in the biomechanical variables were the result of an anticipated stimulus due to different surface friction, with other conditions remaining constant.The risk analysis of ACL injury should consider the biomechanical movement changes that occur for a shoe-surface condition with high friction.

  View details for DOI 10.1177/0363546509348374

  View details for Web of Science ID 000274803800006

  View details for PubMedID 20194954

• Muscle and Joint Function in Human Locomotion ANNUAL REVIEW OF BIOMEDICAL ENGINEERING, VOL 12 Pandy, M. G., Andriacchi, T. P. 2010; 12: 401-433

  Abstract

  This review describes how computational modeling can be combined with noninvasive gait measurements to describe and explain muscle and joint function in human locomotion. Five muscles--the gluteus maximus, gluteus medius, vasti, soleus, and gastrocnemius--contribute most significantly to the accelerations of the center of mass in the vertical, fore-aft, and medio-lateral directions when humans walk and run at their preferred speeds. Humans choose to switch from a walk to a run at speeds near 2 m s(-1) to enhance the biomechanical performance of the ankle plantarflexors and to improve coordination of the knee and ankle muscles during stance. Muscles that do not span a joint can contribute to the contact force transmitted by that joint and therefore affect its stability. In walking, for example, uniarticular muscles that cross the hip and ankle act to create the adduction moment at the knee, thereby contributing to the contact force present in the medial compartment.

  View details for DOI 10.1146/annurev-bioeng-070909-105259

  View details for Web of Science ID 000281447400016

  View details for PubMedID 20617942

• REDUCTION IN THE KNEE ADDUCTION MOMENT DURING WALKING USING LATERALLY-WEDGED SHOES WITH AND WITHOUT ANKLE SUPPORT 12th ASME Summer Bioengineering Conference Erhart, J., Andriacchi, T. AMER SOC MECHANICAL ENGINEERS. 2010: 307–308

  View details for Web of Science ID 000290705300154

• RELATIONSHIP OF KNEE ARTICULAR CARTILAGE THICKNESS TO BODY MASS INDEX AND GAIT MECHANICS 12th ASME Summer Bioengineering Conference Blazek, K., Erhart, J., Asay, J., Andriacchi, T. AMER SOC MECHANICAL ENGINEERS. 2010: 411–412

  View details for Web of Science ID 000290705300206

• An Automated Image-Based Method of 3D Subject-Specific Body Segment Parameter Estimation for Kinetic Analyses of Rapid Movements JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME Sheets, A. L., Corazza, S., Andriacchi, T. P. 2010; 132 (1)

  Abstract

  Accurate subject-specific body segment parameters (BSPs) are necessary to perform kinetic analyses of human movements with large accelerations, or no external contact forces or moments. A new automated topographical image-based method of estimating segment mass, center of mass (CM) position, and moments of inertia is presented. Body geometry and volume were measured using a laser scanner, then an automated pose and shape registration algorithm segmented the scanned body surface, and identified joint center (JC) positions. Assuming the constant segment densities of Dempster, thigh and shank masses, CM locations, and moments of inertia were estimated for four male subjects with body mass indexes (BMIs) of 19.7-38.2. The subject-specific BSP were compared with those determined using Dempster and Clauser regression equations. The influence of BSP and BMI differences on knee and hip net forces and moments during a running swing phase were quantified for the subjects with the smallest and largest BMIs. Subject-specific BSP for 15 body segments were quickly calculated using the image-based method, and total subject masses were overestimated by 1.7-2.9%.When compared with the Dempster and Clauser methods, image-based and regression estimated thigh BSP varied more than the shank parameters. Thigh masses and hip JC to thigh CM distances were consistently larger, and each transverse moment of inertia was smaller using the image-based method. Because the shank had larger linear and angular accelerations than the thigh during the running swing phase, shank BSP differences had a larger effect on calculated intersegmental forces and moments at the knee joint than thigh BSP differences did at the hip. It was the net knee kinetic differences caused by the shank BSP differences that were the largest contributors to the hip variations. Finally, BSP differences produced larger kinetic differences for the subject with larger segment masses, suggesting that parameter accuracy is more important for studies focused on overweight populations. The new image-based BSP estimation method described in this paper addressed the limitations of currently used geometric and regression methods by using exact limb geometry to determine subject-specific parameters. BSP differences have the largest effect on kinetic analyses of motions with large limb accelerations, for joints farther along the kinematic chain from the known forces and moments, and for subjects with larger limb masses or BMIs.

  View details for DOI 10.1115/1.4000155

  View details for Web of Science ID 000274106900004

  View details for PubMedID 20524742

• Vibration training intervention to maintain cartilage thickness and serum concentrations of cartilage oligometric matrix protein (COMP) during immobilization OSTEOARTHRITIS AND CARTILAGE Liphardt, A., Muendermann, A., Koo, S., Baecker, N., Andriacchi, T. P., Zange, J., Mester, J., Heer, M. 2009; 17 (12): 1598-1603

  Abstract

  To test the hypotheses that 1) 14-days of immobilization of young healthy subjects using a 6 degrees -"head-down-tilt-bed-rest"-model (6 degrees -HDT) would reduce cartilage thickness in the knee and serum Cartilage oligometric matrix protein (COMP) concentration and 2) isolated whole body vibration training would counteract the bed rest effects.The study was performed and designed in compliance with the Declaration of Helsinki and is registered as trial DRKS00000140 in the German Clinical Trial Register (register.germanctr.de). Eight male healthy subjects (78.0+/-9.5kg; 179+/-0.96cm, 26+/-5 years) performed 14 days of 6 degrees -HDT. The study was designed as a cross-over-design with two study phases: a training and a control intervention. During the training intervention, subjects underwent 2x5-min whole body vibration training/day (Frequency: 20Hz; amplitude: 2-4mm). Magnetic resonance (MR) images (slice thickness: 2mm; in-plane resolution: 0.35x0.35mm; pixels: 448x512) were taken before and after the 6 degrees -HDT periods. Average cartilage thicknesses were calculated for the load bearing regions on the medial and lateral articulating surfaces in the femur and tibia.While the control intervention resulted in an overall loss in average cartilage thickness of -8% (pre: 3.08mm+/-0.6mm post: 2.82mm+/-0.6mm) in the weight-bearing regions of the tibia, average cartilage thickness increased by 21.9% (pre: 2.66mm+/-0.45mm post: 3.24mm+/-0.63mm) with the vibration intervention. No significant differences were found in the weight-bearing regions of the femur. During both interventions, reduced serum COMP concentrations were observed (control intervention: -13.6+/-8.4%; vibration intervention: -9.9+/-3.3%).The results of this study suggest that articular cartilage thickness is sensitive to unloading and that vibration training may be a potent countermeasure against these effects. The sensitivity of cartilage to physical training is of high relevance for training methods in space flight, elite and sport and rehabilitation after illness or injury.

  View details for DOI 10.1016/j.joca.2009.07.007

  View details for Web of Science ID 000272966700011

  View details for PubMedID 19747585

• Accuracy of 3D Cartilage Models Generated From MR Images Is Dependent on Cartilage Thickness: Laser Scanner Based Validation of In Vivo Cartilage JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME Koo, S., Giori, N. J., Gold, G. E., Dyrby, C. O., Andriacchi, T. P. 2009; 131 (12)

  Abstract

  Cartilage morphology change is an important biomarker for the progression of osteoarthritis. The purpose of this study was to assess the accuracy of in vivo cartilage thickness measurements from MR image-based 3D cartilage models using a laser scanning method and to test if the accuracy changes with cartilage thickness. Three-dimensional tibial cartilage models were created from MR images (in-plane resolution of 0.55 mm and thickness of 1.5 mm) of osteoarthritic knees of ten patients prior to total knee replacement surgery using a semi-automated B-spline segmentation algorithm. Following surgery, the resected tibial plateaus were laser scanned and made into 3D models. The MR image and laser-scan based models were registered to each other using a shape matching technique. The thicknesses were compared point wise for the overall surface. The linear mixed-effects model was used for statistical test. On average, taking account of individual variations, the thickness measurements in MRI were overestimated in thinner (<2.5 mm) regions. The cartilage thicker than 2.5 mm was accurately predicted in MRI, though the thick cartilage in the central regions was underestimated. The accuracy of thickness measurements in the MRI-derived cartilage models systemically varied according to native cartilage thickness.

  View details for DOI 10.1115/1.4000087

  View details for Web of Science ID 000273614400004

  View details for PubMedID 20524727

  View details for PubMedCentralID PMC3072833

• Changes in running kinematics and kinetics in response to a rockered shoe intervention CLINICAL BIOMECHANICS Boyer, K. A., Andriacchi, T. P. 2009; 24 (10): 872-876

  Abstract

  A suggested link between ambulatory mechanics and injury development has resulted in significant interest the development of footwear to change locomotion patterns. The purpose of this study was to test the hypothesis that there will be significant changes in the kinematics and kinetics at the ankle and minimal changes at the knee and hip in the mechanics of running in a shoe with a sagittal plane curvature relative to a flat soled shoe.During running 3-D lower extremity kinematics and kinetics for 19 healthy volunteers were quantified using an optoelectronics system and a force plate. Data were collected for a flat sole conventional shoe (New Balance 658 (Control)) and a shoe with a rounded sole in the sagittal plane (Masai Barefoot Technologies (MBT)). Data were compared for the two shoe conditions using paired Student t-tests (alpha=0.05).The ankle dorsi-flexion angles at heel-strike and mid-stance were greater, while the ankle plantar and dorsi-flexion moments and peak ankle joint power were significantly lower with the MBT relative to the control (P<0.05). Decreases in the first medial GRF peak and the peak anterior GRF peak were also found for running in the MBT shoe.Despite a major difference in sole geometry, accommodations to the rockered sole were found only at the ankle. These results suggest changes in ankle kinematics and kinetics may be used to minimize the effect of changes in sole rocker on limb dynamics. Thus, changes in shoe rocker may offer potential therapeutic opportunities for running related conditions at the ankle without substantial risk to the knee or hip.

  View details for DOI 10.1016/j.clinbiomech.2009.08.003

  View details for Web of Science ID 000271784700014

  View details for PubMedID 19744753

• Change in Serum COMP Concentration Due to Ambulatory Load Is Not Related to Knee OA Status JOURNAL OF ORTHOPAEDIC RESEARCH Muendermann, A., King, K. B., Smith, L., Andriacchi, T. P. 2009; 27 (11): 1408-1413

  Abstract

  The aim of this study was to test the hypothesis that a change in serum cartilage oligomeric matrix protein (COMP) concentration is related to joint load during a 30-min walking exercise in patients with medial compartment knee osteoarthritis (OA) and in age-matched control subjects. Blood samples were drawn from 42 patients with medial compartment knee OA and from 41 healthy age-matched control subjects immediately before, immediately after, and 0.5, 1.5, 3.5, and 5.5 h after a 30-min walking exercise on a level outdoor walking track at self-selected normal speed. Serum COMP concentrations were determined using a commercial ELISA. Basic time-distance gait variables were recorded using an activity monitor. Joint loads were measured using gait analysis. Serum COMP concentrations increased immediately after the walking exercise (+6.3% and +5.6%; p < 0.001) and decreased over 5.5 h after the exercise (-11.1% and -14.6%; p < 0.040 and p = 0.001) in patients and control subjects, respectively. The magnitude of increase in COMP concentration did not differ between groups (p = 0.902) and did not correlate with any variables describing ambulatory loads at the joints of the lower extremity. These results, taken together with a previous study of a younger healthy population, suggest the possibility that the influence of ambulatory loads on cartilage turnover is dependent on age.

  View details for DOI 10.1002/jor.20908

  View details for Web of Science ID 000271310700002

  View details for PubMedID 19422040

• Graft Orientation Influences the Knee Flexion Moment During Walking in Patients With Anterior Cruciate Ligament Reconstruction AMERICAN JOURNAL OF SPORTS MEDICINE Scanlan, S. F., Blazek, K., Chaudhari, A. M., Safran, M. R., Andriacchi, T. P. 2009; 37 (11): 2173-2178

  Abstract

  Anterior cruciate ligament graft orientation has been proposed as a potential mechanism for failure of single-bundle anterior cruciate ligament reconstruction and has been considered important in the restoration of normal ambulatory knee mechanics.To evaluate the possibility that patients adapt their mechanics of walking to the orientation of the anterior cruciate ligament graft. This was determined by testing the hypothesis that peak external knee flexion moment (net quadriceps moment) during walking in patients with anterior cruciate ligament reconstruction is correlated with coronal and sagittal anterior cruciate ligament graft orientations.Cross-sectional study; Level of evidence, 3.Gait analysis was performed to assess dynamic knee function during walking in 17 subjects with unilateral anterior cruciate ligament reconstructions. Magnetic resonance imaging was used to measure coronal and sagittal anterior cruciate ligament graft orientations.A negative correlation was observed between peak external knee flexion moment during walking and coronal angle of the anterior cruciate ligament graft (1.0 m/s walking speed, r = -0.87, P < .001; 1.3 m/s, r = -0.66, P = .004; 1.6 m/s, r = -0.24, P > .05); no correlation was found with the sagittal graft angle (1.0 m/s walking speed, r = 0.21, P > .05; 1.3 m/s, r = 0.20, P > .05; 1.6 m/s, r = 0.13, P > .05).The negative correlation between peak external knee flexion moment during walking and the coronal angle of the anterior cruciate ligament graft indicates that as the anterior cruciate ligament graft is placed in a more vertical coronal orientation, patients reduce their net quadriceps usage during walking.This finding supports the hypothesis that graft placement plays a critical role in the restoration of normal ambulatory mechanics after anterior cruciate ligament reconstruction and thus could provide a partial explanation for the increased incidence of premature osteoarthritis at long-term follow-up in patients with anterior cruciate ligament reconstruction.

  View details for DOI 10.1177/0363546509339574

  View details for Web of Science ID 000271216600012

  View details for PubMedID 19729363

• Central and peripheral region tibial plateau chondrocytes respond differently to in vitro dynamic compression OSTEOARTHRITIS AND CARTILAGE Bevill, S. L., Briant, P. L., Levenston, M. E., Andriacchi, T. P. 2009; 17 (8): 980-987

  Abstract

  The objective of this study was to test the hypotheses that chondrocytes from distinct regions of the porcine tibial plateau: (1) display region-specific baseline gene expression, and (2) respond differently to in vitro mechanical loading.Articular cartilage explants were obtained from central (not covered by meniscus) and peripheral (covered by meniscus) regions of porcine tibial plateaus. For baseline gene expression analysis, samples were snap frozen. To determine the effect of mechanical loading, central and peripheral region explants were exposed to equivalent dynamic compression (0-100 kPa) and compared to site-matched free-swelling controls (FSCs). mRNA levels for type II collagen (CII), aggrecan (AGGR), matrix metalloproteinase 1 (MMP-1), MMP-3, MMP-13, A disintegrin and metalloproteinase with thrombospondin motifs 4 (ADAM-TS4), ADAM-TS5, tissue inhibitor of metalloproteinases 1 (TIMP-1), TIMP-2, and tumor necrosis factor alpha (TNFalpha) were quantified using real time polymerase chain reaction (RT-PCR).At baseline, mRNA levels for the structural proteins CII and AGGR were approximately twofold greater in the central region compared with peripheral region explants. In vitro dynamic compression strongly affected expression levels for CII, AGGR, MMP-3, and TIMP-2 relative to FSCs. Response differed significantly by region, with greater upregulation of CII, AGGR, and MMP-3 in central region explants.Chondrocytes from different regions of the porcine tibial plateau express mRNA for structural proteins at different levels and respond to equivalent in vitro mechanical loading with distinctive changes in gene expression. These regional biological variations appear to be related to the local mechanical environment in the normal joint, and thus may indicate a sensitivity of the joint to conditions that alter joint loading such as anterior cruciate ligament (ACL) injury, meniscectomy, or joint instability.

  View details for DOI 10.1016/j.joca.2008.12.005

  View details for Web of Science ID 000268654700003

  View details for PubMedID 19157913

• Influence of Patellar Ligament Insertion Angle on Quadriceps Usage during Walking in Anterior Cruciate Ligament Reconstructed Subjects JOURNAL OF ORTHOPAEDIC RESEARCH Shin, C. S., Chaudhari, A. A., Dyrby, C. O., Andriacchi, T. P. 2009; 27 (6): 730-735

  Abstract

  Reduced quadriceps contraction has been suggested as an adaptation to prevent anterior tibial translation in anterior cruciate ligament (ACL)-deficient knees. This theory has been supported by a recent study that peak knee flexion moment (thought to be created by a decrease of quadriceps contraction) during walking was negatively correlated with patellar ligament insertion angle (PLIA) in ACL-deficient knees, but not in contralateral, uninjured knees. In addition, the PLIA was significantly smaller in ACL-deficient knees than in contralateral, uninjured knees. However, it is unknown whether ACL reconstruction restores the PLIA or whether the relationship between the PLIA and knee flexion moments previously observed in ACL-deficient knees disappears. This study tested the following hypotheses: (1) The PLIA of ACL-reconstructed knees is significantly smaller than the PLIA of uninjured contralateral knees; (2) Peak knee flexion moment (balanced by net quadriceps moment) during walking is negatively correlated with the PLIA in ACL-reconstructed knees. The PLIA of 24 ACL-reconstructed and contralateral knees were measured using MRI, and peak knee flexion moments during walking were measured. Results showed that the PLIA of ACL-reconstructed (22.9 +/- 4.4 degrees) knees was not significantly smaller (p = 0.09, power = 0.99) than the PLIA of contralateral (24.1 +/- 4.8 degrees) knees. Peak knee flexion moment was not correlated with the PLIA following ACL reconstruction (R2 = 0.016, power = 0.99). However, the magnitude of the knee flexion moment remained significantly lower in ACL-reconstructed knees. In summary, this study has shown that the PLIA of ACL-reconstructed knees returned to normal and that patients no longer adapt their gait in response to the PLIA, though quadriceps function did not return to normal levels.

  View details for DOI 10.1002/jor.20806

  View details for Web of Science ID 000266123100005

  View details for PubMedID 19025774

• Adaptive Patterns of Movement during Stair Climbing in Patients with Knee Osteoarthritis JOURNAL OF ORTHOPAEDIC RESEARCH Asay, J. L., Muendermann, A., Andriacchi, T. P. 2009; 27 (3): 325-329

  Abstract

  The purpose of this study was to determine if there is a distinctive characteristic in the pattern of movement (forward trunk lean to reduce demand on the quadriceps muscle) during stair climbing in patients with knee osteoarthritis (OA) that is associated with the severity of the disease. Twenty-three patients with radiographically diagnosed knee OA and 20 physically active adults performed stair ascending trials without support at their self-selected speed. Standard gait analysis was used to calculate three-dimensional lower extremity joint kinematics and kinetics. Forward trunk lean, or trunk flexion, was defined as the sagittal plane projection of the angle between a line connecting the midpoint of the trans-acromion line and the midpoint of the trans-iliac crest line and the global vertical axis. Patients with more severe knee OA (KL >or= 3) had greater forward trunk lean (+6.3 degrees , p = 0.045) and lower knee net quadriceps moments (-35.2%, p = 0.001) than controls. In more severe patients, the forward trunk lean was correlated with a reduction in the net quadriceps moment during stair climbing (R(2) = 0.590, p = 0.006). The results of this study identified a distinctive compensatory pattern of movement to reduce the quadriceps demand during stair climbing in patients with more severe knee OA by increasing forward trunk lean. Assessing forward trunk lean during stair climbing may be a useful functional marker for evaluating osteoarthritis status and quadriceps function that appears to be a more sensitive indicator of disease severity than perceived pain.

  View details for DOI 10.1002/jor.20751

  View details for Web of Science ID 000263307200007

  View details for PubMedID 18853434

• Posturographic analysis through markerless motion capture without ground reaction forces measurement JOURNAL OF BIOMECHANICS Corazza, S., Andriacchi, T. R. 2009; 42 (3): 370-374

  Abstract

  The ability of the central nervous system to control posture and balance has been used with increasing frequency for the diagnosis and/or treatment evaluation of various neuromuscular diseases. Typically this analysis (Posturographic Analysis) is based on tracking the motion of the center of mass (COM) during quiet standing, however direct measurement of the COM has been commonly approximated using the movement of the center of pressure (COP). The purpose of this study was to apply and validate a new method to track the COM (center of mass) and COP (center of pressure) from a visual hull measured using a markerless motion capture (MMC) method. The method was tested by comparing the calculation of the COP from direct measurements of the COP. The deviations between the methods, below 2mm, were small relative to the average range of movement guaranteeing a satisfactory signal to noise ratio. This new method requires only kinematic data through MMC method and without the need of a force plate can identify the influence of individual body segments to motion of the COM.

  View details for DOI 10.1016/j.jbiomech.2008.11.019

  View details for Web of Science ID 000263657600029

  View details for PubMedID 19147143

• The effect of isolated valgus moments on ACL strain during single-leg landing: A simulation study JOURNAL OF BIOMECHANICS Shin, C. S., Chaudhari, A. M., Andriacchi, T. P. 2009; 42 (3): 280-285

  Abstract

  Valgus moments on the knee joint during single-leg landing have been suggested as a risk factor for anterior cruciate ligament (ACL) injury. The purpose of this study was to test the influence of isolated valgus moment on ACL strain during single-leg landing. Physiologic levels of valgus moments from an in vivo study of single-leg landing were applied to a three-dimensional dynamic knee model, previously developed and tested for ACL strain measurement during simulated landing. The ACL strain, knee valgus angle, tibial rotation, and medial collateral ligament (MCL) strain were calculated and analyzed. The study shows that the peak ACL strain increased nonlinearly with increasing peak valgus moment. Subjects with naturally high valgus moments showed greater sensitivity for increased ACL strain with increased valgus moment, but ACL strain plateaus below reported ACL failure levels when the applied isolated valgus moment rises above the maximum values observed during normal cutting activities. In addition, the tibia was observed to rotate externally as the peak valgus moment increased due to bony and soft-tissue constraints. In conclusion, knee valgus moment increases peak ACL strain during single-leg landing. However, valgus moment alone may not be sufficient to induce an isolated ACL tear without concomitant damage to the MCL, because coupled tibial external rotation and increasing strain in the MCL prevent proportional increases in ACL strain at higher levels of valgus moment. Training that reduces the external valgus moment, however, can reduce the ACL strain and thus may help athletes reduce their overall ACL injury risk.

  View details for DOI 10.1016/j.jbiomech.2008.10.031

  View details for Web of Science ID 000263657600013

  View details for PubMedID 19100550

  View details for PubMedCentralID PMC2663630

• Gait Mechanics Influence Healthy Cartilage Morphology and Osteoarthritis of the Knee Annual Meeting of the American-Academy-of-Orthopaedic-Surgeons/Orthopaedic-Research-Society Andriacchi, T. P., Koo, S., Scanlan, S. F. JOURNAL BONE JOINT SURGERY INC. 2009: 95–101

  View details for DOI 10.2106/JBJS.H.01408

  View details for Web of Science ID 000263243000023

• STEP-TO-STEP VARIABILITY IN TIBIOFEMORAL CONTACT FORCE DURING WALKING MEASURED BY AN INSTRUMENTED KNEE IMPLANT ASME Summer Bioengineering Conference Scanlan, S. F., D'Lima, D. D., Colwell, C. W., Andriacchi, T. P. AMER SOC MECHANICAL ENGINEERS. 2009: 907–908

  View details for Web of Science ID 000280089000454

• TENSION BANDS PLACED ON THE THIGH AND SHANK PRODUCE CHANGES IN THE KNEE FLEXION MOMENT AND GAIT ASYMMETRY ASME Summer Bioengineering Conference Dowling, A. V., Fenner, N., Andriacchi, T. P. AMER SOC MECHANICAL ENGINEERS. 2009: 979–980

  View details for Web of Science ID 000280089000490

• REDUCTION IN THE MEDIAL COMPARTMENT FORCE CORRELATES WITH THE REDUCTION IN KNEE ADDUCTION MOMENT USING A VARIABLE-STIFFNESS SHOE WITH AN INSTRUMENTED KNEE ASME Summer Bioengineering Conference Erhart, J. C., Dyrby, C., D'Lima, D. D., Colwell, C. W., Andriacchi, T. P. AMER SOC MECHANICAL ENGINEERS. 2009: 937–938

  View details for Web of Science ID 000280089000469

• MENISCAL MOVEMENT DURING THE GAIT CYCLE IS SENSITIVE TO THE ATTACHMENT PROPERTIES OF THE MENISCAL HORNS ASME Summer Bioengineering Conference Netravali, N. A., Giori, N. J., Andriacchi, T. P. AMER SOC MECHANICAL ENGINEERS. 2009: 981–982

  View details for Web of Science ID 000280089000491

• REGIONAL CARTILAGE THINNING OCCURS FIRST IN THE WALKING WEIGHT BEARING REGIONS OF THE FEMUR IN MEDIAL COMPARTMENT KNEE OSTEOARTHRITIS ASME Summer Bioengineering Conference Erhart, J. C., Muendermann, A., Koo, S., Merrick, B., Deagon, A., Giori, N. J., Andriacchi, T. P. AMER SOC MECHANICAL ENGINEERS. 2009: 835–836

  View details for Web of Science ID 000263364700418

• COMPARISON OF NUMERICALLY MODELED KNEE JOINT CONTACT FORCES TO INSTRUMENTED TOTAL KNEE PROSTHESIS FORCES ASME Summer Bioengineering Conference Lundberg, H. J., Foucher, K. C., Andriacchi, T. P., Wimmer, M. A. AMER SOC MECHANICAL ENGINEERS. 2009: 379–380

  View details for Web of Science ID 000280089000190

• REGIONAL VARIATIONS IN CARTILAGE MECHANICS AND COMPOSITION SUGGEST A SENSITIVITY TO CHANGES IN CHRONIC JOINT LOADING PATTERNS ASME Summer Bioengineering Conference Bevill, S. L., Andriacchi, T. P. AMER SOC MECHANICAL ENGINEERS. 2009: 279–280

  View details for Web of Science ID 000280089000140

• CHANGES IN TIBIOFEMORAL KINEMATICS AND KINETICS DURING STAIR ASCENT AFTER PARTIAL MEDIAL MENISCECTOMY ASME Summer Bioengineering Conference Netravali, N. A., Andriacchi, T. P. AMER SOC MECHANICAL ENGINEERS. 2009: 813–814

  View details for Web of Science ID 000263364700407

• ASSESSING THE APPROPRIATE NUMBER OF DAYS NEEDED TO APPROXIMATE PHYSICAL ACTIVITY LEVEL IN THE ACTIVE ELDERLY ASME Summer Bioengineering Conference Rylander, J. H., Boyer, K. A., Andriacchi, T. P., Beaupre, G. S. AMER SOC MECHANICAL ENGINEERS. 2009: 1101–1102

  View details for Web of Science ID 000280089000551

• A RIGID BODY AND SPRING MODEL OF THE LUMBAR SPINE WHICH CONSIDERS THE MECHANICAL LOADS AT THE BONE-SCREW INTERFACE ASME Summer Bioengineering Conference Kiriyama, Y., Matsumoto, M., Toyama, Y., Andriacchi, T. P., Nagura, T. AMER SOC MECHANICAL ENGINEERS. 2009: 1241–1242

  View details for Web of Science ID 000280089000621

• AN AUTOMATED IMAGE-BASED METHOD OF 3D SUBJECT SPECIFIC BODY SEGMENT PARAMETER ESTIMATION ASME Summer Bioengineering Conference Sheets, A. L., Corazza, S., Andriacchi, T. AMER SOC MECHANICAL ENGINEERS. 2009: 857–858

  View details for Web of Science ID 000263364700429

• INTER-SUBJECT VARIABILITY IN GROUND REACTION FORCE - WALKING SPEED RELATIONSHIP IS RELATED TO DIFFERENT MOTION OF THE CENTER OF MASS ASME Summer Bioengineering Conference Boyer, K., Rylander, J., Andriacchi, T., Beaupre, G. AMER SOC MECHANICAL ENGINEERS. 2009: 31–32

  View details for Web of Science ID 000280089000016

• DYNAMIC COMPRESSION IN THE PRESENCE OF TNF-ALPHA DIFFERENTIALLY EFFECTS GENE EXPRESSION IN TIBIAL PLATEAU CARTILAGE COVERED AND UNCOVERED BY THE MENISCUS ASME Summer Bioengineering Conference Bevill, S. L., Andriacchi, T. P. AMER SOC MECHANICAL ENGINEERS. 2009: 815–816

  View details for Web of Science ID 000263364700408

• KINEMATIC DIFFERENCES BETWEEN THE FLAT, KICK AND SLICE SERVES MEASURED USING A MARKERLESS MOTION CAPTURE METHOD ASME Summer Bioengineering Conference Sheets, A. L., Corazza, S., Abrams, G., Safran, M., Andriacchi, T. AMER SOC MECHANICAL ENGINEERS. 2009: 195–196

  View details for Web of Science ID 000280089000098

• Gender differences exist in the hip joint moments of healthy older walkers JOURNAL OF BIOMECHANICS Boyer, K. A., Beaupre, G. S., Andriacchi, T. P. 2008; 41 (16): 3360-3365

  Abstract

  Gender differences in the incidence of symptomatic hip osteoarthritis (OA), changes in hip cartilage volume and hip joint space and rates hip arthroplasty of older people are reported in the literature. As the rate of progression of OA is in part mechanically modulated it is possible that this gender bias may be related to inherent differences (if they exist) in walking mechanics between older males and females. The purpose of this study was to examine potential mechanisms for gender differences in hip joint mechanics during walking by testing the hypotheses that females would exhibit higher hip flexion, adduction and internal rotation moments but not significantly greater normalized ground reaction forces (GRFs). Forty-two healthy subjects (21 male, 21 female), ages 50-79yr were recruited for gait analysis. In support of the hypotheses, greater external hip adduction and internal rotation along with hip extension moments were found for females compared to males after normalizing for body size for all self-selected walking speeds. Differences in walking style (kinematics) were the main determinants in the joint kinetic differences as no differences in the normalized GRFs were found. As external joint moments are surrogate measures of the joint contact forces, the results of this study suggest the hip joint stress for the female population is higher compared to male population. This is in favor of a hypothesis that the increased joint contact stress in a female population could contribute to a greater joint degeneration at the hip in females as compared with males.

  View details for DOI 10.1016/j.jbiomech.2008.09.030

  View details for Web of Science ID 000261965300010

  View details for PubMedID 19022448

• A comparison of measuring mechanical axis alignment using three-dimensional position capture with skin markers and radiographic measurements in patients with bilateral medial compartment knee osteoarthritis KNEE Muendermann, A., Dyrby, C. O., Andriacchi, T. P. 2008; 15 (6): 480-485

  Abstract

  The mechanical axis alignment of the lower extremity is typically measured from frontal plane radiographs of the entire lower extremity during double support standing. The purpose of this study was to test the hypothesis that the mechanical axis alignment can be predicted from skin markers on anatomical landmarks and anthropometric measurements and a stereophotogrammetric system based on significant correlation with the mechanical axis alignment measured from standing radiographs. Mechanical axis alignment was measured using full-limb radiographs for both knees of 62 patients with bilateral medial compartment knee osteoarthritis (OA). Mechanical axis alignment was also measured using a stereophotogrammetric system with markers on anatomical landmarks and anthropometric measurements to determine joint centers. The mechanical axis alignment from position capture correlated with that from radiographs (R(2)=0.544; P<0.001). This relationship did not depend on age, gender, BMI, or OA severity. A small but significant difference in the mechanical axis alignment between the two methods was observed (radiograph: 2.6 varus; position capture: 3.8 varus; P=0.001). Associations between mechanical axis alignment and OA severity were found for both methods (radiographic: R(2)=0.563; position capture: R(2)=0.807). The proposed method allows the measurement of the mechanical axis alignment without exposure to radiation. This method enables the establishment of the relationship between lower limb alignment and functional variables such as dynamic joint loading in degenerative joint disease and joint injury even in populations who typically do not undergo radiographic examination.

  View details for DOI 10.1016/j.knee.2008.07.002

  View details for Web of Science ID 000261547700009

  View details for PubMedID 18762426

• Predicting changes in knee adduction moment due to load-altering interventions from pressure distribution at the foot in healthy subjects JOURNAL OF BIOMECHANICS Erhart, J. C., Muendermann, A., Muendermann, L., Andriacchi, T. P. 2008; 41 (14): 2989-2994

  Abstract

  The purpose of this pilot study of healthy subjects was to determine if changes in foot pressure patterns associated with a lateral wedge can predict the changes in the knee adduction moment. We tested two hypotheses: (1) increases or decreases in the knee adduction moment and ankle eversion moment due to load-altering footwear interventions can be predicted from foot pressure distribution and (2) changes in magnitude of the knee adduction moment and ankle eversion moment due to lateral wedges can be predicted from pressure distribution at the foot during walking. Fifteen healthy adults performed walking trials in three shoes: 0 degrees , 4 degrees , and 8 degrees laterally wedged. Maximum heel pressure ratio, first peak knee adduction moment, and peak ankle eversion moment were assessed using a pressure mat, motion capture system, and force plate. Increases or decreases in the knee adduction moment and ankle eversion moment were predicted well from foot pressure distribution. However, the magnitude of the pressure change did not predict the magnitude of the peak knee adduction moment change or peak ankle eversion moment change. Factors such as limb alignment or trunk motion may affect the knee adduction moment and override a direct relationship between the pressure distribution at the shoe-ground interface and the load distribution at the knee. However, changes (increases or decreases) in the peak knee adduction moment due to load-altering footwear interventions predicted from pressure distribution during walking can be important when evaluating these types of interventions from a clinical perspective.

  View details for DOI 10.1016/j.jbiomech.2008.07.021

  View details for Web of Science ID 000260985700014

  View details for PubMedID 18771767

• In vivo knee loading characteristics during activities of daily living as measured by an instrumented total knee replacement JOURNAL OF ORTHOPAEDIC RESEARCH Muendermann, A., Dyrby, C. O., D'Lima, D. D., Colwell, C. W., Andriacchi, T. P. 2008; 26 (9): 1167-1172

  Abstract

  We examined the relationship between activity, peak load, medial to lateral load distribution, and flexion angle at peak load for activities of daily living. An instrumented knee prosthesis was used to measure knee joint force simultaneously with motion capture during walking, chair sit to stand and stand to sit, stair ascending and descending, squatting from a standing position, and golf swings. The maximum total compressive load at the knee was highest during stair ascending and descending and lowest during rising from a chair. Maximum total compressive load occurred at substantially different flexion angles ranging from 8.5 degrees during walking to 91.8 degrees during squatting. For all activities, total compressive load exceeded 2 times body weight, and for most activities 2.5 times body weight. Most activities placed a greater load on the medial compartment than the lateral compartment. Activities were grouped into three categories: high cycle loading (walk), high load (stair ascent, descent, and golf), and high flexion angle (chair sit to stand/stand to sit, and squat). The results demonstrate that the forces and motion sustained by the knee are highly activity-dependent and that the unique loading characteristics for specific activities should be considered for the design of functional and robust total knee replacements, as well as for rehabilitation programs for patients with knee osteoarthritis or following total knee arthroplasty.

  View details for DOI 10.1002/jor.20655

  View details for Web of Science ID 000258240300001

  View details for PubMedID 18404700

• A variable-stiffness shoe lowers the knee adduction moment in subjects with symptoms of medial compartment knee osteoarthritis. Journal of biomechanics Erhart, J. C., Mündermann, A., Elspas, B., Giori, N. J., Andriacchi, T. P. 2008; 41 (12): 2720-2725

  Abstract

  The purpose of this study was to evaluate the effectiveness of variable-stiffness shoes in lowering the peak external knee adduction moment during walking in subjects with symptomatic medial compartment knee osteoarthritis. The influence on other lower extremity joints was also investigated. The following hypotheses were tested: (1) variable-stiffness shoes will lower the knee adduction moment in the symptomatic knee compared to control shoes; (2) reductions in knee adduction moment will be greater at faster speeds; (3) subjects with higher initial knee adduction moments in control shoes will have greater reductions in knee adduction moment with the intervention shoes; and (4) variable-stiffness shoes will cause secondary changes in the hip and ankle frontal plane moments. Seventy-nine individuals were tested at self-selected slow, normal, and fast speeds with a constant-stiffness control shoe and a variable-stiffness intervention shoe. Peak moments for each condition were assessed using a motion capture system and force plate. The intervention shoes reduced the peak knee adduction moment compared to control at all walking speeds, and reductions increased with increasing walking speed. The magnitude of the knee adduction moment prior to intervention explained only 11.9% of the variance in the absolute change in maximum knee adduction moment. Secondary changes in frontal plane moments showed primarily reductions in other lower extremity joints. This study showed that the variable-stiffness shoe reduced the knee adduction moment in subjects with medial compartment knee osteoarthritis without the discomfort of a fixed wedge or overloading other joints, and thus can potentially slow the progression of knee osteoarthritis.

  View details for DOI 10.1016/j.jbiomech.2008.06.016

  View details for PubMedID 18675981

• Variable-stiffness shoe lowers the knee adduction moment in subjects with symptoms of medial compartment knee osteoarthritis JOURNAL OF BIOMECHANICS Erhart, J. C., Muendermann, A., Elspas, B., Giori, N. J., Andriacchi, T. P. 2008; 41 (12): 2720-2725

  Abstract

  The purpose of this study was to evaluate the effectiveness of variable-stiffness shoes in lowering the peak external knee adduction moment during walking in subjects with symptomatic medial compartment knee osteoarthritis. The influence on other lower extremity joints was also investigated. The following hypotheses were tested: (1) variable-stiffness shoes will lower the knee adduction moment in the symptomatic knee compared to control shoes; (2) reductions in knee adduction moment will be greater at faster speeds; (3) subjects with higher initial knee adduction moments in control shoes will have greater reductions in knee adduction moment with the intervention shoes; and (4) variable-stiffness shoes will cause secondary changes in the hip and ankle frontal plane moments. Seventy-nine individuals were tested at self-selected slow, normal, and fast speeds with a constant-stiffness control shoe and a variable-stiffness intervention shoe. Peak moments for each condition were assessed using a motion capture system and force plate. The intervention shoes reduced the peak knee adduction moment compared to control at all walking speeds, and reductions increased with increasing walking speed. The magnitude of the knee adduction moment prior to intervention explained only 11.9% of the variance in the absolute change in maximum knee adduction moment. Secondary changes in frontal plane moments showed primarily reductions in other lower extremity joints. This study showed that the variable-stiffness shoe reduced the knee adduction moment in subjects with medial compartment knee osteoarthritis without the discomfort of a fixed wedge or overloading other joints, and thus can potentially slow the progression of knee osteoarthritis.

  View details for DOI 10.1016/j.jbiomech.2008.06.016

  View details for Web of Science ID 000259552700018

• Knee kinematics, cartilage morphology, and osteoarthritis after ACL injury MEDICINE AND SCIENCE IN SPORTS AND EXERCISE Chaudhari, A. M., Briant, P. L., Bevill, S. L., Koo, S., Andriacchi, T. P. 2008; 40 (2): 215-222

  Abstract

  This review examines a mechanism for the initiation of osteoarthritis after anterior cruciate ligament (ACL) injury by considering the relationship between reported ambulatory changes after ACL injury, cartilage adaptation to load, and the association between cartilage loads during walking and regional variations in cartilage structure and biology. Taken together, these observations suggest that cartilage degeneration after ACL injury could be caused by a kinematic gait change that shifts ambulatory loading applied to cartilage. Such a shift may cause regions of cartilage to become newly loaded, be subjected to altered levels of compression and tension, or become unloaded. The metabolic sensitivity of chondrocytes to such changes in their mechanical environment, combined with the low adaptation potential of mature cartilage, could lead to cartilage degeneration and premature osteoarthritis after ACL injury. This proposed mechanism demonstrates the value of using the ACL injury model to understand the relationship between mechanics and biology, as well as helping to explain the importance of restoring normal ambulatory kinematics after ACL injury to avoid premature osteoarthritis.

  View details for DOI 10.1249/mss.0b013e31815cbb0e

  View details for Web of Science ID 000252608300005

  View details for PubMedID 18202582

• The knee joint center of rotation is predominantly on the lateral side during normal walking JOURNAL OF BIOMECHANICS Koo, S., Andriacchi, T. P. 2008; 41 (6): 1269-1273

  Abstract

  The purpose of this study was to test the hypothesis of whether the center of rotation (COR) in the transverse plane of the knee is in the medial side during normal walking in a manner similar to that previously described during non-ambulatory activities. The kinematics for normal knees was obtained from 46 knees during normal walking using the point cluster technique. The COR of the medial-lateral axis of the femur relative to the tibia was determined during the stance phase of walking. The hypothesis that the COR is in the medial side during stance was not supported by this study. The average COR during the stance phase of walking was in the lateral compartment for all 46 knees. In addition, the instantaneous COR occurred on the medial side on average <25% of the time during the stance phase. Thus, while the COR is predominantly on the lateral side of the knee during walking, the normal function of the knee during walking is associated with both lateral and medial pivoting. These results also demonstrate the importance of describing knee kinematics in the context of a specific activity or the constraints of the test conditions.

  View details for Web of Science ID 000255674700015

  View details for PubMedID 18313060

• Implications of increased medio-lateral trunk sway for ambulatory mechanics JOURNAL OF BIOMECHANICS Muendermann, A., Asay, J. L., Muendermann, L., Andriacchi, T. P. 2008; 41 (1): 165-170

  Abstract

  The purposes of this study was to test a mechanism to reduce the knee adduction moment by testing the hypothesis that increased medio-lateral trunk sway can reduce the knee adduction moment during ambulation in healthy subjects, and to examine the possibility that increasing medio-lateral trunk sway can produce similar potentially adverse secondary gait changes previously associated with reduced knee adduction moments in patients with knee osteoarthritis. Nineteen healthy adults performed walking trials with normal and increased medio-lateral trunk sway at a self-selected normal walking speed. Standard gait analysis was used to calculate three-dimensional lower extremity joint kinematics and kinetics. Knee and hip adduction moments were lower (-65.0% and -57.1%, respectively) for the increased medio-lateral trunk sway trials than for the normal trunk sway trials. Knee flexion angle at heel-strike was 3 degrees higher for the increased than for the normal trunk sway trials. Knee and hip abduction moments were higher for the increased medio-lateral trunk sway trials, and none of the other variables differed between the two conditions. Walking with increased medio-lateral trunk sway substantially reduces the knee adduction moment during walking in healthy subjects without some of the adverse secondary effects such as increased axial loading rates at the major joints of the lower extremity. This result supports the potential of using gait retraining for walking with increased medio-lateral trunk sway as treatment for patients with degenerative joint disease such as medial compartment knee osteoarthritis.

  View details for DOI 10.1016/j.jbiomech.2007.07.001

  View details for Web of Science ID 000253062100021

  View details for PubMedID 17678933

• The patella ligament insertion angle influences quadriceps usage during walking of anterior cruciate ligament deficient patients JOURNAL OF ORTHOPAEDIC RESEARCH Shin, C. S., Chaudhari, A. M., Dyrby, C. O., Andriacchi, T. P. 2007; 25 (12): 1643-1650

  Abstract

  Following ACL injury a reduction in the peak knee flexion moment during walking (thought to be created by a decrease of quadriceps contraction) has been described as an adaptation to reduce anterior tibial translation (ATT) relative to the femur. However, the amount of ATT caused by quadriceps contraction is influenced by the patellar ligament insertion angle (PLIA). The purpose of this study was to test the hypothesis that quadriceps usage during walking correlates to individual anatomical variations in the extensor mechanism as defined by PLIA. PLIA and gait were measured for ACL-deficient knees, using subjects' contralateral knees as controls. In ACL-deficient knees, PLIA was negatively correlated (R2 = 0.59) to peak knee flexion moment (balanced by net quadriceps moment), while no correlation was found in contralateral knees. Reduction in peak flexion moment in ACL-deficient knees compared to their contralateral knees was distinctive in subjects with large PLIA, possibly to avoid excessive ATT. These results suggest that subject-specific anatomic variability of knee extensor mechanism may account for the individual variability previously observed in adaptation to a quadriceps reduction strategy following ACL injury. The average (+/-1 SD) PLIA of ACL-deficient knees (21.1 +/- 3.4 degrees) was less than the average PLIA of contralateral knees (23.9 +/- 3.1 degrees). This altered equilibrium position of the tibiofemoral joint associated with reduced PLIA and adaptations of gait patterns following ACL injury may be associated with degenerative changes in the articular cartilage. In the future, individually tailored treatment and rehabilitation considering individuals' specific extensor anatomy may improve clinical outcomes.

  View details for Web of Science ID 000251179300013

  View details for PubMedID 17593539

• Knee and hip loading patterns at different phases in the menstrual cycle - Implications for the gender difference in anterior cruciate ligament injury rates AMERICAN JOURNAL OF SPORTS MEDICINE Chaudhari, A. M., Lindenfeld, T. N., Andriacchi, T. P., Hewett, T. E., Riccobene, J., Myer, G. D., Noyes, F. R. 2007; 35 (5): 793-800

  Abstract

  Menstrual cycle phase has been correlated with risk of noncontact anterior cruciate ligament injury in women. The mechanism by which hormonal cycling may affect injury rate is unknown.Jumping and landing activities performed during different phases of the menstrual cycle lead to differences in foot strike knee flexion, as well as peak knee and hip loads, in women not taking an oral contraceptive but not in women taking an oral contraceptive. Women will experience greater normalized joint loads than men during these activities.Controlled laboratory study.Twenty-five women (13 using oral contraceptives) and 12 men performed repeated trials of a horizontal jump, vertical jump, and drop from a 30-cm box on the left leg. Lower limb kinematics (foot strike knee flexion) and peak externally applied moments were calculated (hip adduction moment, hip internal rotation moment, knee flexion moment, knee abduction moment). Men were tested once. Women were tested twice for each phase of the menstrual cycle (follicular, luteal, ovulatory), as determined from serum analysis. An analysis of variance was used to examine differences between phases of the menstrual cycle and between groups (alpha = .05).No significant differences in moments or knee angle were observed between phases in either female group or between the 2 female groups or between either female group and the male controls.Variations of the menstrual cycle and the use of an oral contraceptive do not affect knee or hip joint loading during jumping and landing tasks.Because knee and hip joint loading is unaffected by cyclic variations in hormone levels, the observed difference in injury rates is more likely attributable to persistent differences in strength, neuromuscular coordination, or ligament properties.

  View details for DOI 10.1177/0363546506297537

  View details for Web of Science ID 000246264600013

  View details for PubMedID 17307891

• In healthy subjects without knee osteoarthritis, the peak knee adduction moment influences the acute effect of shoe interventions designed to reduce medial compartment knee load JOURNAL OF ORTHOPAEDIC RESEARCH Fisher, D. S., Dyrby, C. O., Mundermann, A., Morag, E., Andriacchi, T. P. 2007; 25 (4): 540-546

  Abstract

  The purpose of this study was to evaluate shoe sole material stiffness changes and angle changes that are intended to reduce the peak knee adduction moment during walking. Fourteen physically active adults were tested wearing their personal shoes (control) and five intervention pairs, two with stiffness variations, two with angle variations, and a placebo shoe. The intervention shoes were evaluated based on how much they reduced the peak knee adduction moment compared to the control shoe. An ANOVA test was used to detect differences between interventions. Linear regression analysis was used to determine a relationship between the magnitude of the knee adduction moment prior to intervention and the effectiveness of the intervention in reducing the peak knee adduction moment. Peak knee adduction moments were reduced for the altered stiffness and altered angle shoes (p < 0.010), but not for the placebo shoe (p = 0.363). Additionally, linear regression analysis showed that subjects with higher knee adduction moments prior to intervention had larger reductions in the peak knee adduction moment (p < 0.010). These results demonstrate that shoe sole stiffness and angle interventions can be used to reduce the peak knee adduction moment and that subjects with initially higher peak knee adduction moments have higher reductions in their peak knee adduction moments.

  View details for DOI 10.1002/jor.20157

  View details for Web of Science ID 000245063900015

  View details for PubMedID 17205556

• Clinical disability in posterior cruciate ligament deficient patients does not relate to knee laxity, but relates to dynamic knee function during stair descending KNEE SURGERY SPORTS TRAUMATOLOGY ARTHROSCOPY Iwata, S., Suda, Y., Nagura, T., Matsumoto, H., Otani, T., Andriacchi, T. P., Toyama, Y. 2007; 15 (4): 335-342

  Abstract

  We investigated the factors which influence clinical subjective symptoms during activities in Posterior cruciate ligament (PCL) deficient patients by evaluating knee laxity, muscle strength and knee mechanics during level walking, stair ascent and descent. Twenty-two subjects with isolated PCL deficient knees and 20 healthy volunteers were involved. The PCL deficient patients were divided into two subgroups based on previous history of experiencing giving-way during stair descent; a giving-way group (10 subjects) and a nongiving-way group (12 subjects). Giving-way during activities of daily living is a key symptom in isolated PCL deficient patients. No statistically significant differences in the knee laxity, muscle strength and knee mechanics during level walking and were observed between the giving-way group and the nongiving-way group. However, we found significant differences in the knee mechanics during stair ascent and descent between the two groups, and these differences were more remarkable during stair descent. Peak values of knee flexion angle, external knee flexion moment and posterior knee force during early stance phase were significantly lower in the giving-way group than in the nongiving-way group. This study indicated that the symptom of giving-way during stair descent was related to knee mechanics during stair descent, unlike other quantitative evaluations such as KT-2000 or Biodex.

  View details for DOI 10.1007/s00167-006-0198-3

  View details for Web of Science ID 000245431300004

  View details for PubMedID 16972109

• Clinical disability in posterior cruciate ligament deficient patients does not relate to knee laxity, but relates to dynamic knee function during stair descending KNEE SURGERY SPORTS TRAUMATOLOGY ARTHROSCOPY Iwata, S., Suda, Y., Nagura, T., Matsumoto, H., Otani, T., Andriacchi, T. P., Toyama, Y. 2007; 15 (3): 258-265

  Abstract

  We investigated the factors which influence clinical subjective symptoms during activities in PCL deficient patients by evaluating knee laxity, muscle strength and knee mechanics during level walking, stair ascent and descent. Twenty-two subjects with isolated PCL deficient knees and 20 healthy volunteers were involved. The PCL deficient patients were divided into two subgroups based on previous history of experiencing giving-way during stair descent; a giving-way group (10 subjects) and a non giving-way group (12 subjects). Giving-way during activities of daily living is a key symptom in isolated PCL deficient patients. No statistically significant differences in the knee laxity, muscle strength and knee mechanics during level walking and were observed between the giving-way group and the non giving-way group. However, we found significant differences in the knee mechanics during stair ascent and descent between the two groups, and these differences were more remarkable during stair descent. Peak values of knee flexion angle, external knee flexion moment and posterior knee force during early stance phase were significantly lower in the giving-way group than in the non giving-way group. This study indicated that the symptom of giving-way during stair descent was related to knee mechanics during stair descent, unlike other quantitative evaluations such as KT-2000 or Biodex.

  View details for DOI 10.1007/s00167-006-0183-x

  View details for Web of Science ID 000245842200008

  View details for PubMedID 16967199

• A comparison of the influence of global functional loads vs. local contact anatomy on articular cartilage thickness at the knee JOURNAL OF BIOMECHANICS Koo, S., Andriacchi, T. P. 2007; 40 (13): 2961-2966

  Abstract

  Cartilage contact geometry, along with joint loading, can play an important role in determining local articular cartilage tissue stress. Thus individual variations in cartilage thickness can be associated with both individual variations in joint loading associated with activities of daily living as well as individual differences in the anatomy of the contacting surfaces of the joint. The purpose of this study was to isolate the relationship between cartilage thickness predicted by individual variations in contact surface geometry based on the radii of the femur and tibia vs. cartilage thickness predicted by individual variations in joint loading. Knee magnetic resonance (MR) images and the peak knee adduction moments during walking were obtained from 11 young healthy male subjects (age 30.5+/-5.1 years). The cartilage thicknesses and surface radii of the femoral and tibial cartilage were measured in the weight-bearing regions of the medial and lateral compartments of three-dimensional models from the MR images. The ratio of contact pressure between the medial and lateral compartments was calculated from the radii of tibiofemoral contact surface geometries. The results showed that the medial to lateral pressure ratios were not correlated with the medial to lateral cartilage thickness ratios. However, in general, pressure was higher in the lateral than medial compartments and cartilage was thicker in the lateral than medial compartments. The peak knee adduction moment showed a significant positive linear correlation with medial to lateral thickness ratio in both femur (R(2)=0.43,P<0.01) and tibia (R(2)=0.32,P<0.01). The results of this study suggest that the dynamics of walking is an important factor to describe individual differences in cartilage thickness for normal subjects.

  View details for DOI 10.1016/j.jbiomech.2007.02.005

  View details for Web of Science ID 000250277800017

  View details for PubMedID 17418219

  View details for PubMedCentralID PMC2358971

• Numerical and experimental analysis of articular chondrocyte deformation: Calibration of a multiscale finite element model ASME Summer Bioengineering Conference Bevill, S. L., Briant, P. L., Andriacchi, T. P. AMER SOC MECHANICAL ENGINEERS. 2007: 321–322

  View details for Web of Science ID 000252105700161

• Quantifying variations in collagen matrix deformation in loaded articular cartilage ASME Summer Bioengineering Conference Briant, P., Bevill, S., Andriacchi, T. P. AMER SOC MECHANICAL ENGINEERS. 2007: 931–932

  View details for Web of Science ID 000252105700466

• Accurately measuring human movement using articulated ICP with soft-joint constraints and a repository of articulated models IEEE Conference on Computer Vision and Pattern Recognition Mundermann, L., Corazza, S., Andriacchi, T. P. IEEE. 2007: 2550–2555

  View details for Web of Science ID 000250382805019

• The influence of deceleration forces on ACL strain during single-leg landing: A simulation study JOURNAL OF BIOMECHANICS Shin, C. S., Chaudhari, A. M., Andriacchi, T. P. 2007; 40 (5): 1145-1152

  Abstract

  Anterior cruciate ligament (ACL) injury commonly occurs during single limb landing or stopping from a run, yet the conditions that influence ACL strain are not well understood. The purpose of this study was to develop, test and apply a 3D specimen-specific dynamic simulation model of the knee designed to evaluate the influence of deceleration forces during running to a stop (single-leg landing) on ACL strain. This work tested the conceptual development of the model by simulating a physical experiment that provided direct measurements of ACL strain during vertical impact loading (peak value 1294N) with the leg near full extension. The properties of the soft tissue structures were estimated by simulating previous experiments described in the literature. A key element of the model was obtaining precise anatomy from segmented MR images of the soft tissue structures and articular geometry for the tibiofemoral and patellofemoral joints of the knee used in the cadaver experiment. The model predictions were correlated (Pearson correlation coefficient 0.889) to the temporal and amplitude characteristic of the experimental strains. The simulation model was then used to test the balance between ACL strain produced by quadriceps contraction and the reductions in ACL strain associated with the posterior braking force. When posterior forces that replicated in vivo conditions were applied, the peak ACL strain was reduced. These results suggest that the typical deceleration force that occurs during running to a single limb landing can substantially reduce the strain in the ACL relative to conditions associated with an isolated single limb landing from a vertical jump.

  View details for DOI 10.1016/j.jbiomech.2006.05.004

  View details for Web of Science ID 000245565400022

  View details for PubMedID 16797556

• A framework for the functional identification of joint centers using markerless motion capture, validation for the hip joint JOURNAL OF BIOMECHANICS Corazza, S., Muendermann, L., Andriacchi, T. 2007; 40 (15): 3510-3515

  Abstract

  The objective of the study was to develop a framework for the accurate identification of joint centers to be used for the calculation of human body kinematics and kinetics. The present work introduces a method for the functional identification of joint centers using markerless motion capture (MMC). The MMC system used 8 color VGA cameras. An automatic segmentation-registration algorithm was developed to identify the optimal joint center in a least-square sense. The method was applied to the hip joint center with a validation study conducted in a virtual environment. The results had an accuracy (6mm mean absolute error) below the current MMC system resolution (1cm voxel resolution). Direct experimental comparison with marker-based methods was carried out showing mean absolute deviations over the three anatomical directions of 11.9 and 15.3mm if compared with either a full leg or only thigh markers protocol, respectively. Those experimental results were presented only in terms of deviations between the two systems (marker-based and markerless) as no real gold standard was available. The methods presented in this paper provide an important enabling step towards the biomechanical and clinical applications of markerless motion capture.

  View details for DOI 10.1016/j.jbiomech.2007.05.029

  View details for Web of Science ID 000251342800026

  View details for PubMedID 17697684

• Tibiofemoral joint contact force in deep knee flexion and its consideration in knee osteoarthritis and joint replacement JOURNAL OF APPLIED BIOMECHANICS Nagura, T., Matsumoto, H., Kiriyama, Y., Chaudhari, A., Andriacchi, T. P. 2006; 22 (4): 305-313

  Abstract

  The aim of the study was to estimate the tibiofemoral joint force in deep flexion to consider how the mechanical load affects the knee. We hypothesize that the joint force should not become sufficiently large to damage the joint under normal contact area, but should become deleterious to the joint under the limited contact area. Sixteen healthy knees were analyzed using a motion capture system, a force plate, a surface electromyography, and a knee model, and then tibiofemoral joint contact forces were calculated. Also, a contact stress simulation using the contact areas from the literature was performed. The peak joint contact forces (M +/- SD) were 4566 +/- 1932 N at 140 degrees in rising from full squat and 4479 +/- 1478 N at 90 degrees in rising from kneeling. Under normal contact area, the tibiofemoral contact stresses in deep flexion were less than 5 MPa and did not exceed the stress to damage the cartilage. The contact stress simulation suggests that knee prosthesis having the contact area smaller than 200 mm2 may be problematic since the contact stress in deep flexion would become larger than 21 MPa, and it would lead damage or wear of the polyethylene.

  View details for Web of Science ID 000242264900007

  View details for PubMedID 17293627

• The role of ambulatory mechanics in the initiation and progression of knee osteoarthritis CURRENT OPINION IN RHEUMATOLOGY Andriacchi, T. P., Muendermann, A. 2006; 18 (5): 514-518

  Abstract

  This review examines recent in-vivo studies of ambulation and discusses the fundamental role of mechanics of ambulation in the initiation and progression of osteoarthritis at the knee.Recent studies have supported earlier findings that a high adduction moment at the knee during ambulation was most frequently reported to influence the progression of medial compartment osteoarthritis. In contrast to previous findings in patients with osteoarthritis, recent work on healthy subjects reports that cartilage thickness increases with high ambulatory loads. Kinematic changes were associated with the initiation of osteoarthritis. Recent studies of subjects with high risk factors for knee osteoarthritis (obesity and anterior cruciate ligament injury) reported a relationship between kinematic changes during ambulation and the initiation of osteoarthritis at the knee. This review also contrasts the relative influence on osteoarthritis of knee mechanics measured during ambulatory and nonambulatory activities.The initiation of osteoarthritis occurs when healthy cartilage experiences some condition (traumatic or chronic) that causes kinematic changes during ambulation at the knee to shift the load-bearing contact location of the joint to a region not conditioned to the new loading. The rate of progression of osteoarthritis is associated with increased load during ambulation.

  View details for Web of Science ID 000240652900014

  View details for PubMedID 16896293

• A markerless motion capture system to study musculoskeletal biomechanics: Visual hull and simulated annealing approach ANNALS OF BIOMEDICAL ENGINEERING Corazza, S., Mundermann, L., Chaudhari, A. M., Demattio, T., Cobelli, C., Andriacchi, T. P. 2006; 34 (6): 1019-1029

  Abstract

  Human motion capture is frequently used to study musculoskeletal biomechanics and clinical problems, as well as to provide realistic animation for the entertainment industry. The most popular technique for human motion capture uses markers placed on the skin, despite some important drawbacks including the impediment to the motion by the presence of skin markers and relative movement between the skin where the markers are placed and the underlying bone. The latter makes it difficult to estimate the motion of the underlying bone, which is the variable of interest for biomechanical and clinical applications. A model-based markerless motion capture system is presented in this study, which does not require the placement of any markers on the subject's body. The described method is based on visual hull reconstruction and an a priori model of the subject. A custom version of adapted fast simulated annealing has been developed to match the model to the visual hull. The tracking capability and a quantitative validation of the method were evaluated in a virtual environment for a complete gait cycle. The obtained mean errors, for an entire gait cycle, for knee and hip flexion are respectively 1.5 degrees (+/-3.9 degrees ) and 2.0 degrees (+/-3.0 degrees ), while for knee and hip adduction they are respectively 2.0 degrees (+/-2.3 degrees ) and 1.1 degrees (+/-1.7 degrees ). Results for the ankle and shoulder joints are also presented. Experimental results captured in a gait laboratory with a real subject are also shown to demonstrate the effectiveness and potential of the presented method in a clinical environment.

  View details for DOI 10.1007/s10439-006-9122-8

  View details for Web of Science ID 000238546800012

  View details for PubMedID 16783657

• Comparison of quantitative cartilage measurements acquired on two 3.0T MRI systems from different manufacturers JOURNAL OF MAGNETIC RESONANCE IMAGING Kornaat, P. R., Koo, S., Andriacchi, T. P., Bloem, J. L., Gold, G. E. 2006; 23 (5): 770-773

  Abstract

  To investigate the comparability of two osteoarthritis (OA) surrogate endpoints--average cartilage thickness and cartilage volume--acquired from healthy volunteers on two 3.0T magnetic resonance imaging (MRI) systems from different manufacturers.Ten knees of five healthy volunteers were scanned on a 3.0T General Electric (GE) and a 3.0T Philips scanner using a fast three-dimensional fat-suppressed spoiled gradient (SPGR) imaging sequence. The acquisition parameters were optimized beforehand and were kept as comparable as possible on both scanners. For quantitative analysis, the average cartilage thickness and volume of the load-bearing regions of the femoral condyles were compared. Data were analyzed using a univariate repeated-measures analysis of variance (ANOVA) to examine the effects of position, condyle, and imaging system on the measurements.The average cartilage thickness and volume of the load-bearing regions of the femoral condyles did not differ between the two different 3.0T MRI systems (P > 0.05). There was no significant effect of position or condyle on the average cartilage thickness measurements (P > 0.05; range = 0.41-0.93) or cartilage volume (P > 0.05; range = 0.14-0.87).Two OA surrogate endpoints--average cartilage thickness and cartilage volume--acquired on two 3.0T MRI systems from different manufacturers are comparable.

  View details for DOI 10.1002/jmri.20561

  View details for Web of Science ID 000237124800023

  View details for PubMedID 16568430

• The evolution of methods for the capture of human movement leading to markerless motion capture for biomechanical applications JOURNAL OF NEUROENGINEERING AND REHABILITATION Mundermann, L., Corazza, S., Andriacchi, T. P. 2006; 3

  Abstract

  Over the centuries the evolution of methods for the capture of human movement has been motivated by the need for new information on the characteristics of normal and pathological human movement. This study was motivated in part by the need of new clinical approaches for the treatment and prevention of diseases that are influenced by subtle changes in the patterns movement. These clinical approaches require new methods to measure accurately patterns of locomotion without the risk of artificial stimulus producing unwanted artifacts that could mask the natural patterns of motion. Most common methods for accurate capture of three-dimensional human movement require a laboratory environment and the attachment of markers or fixtures to the body's segments. These laboratory conditions can cause unknown experimental artifacts. Thus, our understanding of normal and pathological human movement would be enhanced by a method that allows the capture of human movement without the constraint of markers or fixtures placed on the body. In this paper, the need for markerless human motion capture methods is discussed and the advancement of markerless approaches is considered in view of accurate capture of three-dimensional human movement for biomechanical applications. The role of choosing appropriate technical equipment and algorithms for accurate markerless motion capture is critical. The implementation of this new methodology offers the promise for simple, time-efficient, and potentially more meaningful assessments of human movement in research and clinical practice. The feasibility of accurately and precisely measuring 3D human body kinematics for the lower limbs using a markerless motion capture system on the basis of visual hulls is demonstrated.

  View details for DOI 10.1186/1743-0003-3-6

  View details for Web of Science ID 000251218700001

  View details for PubMedID 16539701

  View details for PubMedCentralID PMC1513229

• Comment: effect of fatigue on knee kinetics and kinematics in stop-jump tasks. American journal of sports medicine Chaudhari, A. M., Andriacchi, T. P. 2006; 34 (2): 312-?

  View details for PubMedID 16423915

• The mechanical consequences of dynamic frontal plane limb alignment for non-contact ACL injury JOURNAL OF BIOMECHANICS Chaudhari, A. M., Andriacchi, T. P. 2006; 39 (2): 330-338

  Abstract

  This study investigated the mechanical consequences of differences in dynamic frontal plane alignment of the support limb and the influence of anticipatory muscle activation at the hip and ankle on reducing the potential for non-contact ACL injury during single-limb landing. A frontal plane, three-link passive dynamic model was used to estimate an ACL non-contact injury threshold. This threshold was defined as the maximum axial force that the knee could sustain before the joint opened 8 degrees either medially or laterally, which was deemed sufficient to cause injury. The limb alignment and hip and ankle muscle contractions were varied to determine their effects on the ACL injury threshold. Valgus or varus alignment reduced the injury threshold compared to neutral alignment, but increasing the anticipatory contraction of hip abduction and adduction muscle groups increased the injury threshold. Increasing anticipatory ankle inversion/eversion muscle contraction had no effect. This study provides a mechanical rationale for the conclusion that a neutral limb alignment (compared to valgus or varus) during landing and increasing hip muscle contraction (abductors/adductors) prior to landing can reduce the possibility of ACL rupture through a valgus or varus opening mechanism.

  View details for DOI 10.1016/j.jbiomech.2004.11.013

  View details for Web of Science ID 000234117900014

  View details for PubMedID 16321635

• Measuring human movement for biomechanical applications using markerless motion capture Conference on Three-Dimensional Image Capture and Application VII Mundermann, L., Corazza, S., Chaudhari, A. M., Andriacchi, T. P., Sundaresan, A., Chellappa, R. SPIE-INT SOC OPTICAL ENGINEERING. 2006

  View details for Web of Science ID 000237082900025

• Rotational changes at the knee after ACL injury cause cartilage thinning CLINICAL ORTHOPAEDICS AND RELATED RESEARCH Andriacchi, T. P., Briant, P. L., Bevill, S. L., Koo, S. 2006: 39-44

  Abstract

  We examined the relationship between specific gait changes after anterior cruciate ligament injury and the progression of osteoarthritis at the knee. The study was done using a finite-element model derived from subject specific three-dimensional cartilage volumes created from magnetic resonance images. Cartilage thinning was predicted using an iterative algorithm based on the octahedral shear stress. Simulations were done for a knee with normal alignment and for a knee with an internal tibial rotation offset, as associated with anterior cruciate ligament deficiency. For the healthy knee, the model predicted patterns of cartilage thinning consistent with a previous clinical report of idiopathic osteoarthritis. For the ACL-deficient scenario the model predicted a more rapid rate of cartilage thinning throughout the knee, especially in the medial compartment. The results suggest that the progression of osteoarthritis after anterior cruciate ligament injury is associated with a shift in the normal load bearing regions of the knee joint during normal function due to kinematic changes, and highlight the importance of restoring proper gait during anterior cruciate ligament reconstruction.

  View details for DOI 10.1097/01.blo.0000197079.26600.09

  View details for Web of Science ID 000243019700008

  View details for PubMedID 16394737

• Considerations in measuring cartilage thickness using MRI: factors influencing reproducibility and accuracy OSTEOARTHRITIS AND CARTILAGE Koo, S., Gold, G. E., Andriacchi, T. P. 2005; 13 (9): 782-789

  Abstract

  The primary goal of this study was to describe and evaluate conditions that could influence the precision and accuracy of measuring in vivo cartilage thickness in the weight bearing regions of the knee from magnetic resonance imaging (MRI).Three-dimensional (3D) models of the femoral cartilage were created from segmented MR images. The weight bearing regions on femoral cartilage were selected for the portion of the tibiofemoral joint that sustains contact during walking. Six regions of interest (three on each condyle) were located on the femur. Average cartilage thickness was calculated over each region. The sensitivity of the precision of the measurements to observer variability was evaluated using intra- and inter-observer reproducibility tests of cartilage thickness measurements from the MRI-derived 3D models. In addition, the quantitative influence of a rule-based protocol for segmentation was evaluated using the inter-observer reproducibility protocol. Accuracy tests were conducted on porcine knees by comparing 3D models from MR images and laser scans across weight bearing and non-weight bearing regions.The precision was substantially better for the intra-observer tests (Coefficient of variation (CV) = 1-3%) than the inter-observer tests. Adding a rule-based protocol reduced variability in inter-observer tests substantially (CV = 6.6% vs 8.3%). Accuracy tests showed that the central and weight bearing regions on each condyle were more accurate than boundary and non-weight bearing regions. In addition, these results indicate that care should be taken when determining cartilage thickness of weight bearing regions with cartilage degenerations, since the thickness of thinner cartilage can be systematically overestimated in MR images.A rule-based approach can substantially increase inter-observer reproducibility when measuring cartilage thickness from multiple observers. This improvement in inter-observer reproducibility could be an important consideration for longitudinal studies of disease progression. In quantifying cartilage thickness, central and weight bearing regions on each condyle can provide more accurate measurement than boundary and non-weight bearing regions with average accuracy of +/-0.2-0.3 mm. An important finding of this study was that the weight bearing regions, which are usually of the greatest clinical interest, were measured most accurately by sagittal plane imaging.

  View details for DOI 10.1016/j.joca.2005.04.013

  View details for Web of Science ID 000232252100005

  View details for PubMedID 15961328

• Secondary gait changes in patients with medial compartment knee osteoarthritis - Increased load at the ankle, knee, and hip during walking ARTHRITIS AND RHEUMATISM Mundermann, A., Dyrby, C. O., Andriacchi, T. P. 2005; 52 (9): 2835-2844

  Abstract

  This study tested the hypothesis that gait changes related to knee osteoarthritis (OA) of varied severity are associated with increased loads at the ankle, knee, and hip.Forty-two patients with bilateral medial compartment knee OA and 42 control subjects matched for sex, age, height, and mass were studied. Nineteen patients had Kellgren/Lawrence (K/L) radiographic severity grades of 1 or 2, and 23 patients had K/L grades of 3 or 4. Three-dimensional kinematics and kinetics were measured in the hip, knee, and ankle while the subjects walked at a self-selected speed.Patients with more severe knee OA had greater first peak knee adduction moments than their matched control subjects (P = 0.039) and than patients with less severe knee OA (P < 0.001). All patients with knee OA made initial contact with the ground with the knee in a more extended position than that exhibited by control subjects. An increased axial loading rate was present in all joints of the lower extremity. Patients with more severe knee OA had lower hip adduction moments compared with their matched control subjects.The secondary gait changes observed among patients with knee OA reflect a potential strategy to shift the body's weight more rapidly from the contralateral limb to the support limb, which appears to be successful in reducing the load at the knee in only patients with less severe knee OA. The increased loading rate in the lower extremity joints may lead to a faster progression of existing OA and to the onset of OA at joints adjacent to the knee. Interventions for knee OA should therefore be assessed for their effects on the mechanics of all joints of the lower extremity.

  View details for DOI 10.1002/art.21262

  View details for Web of Science ID 000232115700031

  View details for PubMedID 16145666

• The influence of slip velocity on wear of total knee arthroplasty WEAR Schwenke, T., Borgstede, L. L., Schneider, E., Andriacchi, T. P., Wimmer, M. A. 2005; 259: 926-932

  View details for DOI 10.1016/j.wear.2005.01.049

  View details for Web of Science ID 000230370300017

• Sport-dependent variations in arm position during single-limb landing influence knee loading - Implications for anterior cruciate ligament injury AMERICAN JOURNAL OF SPORTS MEDICINE Chaudhari, A. M., Hearn, B. K., Andriacchi, T. P. 2005; 33 (6): 824-830

  Abstract

  Increased valgus loading at the knee has been previously identified as a possible risk factor for noncontact anterior cruciate ligament injuries, which are common in sports. Arm position variation may affect risk of injury by altering valgus knee loading.Sport-dependent variations in arm position increase valgus loading of the knee during run-to-cut maneuvers.Controlled laboratory study.Eleven subjects performed a sidestep cutting maneuver, first with no arm constraints and then with 3 sports-related arm positions in random order (holding a lacrosse stick, holding a football on the plant side, and holding a football on the cut side). The analysis focused on the knee valgus moment relative to the arm positions during the landing phase of the activity.Arm position significantly influenced the valgus moment with an increase in the lacrosse trials and in the plant-side football trials but not in the cut-side football trials (alpha = .05).Constraining the plant-side arm results in increased valgus loading at the knee during run-to-cut maneuvers, which suggests the possibility of greater risk of anterior cruciate ligament injury during these conditions.These results suggest that training methods that consider arm position as a risk factor could help reduce the risk of anterior cruciate ligament noncontact injury.

  View details for DOI 10.1177/0363546504270455

  View details for Web of Science ID 000229314300004

  View details for PubMedID 15827366

• MR imaging of articular cartilage at 1.5T and 3.0T: Comparison of SPGR and SSFP sequences 9th World Congress of the OsteoArthritis-Research-Society-International Kornaat, P. R., Reeder, S. B., Koo, S., Brittain, J. H., Yu, H., Andriacchi, T. P., Gold, G. E. ELSEVIER SCI LTD. 2005: 338–44

  Abstract

  To compare articular cartilage signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and thickness measurements on a 1.5 T and a 3.0 T magnetic resonance (MR) scanner using three-dimensional spoiled gradient recalled echo (3D-SPGR) and two 3D steady-state free precession (SSFP) sequences.Both knees of five volunteers were scanned at 1.5 T and at 3.0 T using a transmit-receive quadrature extremity coil. Each examination consisted of a sagittal 3D-SPGR sequence, a sagittal fat suppressed 3D-SSFP (FS-SSFP) sequence, and a sagittal Dixon 3D-SSFP sequence. For quantitative analysis, we compared cartilage SNR and CNR efficiencies, as well as average cartilage thickness measurements.For 3D-SPGR, cartilage SNR efficiencies at 3.0 T increased compared to those at 1.5 T by a factor of 1.83 (range: 1.40-2.09). In comparison to 3D-SPGR, the SNR efficiency of FS-SSFP increased by a factor of 2.13 (range: 1.81-2.39) and for Dixon SSFP by a factor of 2.39 (range: 1.95-2.99). For 3D-SPGR, CNR efficiencies between cartilage and its surrounding tissue increased compared to those at 1.5 T by a factor of 2.12 (range: 1.75-2.47), for FS-SSFP by a factor 2.11 (range: 1.58-2.80) and for Dixon SSFP by a factor 2.39 (range 2.09-2.83). Average cartilage thicknesses of load bearing regions were not different at both field strengths or between sequences (P>0.05). Mean average cartilage thickness measured in all knees was 2.28 mm.Articular cartilage imaging of the knee on a 3.0 T MR scanner shows increased SNR and CNR efficiencies compared to a 1.5 T scanner, where SSFP-based techniques show the highest increase in SNR and CNR efficiency. There was no difference between average cartilage thickness measurements performed at the 1.5 T and 3.0 T scanners or between the three different sequences.

  View details for DOI 10.1016/j.joca.2004.12.008

  View details for Web of Science ID 000228216200008

  View details for PubMedID 15780647

• Interactions between kinematics and loading during walking for the normal and ACL deficient knee JOURNAL OF BIOMECHANICS Andriacchi, T. P., Dyrby, C. O. 2005; 38 (2): 293-298

  Abstract

  The relationships between extrinsic forces acting at the knee and knee kinematics were examined with the purpose of identifying specific phases of the walking cycle that could cause abnormal kinematics in the anterior cruciate ligament (ACL) deficient knee. Intersegmental forces and moments in directions that would produce anterior-posterior (AP) translation, internal-external (IE) rotation and flexion-extension (FE) at the knee were compared with the respective translation and rotations of the tibia relative to the femur during four selected phases (heel strike, weight acceptance, terminal extension and swing) of the walking cycle. The kinematic changes associated with loss of the ACL occurred primarily during the terminal portion of swing phase of the walking cycle where, for the ACL deficient knee, the tibia had reduced external rotation and anterior translation as the knee extended prior to heel strike. The kinematic changes during swing phase were associated with a rotational offset relative to the contralateral knee in the average position of the tibia towards internal rotation. The offset was maintained through the entire gait cycle. The abnormal offsets in the rotational position were correlated with the magnitude of the flexion moment (balanced by a net quadriceps moment) during weight acceptance. These results suggest that adaptations to the patterns of muscle firing during walking can compensate for kinematic changes associated with the loss of the ACL. The altered rotational position would cause changes in tibiofemoral contact during walking that could cause the type of degenerative changes reported in the meniscus and the articular cartilage following ACL injury.

  View details for DOI 10.1016/j.jbiomech.2004.02.010

  View details for Web of Science ID 000226463100012

  View details for PubMedID 15598456

• Serum concentration of cartilage oligomeric matrix protein (COMP) is sensitive to physiological cyclic loading in healthy adults OSTEOARTHRITIS AND CARTILAGE Mundermann, A., Dyrby, C. O., Andriacchi, T. P., King, K. B. 2005; 13 (1): 34-38

  Abstract

  To test the hypothesis that physiological cyclic loading during a 30-min walking exercise causes an increase in serum cartilage oligomeric matrix protein (COMP) concentration in a healthy population.Blood samples (5 ml) were drawn from 10 physically active adults immediately before and after, and 0.5h, 1.5h, 3.5h and 5.5h after a 30-min walking exercise on a level outdoor walking track at self-selected normal speed. On a separate day, blood samples were drawn from the same 10 subjects during 6h while they were resting in a chair. Serum COMP concentrations were determined using a commercial enzyme-linked immunosorbent assay (COMP ELISA). An activity monitor was used to record basic time-distance measurements of gait. Serum COMP concentrations within the exercise protocol and within the resting protocol were compared using separate repeated measures analyses of variance (alpha=0.05).In the exercise protocol, a first increase (9.7%; P=0.003) occurred immediately after the walking exercise. A second increase in serum COMP concentration (7.0%; P=0.024) occurred 5.5h after the walking exercise. In the resting protocol, the concentration at baseline was significantly higher than at all subsequent time points (8.2%; P<0.050). Serum COMP concentration decreased from the 3.5-h to the 5.5-h sample (-4.8%; P=0.012).Even a moderate walking activity can significantly influence serum COMP concentration. The immediate response points to a diffusion time of COMP fragments from cartilage to the blood of 30 min or less. The response at 5.5h indicates a metabolic delay for COMP in the range of 5h to 6h.

  View details for DOI 10.1016/j.joca.2004.09.007

  View details for Web of Science ID 000226546700005

  View details for PubMedID 15639635

• Most favorable camera configuration for a shape-from-silhouette markerless motion capture system for biomechanical analysis Conference Videometrics VIII Mundermann, L., Corazza, S., Chaudhari, A. M., Alexander, E. J., Andriacchi, T. P. SPIE-INT SOC OPTICAL ENGINEERING. 2005: 278–287

  View details for Web of Science ID 000228789200029

• Conditions that influence the accuracy of anthropometric parameter estimation for human body segments using shape-from-silhouette Conference Videometrics VIII Mundermann, L., Mundermann, A., Chaudhari, A. M., Andriacchi, T. P. SPIE-INT SOC OPTICAL ENGINEERING. 2005: 268–277

  View details for Web of Science ID 000228789200028

• The mechanobiology of articular cartilage development and degeneration Carl T Brighton Annual Workshop Carter, D. R., Beaupre, G. S., Wong, M., Smith, R. L., Andriacchi, T. P., Schurman, D. J. SPRINGER. 2004: S69–S77

  Abstract

  The development, maintenance, and destruction of cartilage are regulated by mechanical factors throughout life. Mechanical cues in the cartilage fetal endoskeleton influence the expression of genes that guide the processes of growth, vascular invasion, and ossification. Intermittent fluid pressure maintains the cartilage phenotype whereas mild tension (or shear) promotes growth and ossification. The articular cartilage thickness is determined by the position at which the subchondral growth front stabilizes. In mature joints, cartilage is thickest and healthiest where the contact pressure and cartilage fluid pressure are greatest. The depth-dependent histomorphology reflects the local fluid pressure, tensile strain, and fluid exudation. Osteoarthritis represents the final demise and loss of cartilage in the skeletal elements. The initiation and progression of osteoarthritis can follow many pathways and can be promoted by mechanical factors including: (1) reduced loading, which activates the subchondral growth front by reducing fluid pressure; (2) blunt impact, causing microdamage and activation of the subchondral growth front by local shear stress; (3) mechanical abnormalities that increase wear at the articulating surface; and (4) other mechanically related factors. Research should be directed at integrating our mechanical understanding of osteoarthritis pathogenesis and progression within the framework of cellular and molecular events throughout ontogeny.

  View details for DOI 10.1097/01.blo.0000144970.05107.7e

  View details for Web of Science ID 000224524400014

  View details for PubMedID 15480079

• Secondary motions of the knee during weight bearing and non-weight bearing activities JOURNAL OF ORTHOPAEDIC RESEARCH Dyrby, C. O., Andriacchi, T. P. 2004; 22 (4): 794-800

  Abstract

  The objective of this study was to test the hypothesis that during a weight bearing activity such as walking, a dynamic range (envelope of motion) exists in the relationship between the secondary knee motions (anterior-posterior (AP) translation, internal-external (IE) rotation, and abduction-adduction (Ab-Adduction)) and knee flexion angle. In addition differences in the envelope of motion between a weight bearing and non-weight bearing activity were tested. The hypothesis was evaluated by testing for differences (offsets) in secondary displacements at specific knee flexion angles during the walking cycle and seated leg extension (non-weight bearing). Kinematic measurements were obtained using a previously developed point cluster technique to analyze the six-degrees of freedom movement of the knee. During walking, phase plots of the IE rotation and AP translation versus knee flexion demonstrated significant offsets from one phase of the gait cycle to another at the same flexion angle. During the non-weight bearing activity, no significant offset in the secondary movement was found; the knee followed the same pathway of motion during the flexion and extension phase of this activity. The characteristics of the secondary motions during walking indicated that secondary knee movements are caused by the external forces (muscle, inertial and gravitational) that act on the knee during the various phases of the walking cycle. The boundaries of the envelope appear to reflect the characteristics of the passive restraints. The weight bearing secondary motion AP and IE rotation seen during a walking activity demonstrated an envelope of dynamic laxity that could potentially be used to evaluate functional instabilities at the knee.

  View details for DOI 10.1016/j.orthres.2003.11.003

  View details for Web of Science ID 000222402000015

  View details for PubMedID 15183436

• Functional evaluation of the Scandinavian Total Ankle Replacement FOOT & ANKLE INTERNATIONAL Dyrby, C., Chou, L. B., Andriacchi, T. P., Mann, R. A. 2004; 25 (6): 377-381

  Abstract

  The purpose of this study was to evaluate the function of the ankle joint during walking before and after Scandinavian Total Ankle Replacement (STAR). Nine patients (six males and three females) with an average age of 65 years, scheduled for unilateral total ankle replacement for osteoarthritis and rheumatoid arthritis, were evaluated both preoperatively and postoperatively in a gait analysis laboratory. Arthroplasty patients showed reduced range of motion at the ankle compared to normal controls. Postoperative arthroplasty subjects had significantly improved external ankle dorsiflexion moment, the moment that affects the plantarflexor muscles, when compared to their preoperative status. The moment in arthroplasty patients was increased, indicating improved function of the ankle joint.

  View details for PubMedID 15215020

• Potential strategies to reduce medial compartment loading in patients with knee osteoarthritis of varying severity - Reduced walking speed ARTHRITIS AND RHEUMATISM Mundermann, A., Dyrby, C. O., Hurwitz, D. E., Sharma, L., Andriacchi, T. P. 2004; 50 (4): 1172-1178

  Abstract

  To determine whether reducing walking speed is a strategy used by patients with knee osteoarthritis (OA) of varying disease severity to reduce the maximum knee adduction moment.Self-selected walking speeds and maximum knee adduction moments of 44 patients with medial tibiofemoral OA of varying disease severity, as assessed by using the Kellgren/Lawrence grade, were compared with those of 44 asymptomatic control subjects matched for sex, age, height, and weight.Differences in self-selected normal walking speed explained only 8.9% of the variation in maximum knee adduction moment for the group of patients with knee OA. The severity of the disease influenced the adduction moment-walking speed relationship; the individual slopes of this relationship were significantly greater in patients with less severe OA than in asymptomatic matched control subjects. Self-selected walking speed did not differ between patients with knee OA, regardless of the severity, and asymptomatic control subjects. However, knees with more-severe OA had significantly greater adduction moments (mean +/- SD 3.80 +/- 0.89% body weight x height) and were in more varus alignment (6.0 +/- 4.5 degrees ) than knees with less-severe OA (2.94 +/- 0.70% body weight x height; and 0.0 +/- 2.9 degrees, respectively).Patients with less-severe OA adapt a walking style that differs from that of patients with more-severe OA and controls. This walking style is associated with the potential to reduce the adduction moment when walking at slower speeds and could be linked to decreased disease severity.

  View details for DOI 10.1002/art.20132

  View details for Web of Science ID 000220763600018

  View details for PubMedID 15077299

• Sensitivity of finite helical axis parameters to temporally varying realistic motion utilizing an idealized knee model PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART H-JOURNAL OF ENGINEERING IN MEDICINE Johnson, T. S., Andriacchi, T. P., Erdman, A. G. 2004; 218 (H2): 89-100

  Abstract

  Various uses of the screw or helical axis have previously been reported in the literature in an attempt to quantify the complex displacements and coupled rotations of in vivo human knee kinematics. Multiple methods have been used by previous authors to calculate the axis parameters, and it has been theorized that the mathematical stability and accuracy of the finite helical axis (FHA) is highly dependent on experimental variability and rotation increment spacing between axis calculations. Previous research has not addressed the sensitivity of the FHA for true in vivo data collection, as required for gait laboratory analysis. This research presents a controlled series of experiments simulating continuous data collection as utilized in gait analysis to investigate the sensitivity of the three-dimensional finite screw axis parameters of rotation, displacement, orientation and location with regard to time step increment spacing, utilizing two different methods for spatial location. Six-degree-of-freedom motion parameters are measured for an idealized rigid body knee model that is constrained to a planar motion profile for the purposes of error analysis. The kinematic data are collected using a multicamera optoelectronic system combined with an error minimization algorithm known as the point cluster method. Rotation about the screw axis is seen to be repeatable, accurate and time step increment insensitive. Displacement along the axis is highly dependent on time step increment sizing, with smaller rotation angles between calculations producing more accuracy. Orientation of the axis in space is accurate with only a slight filtering effect noticed during motion reversal. Locating the screw axis by a projected point onto the screw axis from the mid-point of the finite displacement is found to be less sensitive to motion reversal than finding the intersection of the axis with a reference plane. A filtering effect of the spatial location parameters was noted for larger time step increments during periods of little or no rotation.

  View details for Web of Science ID 000221365400001

• Non-rigid modeling of body segments for improved skeletal motion estimation CMES-COMPUTER MODELING IN ENGINEERING & SCIENCES Alexander, E. J., Bregler, C., Andriacchi, T. P. 2003; 4 (3-4): 351-364

  View details for Web of Science ID 000184485100002

• Self-reported giving-way episode during a stepping-down task: Case report of a subject with an ACL-deficient knee - Invited commentary JOURNAL OF ORTHOPAEDIC & SPORTS PHYSICAL THERAPY Andriacchi, T., Chaudhari, A. 2003; 33 (5): 283-284

  View details for Web of Science ID 000184217100007

• The use of functional analysis in evaluating knee kinematics CLINICAL ORTHOPAEDICS AND RELATED RESEARCH Andriacchi, T. P., Dyrby, C. O., Johnson, T. S. 2003: 44-53

  Abstract

  The importance of understanding the six-degrees-of-freedom kinematics of the knee during ambulatory activities was examined in the context of the function of total knee arthroplasty. Studies of knee kinematics during walking, stair climbing, and a deep flexion squat indicate that knee kinematics is activity-dependent. A comparative study of patients and healthy subjects during stair climbing indicates the importance of maintaining the function of the posterior cruciate ligament. A second study used walking kinematics derived from patient testing as input to a wear simulator. There was increased wear relative to standard simulator input that was related to the slip velocity at the contact surface. Finally, results from a study of deep flexion indicate that substantial femoral rotation is required during deep flexion activities. The current study shows the importance of studying in vivo knee kinematics for future enhancement in the treatment of the arthritic knee.

  View details for DOI 10.1097/01.blo.0000062383.79828.f5

  View details for Web of Science ID 000182630400007

  View details for PubMedID 12771816

• A new parametric approach for modeling hip forces during gait JOURNAL OF BIOMECHANICS Hurwitz, D. E., Foucher, K. C., Andriacchi, T. P. 2003; 36 (1): 113-119

  Abstract

  An analytical parametric model was developed to estimate the natural biological variations in muscle forces and their effect on the hip forces subject only to physiological constraints and not predefined optimization criterion. Force predictions are based on the joint kinematics and kinetics of each subject, a previously published muscle model, and physiological constraints on the muscle force distributions. The model was used to determine the hip contact forces throughout the stance phase of gait of a subject with a total hip replacement (THR). The parametrically modeled peak hip force without antagonistic muscle activity varied from 2.7 to 3.2 Body Weights (mean 2.9 Body Weights), which agreed well with published in vivo measurements from instrumented THRs in other subjects. For every 10% increase in antagonistic activity, the mean peak hip force increased by 0.2 Body Weights. The parametric model allows one to examine the effect of specific muscle weaknesses or increased antagonistic muscle activity on the hip forces. The model also provides a tool for studying the effect of gait adaptations on hip forces, as predictions are based on each individual's gait data. Differences in peak forces between subjects can then be evaluated relative to the uncertainty in not knowing the precise muscle force distributions.

  View details for Web of Science ID 000180688700013

  View details for PubMedID 12485645

• Comparison of clinical and dynamic knee function in patients with anterior cruciate ligament deficiency AMERICAN JOURNAL OF SPORTS MEDICINE Patel, R. R., Hurwitz, D. E., Bush-Joseph, C. A., Bach, B. R., Andriacchi, T. P. 2003; 31 (1): 68-74

  Abstract

  Whether passive measures of isokinetic muscle strength deficits and knee laxity are related to the dynamic function of the anterior cruciate ligament-deficient knee remains unclear.Arthrometer measurements are not predictive of peak external knee flexion moment (net quadriceps muscle moment), isokinetic quadriceps muscle strength correlates with peak external knee flexion moment (net quadriceps muscle moment), and isokinetic hamstring muscle strength correlates with peak external knee extension moment (net flexor muscle moment).Cross-sectional study.Gait analysis was used to assess dynamic function during walking, jogging, and stair climbing in 44 subjects with unilateral anterior cruciate ligament deficiency and 44 control subjects. Passive knee laxity and isokinetic quadriceps and hamstring muscle strength were also measured.Arthrometer measurements did not correlate with peak external flexion or extension moments in any of the activities tested or with isokinetic quadriceps or hamstring muscle strength. Test subjects also had a significantly reduced peak external flexion moment during all three jogging activities and stair climbing compared with the control subjects and this was correlated with significantly reduced quadriceps muscle strength.Absolute knee laxity difference did not correlate with dynamic knee function as assessed by gait analysis and should not be used as a sole predictor for the outcome of treatment. Patients with greater than normal strength in the anterior cruciate ligament-deficient limb performed low- and high-stress activities in a more normal fashion than those with normal or less-than-normal strength.

  View details for Web of Science ID 000180473300012

  View details for PubMedID 12531760

• Risk factors for progressive cartilage loss in the knee: a longitudinal magnetic resonance imaging study in forty-three patients. Arthritis and rheumatism Biswal, S., Hastie, T., Andriacchi, T. P., Bergman, G. A., Dillingham, M. F., Lang, P. 2002; 46 (11): 2884-2892

  Abstract

  To evaluate the rate of progression of cartilage loss in the knee joint using magnetic resonance imaging (MRI) and to evaluate potential risk factors for more rapid cartilage loss.We evaluated baseline and followup MRIs of the knees in 43 patients (minimum time interval of 1 year, mean 1.8 years, range 52-285 weeks). Cartilage loss was graded in the anterior, central, and posterior regions of the medial and lateral knee compartments. Knee joints were also evaluated for other pathology. Data were analyzed using analysis of variance models.Patients who had sustained meniscal tears showed a higher average rate of progression of cartilage loss (22%) than that seen in those who had intact menisci (14.9%) (P

  View details for PubMedID 12428228

• Backsurface wear and deformation in polyethylene tibial inserts retrieved postmortem Annual Meeting of the Knee-Society/Association of-Hip-and-Knee-Surgeons Surace, M. F., Berzins, A., Urban, R. M., Jacobs, J. J., Berger, R. A., Natarajan, R. N., Andriacchi, T. P., Galante, J. O. SPRINGER. 2002: 14–23

  View details for Web of Science ID 000179273100004

• Risk factors for progressive cartilage loss in the knee ARTHRITIS AND RHEUMATISM Biswal, S., Hastie, T., Andriacchi, T. P., Bergman, G. A., Dillingham, M. F., Lang, P. 2002; 46 (11): 2884-2892

  View details for DOI 10.1002/art.10573

  View details for Web of Science ID 000179239500008

• Coventry Award paper. Backsurface wear and deformation in polyethylene tibial inserts retrieved postmortem. Clinical orthopaedics and related research Surace, M. F., Berzins, A., Urban, R. M., Jacobs, J. J., Berger, R. A., Natarajan, R. N., Andriacchi, T. P., Galante, J. O. 2002: 14-23

  Abstract

  Wear and deformation were characterized at the backsurface of 25 posterior cruciate-retaining total knee arthroplasty polyethylene inserts retrieved postmortem from 20 subjects. The mean implantation time was 64.1 months (range, 4-156 months). The backsurface of the inserts was inspected using a stereomicroscope with a digital optical system. Coronal histologic sections of 13 proximal tibias were inspected for the presence and extent of penetration of granuloma. Damage to the backsurface was limited. Polishing was recorded on 21 (84%) of the inserts and abrasive wear on five (20%) inserts. Pitting was present in 21 (84%) components, but involved less than 1% of the area in all but one of these components. Delamination and cracking were not observed. Extrusions were seen in all 10 of the components that had screw holes in the tibial tray. A correlation was found between the depth of penetration of the granuloma along the posteromedial screw and the height of the corresponding extrusion. The anteroposterior profiles showed a concave deformation of the backsurface in 24 (96 %) of the cases. The concave deformation of tibial inserts may facilitate accumulation and transportation of wear debris to the tibial bone-implant interface through the screw holes in implants designed for cementless fixation.

  View details for PubMedID 12439232

• Surface damage in machined ram-extruded and net-shape molded retrieved polyethylene tibial inserts of total knee replacements JOURNAL OF BONE AND JOINT SURGERY-AMERICAN VOLUME Berzins, A., Jacobs, J. J., Berger, R., Ed, C., Natarajan, R., Andriacchi, T., Galante, J. O. 2002; 84A (9): 1534-1540

  View details for Web of Science ID 000178016100005

• Surface damage in machined ram-extruded and net-shape molded retrieved polyethylene tibial inserts of total knee replacements. journal of bone and joint surgery. American volume Berzins, A., Jacobs, J. J., Berger, R., Ed, C., Natarajan, R., Andriacchi, T., Galante, J. O. 2002; 84-A (9): 1534-1540

  Abstract

  Polyethylene wear has emerged as a major determining factor in the long-term clinical performance of total knee replacements. This study addresses the in vivo wear performance of two types of polyethylene tibial inserts used in similar total knee arthroplasty designs.A surface damage assessment of retrieved specimens was performed for twenty-six net-shape molded tibial inserts manufactured from H1900 resin without calcium stearate additive (Miller-Galante) and forty-three machined ram-extruded tibial inserts manufactured from GUR 4150 resin with calcium stearate additive (Miller-Galante II). Stereomicroscopic inspection and digital image analysis were used to quantify the extent and severity of pitting, dimensional change, and delamination.Pitting and dimensional change were the most common modes of damage in both groups, with the prevalence ranging from 77% to 92% for pitting and from 51% to 81% for dimensional change. Delamination was the least common mode of damage, with the prevalence ranging from 21% to 35%. The severity of pitting was higher in association with the cemented implant-bone interface. The extent and severity of delamination increased with implantation time. No severe delamination was observed before sixty months after implantation in the net-shape molded group, whereas severe delamination was present as early as ten months after implantation in the machined ram-extruded group. The time between surgery and the discovery of damage was longer in the net-shape molded group for all modes of damage except for medial dimensional change.On the basis of the components available in our implant retrieval pool, we found that at equivalent levels of surface damage, the net-shape molded H1900 resin tibial inserts demonstrated longer service life than did the machined ram-extruded GUR 4150 components. The superior performance of the net-shape molded components may be related to the resin type, the absence of calcium stearate, the consolidation method, or the method of final geometry shaping. This superior damage resistance is expected to contribute to superior long-term clinical performance of net-shape molded ultra-high molecular weight polyethylene in total knee arthroplasty.

  View details for PubMedID 12208909

• Increased knee joint loads during walking are present in subjects with knee osteoarthritis OSTEOARTHRITIS AND CARTILAGE Baliunas, A. J., Hurwitz, D. E., Ryals, A. B., Karrar, A., CASE, J. P., Block, J. A., Andriacchi, T. P. 2002; 10 (7): 573-579

  Abstract

  This study tests the hypothesis that the peak external knee adduction moment during gait is increased in a group of ambulatory subjects with knee osteoarthritis (OA) of varying radiographic severity who are being managed with medical therapy. Tibiofemoral knee OA more commonly affects the medial compartment. The external knee adduction moment can be used to assess the load distribution between the medial and lateral compartments of the knee joint. Additionally, this study tests if changes in the knee angles, such as a reduced midstance knee flexion angle, or reduced sagittal plane moments previously identified by others as load reducing mechanisms are present in this OA group.Thirty-one subjects with radiographic evidence of knee OA and medial compartment cartilage damage were gait tested after a 2-week drug washout period. Thirty-one normal subjects (asymptomatic control subjects) with a comparable age, weight and height distribution were also tested. Significant differences in the sagittal plane knee motion and peak external moments between the normal and knee OA groups were identified using t tests.Subjects with knee OA walked with a greater than normal peak external knee adduction moment (P=0.003). The midstance knee flexion angle was not significantly different between the two groups (P=0.625) nor were the peak flexion and extension moments (P> 0.037).Load reducing mechanisms, such as a decreased midstance knee flexion angle, identified by others in subjects with endstage knee OA or reduced external flexion or extension moments were not present in this group of subjects with knee OA who were being managed by conservative treatment. The finding of a significantly greater than normal external knee adduction moment in the knee OA group lends support to the hypothesis that an increased knee adduction moment during gait is associated with knee OA.

  View details for DOI 10.1053/joca.2002.0797

  View details for Web of Science ID 000177625700010

  View details for PubMedID 12127838

• Mechanical loads at the knee joint during deep flexion JOURNAL OF ORTHOPAEDIC RESEARCH Nagura, T., Dyrby, C. O., Alexander, E. J., Andriacchi, T. P. 2002; 20 (4): 881-886

  Abstract

  There is a lack of fundamental information on the knee biomechanics in deep flexion beyond 90 degrees. In this study, mechanical loads during activities requiring deep flexion were quantified on normal knees from 19 subjects, and compared with those in walking and stair climbing. The deep flexion activities generate larger net quadriceps moments (6.9-13.5% body weight into height) and net posterior forces (58.3-67.8% body weight) than routine ambulatory activities. Moreover, the peak net moments and the net posterior forces were generated between 90 degrees and 150 degrees of flexion. The large moments and forces will result in high stress at high angles of flexion. These loads can influence pathological changes to the joint and are important considerations for reconstructive procedures of the knee. The posterior cruciate ligament should have a substantial role during deep flexion, since there was a large posterior load that must be sustained at the knee. The mechanics of the knee in deep flexion are likely a factor causing problems of posterior instability in current total knee arthroplasty. Thus, it is important to consider the magnitude of the loads at the knee in the treatment of patients that commonly perform deep flexion during activities of daily living.

  View details for Web of Science ID 000177191600034

  View details for PubMedID 12168682

• Quantitative analysis of the relative effectiveness of 3 iliotibial band stretches ARCHIVES OF PHYSICAL MEDICINE AND REHABILITATION Fredericson, M., White, J. J., MacMahon, J. M., Andriacchi, T. P. 2002; 83 (5): 589-592

  Abstract

  To compare the relative effectiveness of 3 common standing stretches for the iliotibial band (ITB): arms at side (stretch A), arms extending overhead (stretch B), and arms reaching diagonally downward (stretch C).Each subject's biomechanics was captured as a 3-dimensional image by using a 4-camera gait acquisition system with a forceplate.University biomotion laboratory.Five male elite-level distance runners.All participants performed each of the 3 standing stretches for the ITB.For each stretch, change in ITB tissue length and the force generated within the stretched complex was measured. Data were then combined and analyzed by using kinetic values assessment.All 3 stretches created statistically significant changes in ITB length (P<.05), but stretch B, incorporating overhead arm extension, was consistently most effective both for average ITB length change and average adduction moments at the hip and knee.Adding an overhead arm extension to the most common standing ITB stretch may increase average ITB length change and average external adduction moments in elite-level distance runners.

  View details for DOI 10.1053/apmr.2002.31606

  View details for Web of Science ID 000175494000001

  View details for PubMedID 11994795

• Failure and fatigue characteristics of adhesive athletic tape MEDICINE AND SCIENCE IN SPORTS AND EXERCISE Bragg, R. W., MacMahon, J. M., Overom, E. K., Yerby, S. A., Matheson, G. O., Carter, D. R., Andriacchi, T. P. 2002; 34 (3): 403-410

  Abstract

  Athletic tape has been commonly reported to lose much of its structural support after 20 min of exercise. Although many studies have addressed the functional performance characteristics of athletic tape, its mechanical properties are poorly understood. This study examines the failure and fatigue properties of several commonly used athletic tapes.A Web-based survey of professional sports trainers was used to select the following three tapes for the study: Zonas (Johnson & Johnson), Leukotape (Beiersdorf), and Jaylastic (Jaybird & Mais). Using a hydraulic material testing system (MTS), eight samples of each tape were compared in three different mechanical tests: load-to-failure, fatigue testing under load control, and fatigue testing under displacement control. Differences in tape microstructure were used to interpret the results of the mechanical tests.Significant differences (P < 0.001) in failure load, elongation at failure, and stiffness were found from failure tests. Significant differences were also found (P < 0.001) in fatigue behavior under both modes of control. As a representative example, in one normalized displacement control fatigue test after 20 min of cycling, 21% (Zonas), 29% (Leukotape), and 57% (Jaylastic) of the mechanical support was lost. After cycling, all tapes loaded to failure showed increased stiffness (P < 0.001), indicating significant energy absorption during cycling. Observed differences in the tapes' microstructure were qualitatively consistent with the measured differences in their mechanical properties.In understanding the shortcomings of currently available tapes, the results of these tests can now be used as benchmarks with which to compare and develop future tape designs. Ultimately, these improved tapes should reduce ankle injuries among athletes.

  View details for Web of Science ID 000174268300004

  View details for PubMedID 11880802

• The knee adduction moment during gait in subjects with knee osteoarthritis is more closely correlated with static alignment than radiographic disease severity, toe out angle and pain JOURNAL OF ORTHOPAEDIC RESEARCH Hurwitz, D. E., Ryals, A. B., CASE, J. P., Block, J. A., Andriacchi, T. P. 2002; 20 (1): 101-107

  Abstract

  This study tested whether the peak external knee adduction moments during walking in subjects with knee osteoarthritis (OA) were correlated with the mechanical axis of the leg, radiographic measures of OA severity, toe out angle or clinical assessments of pain, stiffness or function. Gait analysis was performed on 62 subjects with knee OA and 49 asymptomatic control subjects (normal subjects). The subjects with OA walked with a greater than normal peak adduction moment during early stance (p = 0.027). In the OA group, the mechanical axis was the best single predictor of the peak adduction moment during both early and late stance (R = 0.74, p < 0.001). The radiographic measures of OA severity in the medial compartment were also predictive of both peak adduction moments (R = 0.43 to 0.48, p < 0.001) along with the sum of the WOMAC subscales (R = -0.33 to -0.31, p < 0.017). The toe out angle was predictive of the peak adduction moment only during late stance (R = -0.45, p < 0.001). Once mechanical axis was accounted for, other factors only increased the ability to predict the peak knee adduction moments by 10 18%. While the mechanical axis was indicative of the peak adduction moments, it only accounted for about 50% of its variation, emphasizing the need for a dynamic evaluation of the knee joint loading environment. Understanding which clinical measures of OA are most closely associated with the dynamic knee joint loads may ultimately result in a better understanding of the disease process and the development of therapeutic interventions.

  View details for Web of Science ID 000173353800014

  View details for PubMedID 11853076

• Dynamic function and imaging in the analysis of osteoarthritis at the knee Conference on the Many Faces of Osteoarthritis Andriacchi, T. P. BIRKHAUSER VERLAG AG. 2002: 443–452

  View details for Web of Science ID 000181203200052

• Linking the biology of osteoarthritis to locomotion mechanics Conference on the Many Faces of Osteoarthritis Thonar, E. J., Hurwitz, D. E., Andriacchi, T. P., Lenz, M. E., Sharma, L. BIRKHAUSER VERLAG AG. 2002: 453–460

  View details for Web of Science ID 000181203200053

• Correcting for deformation in skin-based marker systems JOURNAL OF BIOMECHANICS Alexander, E. J., Andriacchi, T. P. 2001; 34 (3): 355-361

  Abstract

  A new technique is described that reduces error due to skin movement artifact in the opto-electronic measurement of in vivo skeletal motion. This work builds on a previously described point cluster technique marker set and estimation algorithm by extending the transformation equations to the general deformation case using a set of activity-dependent deformation models. Skin deformation during activities of daily living are modeled as consisting of a functional form defined over the observation interval (the deformation model) plus additive noise (modeling error). The method is described as an interval deformation technique. The method was tested using simulation trials with systematic and random components of deformation error introduced into marker position vectors. The technique was found to substantially outperform methods that require rigid-body assumptions. The method was tested in vivo on a patient fitted with an external fixation device (Ilizarov). Simultaneous measurements from markers placed on the Ilizarov device (fixed to bone) were compared to measurements derived from skin-based markers. The interval deformation technique reduced the errors in limb segment pose estimate by 33 and 25% compared to the classic rigid-body technique for position and orientation, respectively. This newly developed method has demonstrated that by accounting for the changing shape of the limb segment, a substantial improvement in the estimates of in vivo skeletal movement can be achieved.

  View details for Web of Science ID 000167482500009

  View details for PubMedID 11182127

• Dynamic function after anterior cruciate ligament reconstruction with autologous patellar tendon AMERICAN JOURNAL OF SPORTS MEDICINE Bush-Joseph, C. A., Hurwitz, D. E., Patel, R. R., Bahrani, Y., Garretson, R., Bach, B. R., Andriacchi, T. P. 2001; 29 (1): 36-41

  Abstract

  The purpose of this study was to dynamically assess the functional outcome of patients who had undergone successful anterior cruciate ligament reconstruction using an autologous patellar tendon technique and to determine whether their dynamic knee function was related to quadriceps and hamstring muscle strength. The knee kinematics and kinetics of 22 subjects who had undergone anterior cruciate ligament reconstruction (mean age, 27 +/- 11 years) and of 22 age- and sex-matched healthy control subjects were determined during various dynamic activities using a computerized motion analysis and force plate system. The differences in the sagittal plane angles and external moments between the two groups during light (walking), moderate (climbing and descending stairs), and higher-demand (jogging, jog and cut, jog and stop) activities were related to isokinetic strength measurements. Although patients who are asymptomatic and functioning well after anterior cruciate ligament reconstruction can perform normally in light activities, higher-demand activities reveal persistent functional adaptations that require further study.

  View details for Web of Science ID 000166779200008

  View details for PubMedID 11206254

• Functional gait adaptations in patients with painful hip REVUE DE CHIRURGIE ORTHOPEDIQUE ET REPARATRICE DE L APPAREIL MOTEUR Hulet, C., Hurwitz, D. E., Andriacchi, T. P., Galante, J. O., Vielpeau, C. 2000; 86 (6): 581-589

  Abstract

  This prospective study was conducted to analyze the mechanisms of gait compensation in patients with painful hip and to search for correlations with preoperative clinical and radiographic findings.Optoelectronic and multicomponent force-plate datas were used to calculate joint motion, moments and intersegmental forces for 26 patients with unilateral hip pain and 20 normal age and sex-matched patients. Height was similar in the two groups but mean weight in the study group (83 kg) was greater than in the controls (68 kg). The preoperative Harris score was 53 in the study group and 16 patients had a permanent flexion contracture of the knee (mean 15 degrees, range 5-30 degrees). Radiographically, there were 22 cases of osteo-arthritis hip disease and 4 cases of necrosis.Gait analysis showed a significant 0.66 +/- 0.06 m (12 p. 100) reduction in step length. Patients who had severe hip pain walked with a decreased dynamic range of motion (18 +/- 5 degrees, p<0.0001) with a curve reversal as they extended the hip. They also reduced dynamic range of motion of the knee and ankle. Patients who presented a reversal in their dynamic hip range of motion had a greater passive flexion contracture and a greater loss in range of motion during gait than those with a smooth regular pattern (p<0.0001). Patients with hip pain walked with significantly decreased external extension, adduction, and internal and external rotation moments (p<0.0001). They also unloaded the ipsilateral knee and ankle. The decreased hip extension moment was significantly correlated with an increased level of pain (p<0.0001). There was no correlation with radiological findings.Reversal of dynamic hip range of motion was interpreted as a mechanism to increase effective hip extension during stance phase through increased anterior pelvic tilt and lumbar lordosis.Patients with painful hip walked with a manner that was asymmetric. These gait modifications were related to hip limitation in passive motion and pain. Patients with flexion contracture adopted a compensatory gait mechanism. This study confirms relation between hip pain and forces across the hip joint.

  View details for Web of Science ID 000165281500005

  View details for PubMedID 11060432

• Studies of human locomotion: past, present and future XVII Congress of the International-Society-of-Biomechanics Andriacchi, T. P., Alexander, E. J. ELSEVIER SCI LTD. 2000: 1217–24

  Abstract

  The study of human locomotion and its applications are examined from a historical viewpoint. Several critical steps in the advancement of the discipline are considered in the context of addressing a particular need to answer fundamental questions regarding the process of human locomotion. In addition, changes in the methods of observation are discussed in terms of the advancement of the field. As an example, the application of a newly developed point cluster technique to reduce the artifact due to skin movement is described. The method was applied to a study of patients with anterior cruciate ligament (ACL) deficient knees. The results demonstrate that patients with ACL-deficient knees have significantly greater than normal anterior-posterior displacement of the femur relative to the tibia during walking. Many of the advancements in the tools for observation and interpretation have been driven by new demands on our fundamental knowledge. Future advancements in the study of human locomotion will likely be motivated by new treatment modalities that require an in depth understanding of the subtle complexities of human locomotion. Future directions are discussed in the context of new methods for reducing errors associated with skin movement combined with information obtained from other imaging methods, such as magnetic resonance imaging.

  View details for Web of Science ID 000089304700005

  View details for PubMedID 10899330

• Knee pain and joint loading in subjects with osteoarthritis of the knee JOURNAL OF ORTHOPAEDIC RESEARCH Hurwitz, D. E., Ryals, A. R., Block, J. A., Sharma, L., Schnitzer, T. J., Andriacchi, T. P. 2000; 18 (4): 572-579

  Abstract

  Although treatments for osteoarthritis of the knee are often directed at relieving pain, pain may cause patients to alter how they perform activities to decrease the loads on the joints. The knee-adduction moment is a major determinant of the load distribution between the medial and lateral plateaus. Therefore, the interrelationship between pain and the external knee-adduction moment during walking may be especially important for understanding mechanical factors related to the progression of medial tibiofemoral osteoarthritis. Fifty-three subjects with symptomatic radiographic evidence of osteoarthritis of the knee were studied. These subjects were a subset of those enrolled in a double-blind study in which gait analysis and radiographic and clinical evaluations were performed after a 2-week washout of anti-inflammatory and analgesic treatment. The subjects then took a nonsteroidal anti-inflammatory drug, acetaminophen, or placebo for 2 weeks, and the gait and clinical evaluations were repeated. The change in the peak external adduction moment between the two evaluations was inversely correlated with the change in pain (R = 0.48, p < 0.001) and was significantly different between those whose pain increased (n = 7), decreased (n = 18), or remained unchanged (n = 28) (p = 0.009). Those with increased pain had a significant decrease in the peak external adduction (p = 0.005) and flexion moments (p = 0.023). In contrast, the subjects with decreased pain tended to have an increase in the peak external adduction moment (p = 0.095) and had a significant increase in the peak external extension moment (p = 0.017). The subjects whose pain was unchanged had no significant change in the peak external adduction (p = 0.757), flexion (p = 0.234), or extension (p = 0.465) moments. Thus, decreases in pain among patients with medial tibiofemoral osteoarthritis were related to increased loading of the degenerative portion of the joints. Additional long-term prospective studies are needed to determine whether increased loading during walking actually results in accelerated progression of the disease.

  View details for Web of Science ID 000089921300008

  View details for PubMedID 11052493

• Abnormalities in muscle function during gait in relation to the level of lumbar disc herniation SPINE Morag, E., Hurwitz, D. E., Andriacchi, T. P., Hickey, M., Andersson, G. B. 2000; 25 (7): 829-833

  Abstract

  A comparison between gait in patients undergoing surgery for L4 and L5 lumbar disc herniations and that in an age- and weight-matched control group.To study whether changes in the moments produced at the ankle and knee joints during walking reflect the neurologic level of a herniated nucleus pulposus.Lumbar herniated discs often cause muscle weakness, reduced motor function, and change in walking capacity. The specific effects of a disc herniation on muscle function during gait is poorly documented.Conventional physical examination and kinetic analysis of gait were performed on 16 patients who subsequently underwent surgery for herniated discs (eight with L4-L5 and eight with L5-S1 disc herniations) and 16 healthy control subjects. The three components of the external moment at the ankle and knee were computed. The peak magnitudes of specific components of the external moments were compared with those of the control group.Reduced external ankle plantar flexion moment, indicating a decreased function of the ankle dorsiflexors, was found in patients with herniated nucleus pulposus of both L4-L5 and L5-S1. Reduced external ankle dorsiflexion moment, indicating a decreased function of the ankle plantar flexors, was found only in patients with a lesion to the L5-S1 disc, but not in those with herniations at L4-L5.Preoperative gait analysis identified functional deficits of the muscles about the ankle and foot that relate to the level of the herniation. Kinetic measurements can assist in understanding the functional limitations associated with specific levels of a herniation.

  View details for Web of Science ID 000086483100013

  View details for PubMedID 10751294

• Methodology for long-term wear testing of total knee replacements CLINICAL ORTHOPAEDICS AND RELATED RESEARCH Walker, P. S., Blunn, G. W., Perry, J. P., Bell, C. J., Sathasivam, S., Andriacchi, T. P., Paul, J. P., Haider, H., Campbell, P. A. 2000: 290-301

  Abstract

  This article begins to address the validation requirements of wear testing on total knee replacements in a knee simulator. The knee simulator has four stations. The axial force is variable but reaches a maximum of 2.3 kN. Physiologic anteroposterior shear force and rotational torques are supplied to the knee. The forces and displacements are timed to coincide with those of a typical gait cycle. Kinematics of the simulator are dependent on the type of knee being tested. Tests of designs with well known clinical histories were done to 10 million cycles. The relative amounts and types of wear shown by the designs were similar to that found in their clinical histories. Wear tracks on more conforming designs were larger, and the penetration into the plastic appeared to be less. This did not necessarily mean that wear, as measured by loss of material, was reduced on conforming designs. Delamination of the plastic was achieved only after aging the tibial components. Wear particles isolated from the lubricating fluid were similar in size and shape to those isolated from in vivo specimens. However, the relative amounts of wear particle shapes were different depending on the design. At the start of the tests, all of the flexibly mounted tibial components showed more motion than after 5 million cycles, indicating that the surface of the plastic became more conforming. This study showed that knee wear similar to wear observed in vivo can be reproduced in the laboratory. The parameters and methods elucidated in this introductory study should form the basis for use in preclinical wear tests of total knee replacements.

  View details for Web of Science ID 000085864200032

  View details for PubMedID 10738439

• Methods for evaluating the progression of osteoarthritis JOURNAL OF REHABILITATION RESEARCH AND DEVELOPMENT Andriacchi, T. P., Lang, P. L., Alexander, E. J., Hurwitz, D. E. 2000; 37 (2): 163-170

  Abstract

  This article discusses methods for evaluating the progression of osteoarthritis through dynamic functional imaging as opposed to current static techniques. Comparison is made between static and dynamic methods of evaluating knee alignment. The correlation between dynamic knee moments during gait and bone mineral content is discussed. Knee loading is considered in terms of high tibial osteotomy, knee braces, pain, and non-steroidal anti-inflammatory drugs. New image-processing techniques for quantitating cartilage loss are described, and computational methods for generating true three-dimensional (3-D) maps of cartilage thickness are developed. Finally, new approaches to cross-correlate magnetic resonance images with kinematic measurements are described. These new techniques promise to become powerful diagnostic tools to detect and characterize pathological load distributions across articular cartilage.

  View details for Web of Science ID 000165733400009

  View details for PubMedID 10850822

• Characterization of gait parameters in patients with Charcot-Marie-Tooth disease NEUROLOGY INDIA Kuruvilla, A., Costa, J. L., WRIGHT, R. B., Yoder, D. M., Andriacchi, T. P. 2000; 48 (1): 49-55

  Abstract

  The gait of five patients with Charcot-Marie-Tooth(CMT) disease was analyzed using light-emitting diodes and a force plate. The flexion-extension motions of the hips, knees, and ankles, as well as their moments (vector sums of forces acting at the joints) in the flexion-extension and abduction-adduction planes, were quantified. The gait of the CMT patients showed abnormalities consistent with both distal weakness (ankle dorsi- and plantar-flexors) and weakness of the hip abductor muscles. The latter weakness appeared to produce asymmetric hip moments and truncal instability in the mediolateral plane during ambulation. However, the extent to which the gait was abnormal appeared not to be exclusively related to the severity of the sensorimotor conduction deficits in the peripheral nerves. In the four patients for whom nerve conduction velocity studies were available, decrease in the lower-extremity distal conduction velocities and evoked motor amplitude potentials did not correlate with the severity and extent of the gait abnormalities.

  View details for Web of Science ID 000086991700010

  View details for PubMedID 10751814

• Functional adaptations in patients with ACL-deficient knees Workshop on the Role of Proprioception and Neuromuscular Control in the Management and Rehabilitation of Joint Pathology Andriacchi, T. P., Hurwitz, D. E., Bush-Joseph, C. A., Bach, B. R. HUMAN KINETICS PUBL. 2000: 181–188

  View details for Web of Science ID 000087293100019

• Dynamic functional joint imaging 14th International Congress and Exhibition on Computer Assisted Radiology and Surgery (CARS 2000) Alexander, E. J., Lang, P. K., Andriacchi, T. P., Steines, D. ELSEVIER SCIENCE BV. 2000: 303–308

  View details for Web of Science ID 000165685600051

• A functionally based 3-D coordinate system of the knee for diagnostic use and preoperative planning 14th International Congress and Exhibition on Computer Assisted Radiology and Surgery (CARS 2000) MacMahon, J. M., Alexander, E. J., MacMahon, E. B., Andriacchi, T. P. ELSEVIER SCIENCE BV. 2000: 208–213

  View details for Web of Science ID 000165685600034

• Effect of knee pain on joint loading in patients with osteoarthritis. Current opinion in rheumatology Hurwitz, D. E., Sharma, L., Andriacchi, T. P. 1999; 11 (5): 422-426

  Abstract

  Treatment of patients with osteoarthritis is often directed at relieving pain and restoring function. Pain, however, may serve as a protective mechanism in that patients may decrease their levels of activity or alter the manner in which they perform activities in response to pain. Pain reduction may result in increased loads on the joints during dynamic activities, which may result in more rapid disease progression. Therefore, treatment methods that relieve pain but result in a loss of the protective mechanisms associated with pain may not be beneficial in the long term. This mechanism of decreased pain associated with an overuse of the degenerated joint has been referred to as an "analgesic arthropathy." This article discusses common treatments or interventions used for patients with knee osteoarthritis and their potential effects on pain levels and loads at the knee joint during walking. Understanding the relationship between treatment methods, pain, and the knee joint loads during walking is important because walking is the most frequently performed activity, and the cyclic loads at the knee joint during walking are high.

  View details for PubMedID 10503665

• Study on effect of graded facetectomy on change in lumbar motion segment torsional flexibility using three-dimensional continuum contact representation for facet joints JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME Natarajan, R. N., Andersson, G. B., Patwardhan, A. G., Andriacchi, T. P. 1999; 121 (2): 215-221

  Abstract

  Facet joints provide rigidity to the lumbar motion segment and thus protect the disk, particularly against torsional injury. A surgical procedure that fully or partially removes the facet joints (facetectomy) will decrease the mechanical stiffness of the motion segment, and potentially place the disk at risk of injury. Analytical models can be used to understand the effect of facet joints on motion segment stability. Using a facet joint model that represents the contact area as contact between two surfaces rather than as point contact, it was concluded that a substantial sudden change in rotational motion, due to applied torsion moment, was observed after 75 percent of any one of the facet joints was removed. Applied torsional moment loading produced coupled extension motion in the intact motion segment. This coupled motion also experienced a large change following complete unilateral facetectomy. Clinically, the present study showed that surgical intervention in the form of unilateral or bilateral total facetectomy might require fusion to reduce the primary torsion motion.

  View details for Web of Science ID 000079930400011

  View details for PubMedID 10211456

• A point cluster method for in vivo motion analysis: applied to a study of knee kinematics. Journal of biomechanical engineering Andriacchi, T. P., Alexander, E. J., Toney, M. K., Dyrby, C., Sum, J. 1998; 120 (6): 743-749

  Abstract

  A new method for deriving limb segment motion from markers placed on the skin is described. The method provides a basis for determining the artifact associated with nonrigid body movement of points placed on the skin. The method is based on a cluster of points uniformly distributed on the limb segment. Each point is assigned an arbitrary mass. The center of mass and the inertia tensor of this cluster of points are calculated. The eigenvalues and eigenvectors of the inertia tensor are used to define a coordinate system in the cluster as well as to provide a basis for evaluating non-rigid body movement. The eigenvalues of the inertia tensor remain invariant if the segment is behaving as a rigid body, thereby providing a basis for determining variations for nonrigid body movement. The method was tested in a simulation model where systematic and random errors were introduced into a fixed cluster of points. The simulation demonstrated that the error due to nonrigid body movement could be substantially reduced. The method was also evaluated in a group of ten normal subjects during walking. The results for knee rotation and translation obtained from the point cluster method compared favorably to results previously obtained from normal subjects with intra-cortical pins placed into the femur and tibia. The resulting methodology described in this paper provides a unique approach to the measurement of in vivo motion using skin-based marker systems.

  View details for PubMedID 10412458

• Vivo motion analysis: Applied to a study of knee kinematics JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME Andriacchi, T. P., Alexander, E. J., Toney, M. K., Dyrby, C. 1998; 120 (6): 743-749

  View details for Web of Science ID 000077716900009

• Hip motion and moments during gait relate directly to proximal femoral bone mineral density in patients with hip osteoarthritis JOURNAL OF BIOMECHANICS Hurwitz, D. E., Foucher, K. C., Sumner, D. R., Andriacchi, T. P., Rosenberg, A. G., Galante, J. O. 1998; 31 (10): 919-925

  Abstract

  The present study examined the loads at the hip joint during gait and the bone mineral density of the proximal femur in 25 patients with end-stage hip osteoarthritis. Dual energy X-ray absorptiometry was used to determine the bone mineral density of the greater trochanter, femoral neck and Ward's triangle of the osteoarthritic group. The bone mineral density was normalized for the patient's age, gender, weight and ethnic origin (Z score). Gait analysis was used to determine the external hip joint moments and motion during walking for the osteoarthritic group and a control group of 21 normal subjects. The gait parameters of the osteoarthritic group which were significantly diminished compared to the normal group (p < 0.001) accounted for as much as 42% (p < 0.001) of the variation in the normalized bone mineral density. Specifically, the dynamic sagittal plane hip motion during gait (maximum flexion minus maximum extension) and peak external rotation and adduction moments were significantly correlated with greater trochanter (R = 0.429-0.648, p = 0.032-0.0001) and Ward's triangle (R = 0.418-0.532, p = 0.038-0.006) normalized bone mineral density while the adduction moment was also significantly correlated with the femoral neck normalized bone mineral density (R = 0.5394, p = 0.005). The normalized bone mineral density of the femoral neck and Ward's triangle was elevated while that of the greater trochanter was decreased as compared to normal reference values. The significant correlation between the hip joint moments during gait and femoral bone mineral density indicate that hip joint loads need to be included when explaining local variation in bone mineral density in hip osteoarthritis.

  View details for Web of Science ID 000077061600007

  View details for PubMedID 9840757

• Knee adduction moment, serum hyaluronan level, and disease severity in medial tibiofemoral osteoarthritis ARTHRITIS AND RHEUMATISM Sharma, L., Hurwitz, D. E., Thonar, E. J., Sum, J. A., Lenz, M. E., Dunlop, D. D., Schnitzer, T. J., Kirwan-Mellis, G., Andriacchi, T. P. 1998; 41 (7): 1233-1240

  Abstract

  The adduction moment at the knee during gait is the primary determinant of medial-to-lateral load distribution. If the adduction moment contributes to progression of osteoarthritis (OA), then patients with advanced medial tibiofemoral OA should have higher adduction moments. The present study was undertaken to investigate the hypothesis that the adduction moment normalized for weight and height is associated with medial tibiofemoral OA disease severity after controlling for age, sex, and pain level, and to examine the correlation of serum hyaluronan (HA) level with disease severity and with the adduction moment in a subset of patients.Fifty-four patients with medial tibiofemoral OA underwent gait analysis and radiographic evaluation. Disease severity was assessed using the Kellgren-Lawrence (K-L) grade and medial joint space width. In a subset of 23 patients with available sera, HA was quantified by sandwich enzyme-linked immunosorbent assay. Pearson correlations, a random effects model, and multivariate regression models were used.The adduction moment correlated with the K-L grade in the left and right knees (r = 0.68 and r = 0.60, respectively), and with joint space width in the left and right knees (r = -0.45 and r = -0.47, respectively). The relationship persisted after controlling for age, sex, and severity of pain. The partial correlation between K-L grade and adduction moment was 0.71 in the left knees and 0.61 in the right knees. For every 1.0-unit increase in adduction moment, there was a 0.63-mm decrease in joint space width. In the subset of patients in whom serum HA levels were measured, HA levels correlated with medial joint space width (r = -0.55), but not with the adduction moment.There is a significant relationship between the adduction moment and OA disease severity. Serum HA levels correlate with joint space width but not with the adduction moment. Longitudinal studies will be necessary to determine the contribution of the adduction moment, and its contribution in conjunction with metabolic markers, to progression of medial tibiofemoral OA.

  View details for Web of Science ID 000074585400013

  View details for PubMedID 9663481

• Dynamic knee loads during gait predict proximal tibial bone distribution JOURNAL OF BIOMECHANICS Hurwitz, D. E., Sumner, D. R., Andriacchi, T. P., Sugar, D. A. 1998; 31 (5): 423-430

  Abstract

  This study tested the validity of the prediction of dynamic knee loads based on gait measurements. The relationship between the predicted loads at the knee and the distribution of bone between the medial and lateral sides of the tibia was examined. The motion and external forces and moments at the knee were measured during gait and a statically determinate muscle model was used to predict the corresponding forces on the medial and lateral tibial plateaus. In particular, the relationship between the knee adduction moment during gait and the ratio or distribution of medial to lateral tibial bone mineral content was studied. Bone mineral content was measured with dual energy X-ray absorptiometry in four regions, two proximal regions 20 mm in height, one medial and one lateral and two distal regions 20 mm in height, one medial and one lateral. The best single predictor of the medial lateral ratio of proximal bone mineral content (bone distribution) was the adduction moment (R2=0.31, p=0.003). Adding weight (negative coefficient. p=0.0004) and the ratio of the average predicted peak force on the medial plateau to the predicted peak force on the lateral plateau (positive coefficient, p=0.0033) to the regression model significantly increased the ability to predict the proximal medial lateral bone distribution (R2=0.72, p=0.0001). Distally neither the subject characteristics nor the gait moments and predicted forces were significant predictors of the bone distribution. The lack of a correlation distally may be reflective of the forces being more evenly distributed further from the tibial plateau. While it has long been suggested that the adduction moment is the primary determinate of the distribution of load between the medial and lateral plateaus, this is the first evidence of its relationship to the underlying bone distribution.

  View details for Web of Science ID 000075497300003

  View details for PubMedID 9727339

• Functional gait adaptations in patients with anterior cruciate ligament deficiency over time CLINICAL ORTHOPAEDICS AND RELATED RESEARCH Wexler, G., Hurwitz, D. E., Bush-Joseph, C. A., Andriacchi, T. P., Bach, B. R. 1998: 166-175

  Abstract

  Functional adaptations in knee kinematics and kinetics during level walking in 30 patients with unilateral anterior cruciate ligament deficiency and 30 healthy control subjects were studied. To examine the impact of time after injury on the functional adaptations, patients were placed into three time interval groups: early, intermediate, and chronic. The patients with anterior cruciate ligament deficiency had significantly decreased external knee flexion moments (balanced by net quadriceps contraction) and significantly increased external knee extension moments (balanced by net knee flexors contraction) as compared with the control subjects. As time after the injury increased, changes in the sagittal plane knee moments were more pronounced. A significant linear relationship (positive correlation) was found between the midstance knee flexion moment and the corresponding knee flexion angle. The patients with anterior cruciate deficiency had a greater knee flexion angle when generating a comparable midstance knee flexion moment as compared to the control subjects. The identification of gait adaptations over time provides additional information on the natural history of anterior cruciate ligament deficiency and may have implications regarding conservative rehabilitation, evaluation of outcomes, progression of meniscal injury, and the development of degenerative arthritis of the knee.

  View details for Web of Science ID 000072887000026

  View details for PubMedID 9553549

• Practical and theoretical considerations in the application in the development of clinical gait analysis BIO-MEDICAL MATERIALS AND ENGINEERING Andriacchi, T. P. 1998; 8 (3-4): 137-143

  View details for Web of Science ID 000078402500004

  View details for PubMedID 10065880

• A striated pattern of wear in ultrahigh-molecular-weight polyethylene components of Miller-Galante total knee arthroplasty JOURNAL OF ARTHROPLASTY Wimmer, M. A., Andriacchi, T. P., Natarajan, R. N., Loos, J., Karlhuber, M., Petermann, J., Schneider, E., Rosenberg, A. G. 1998; 13 (1): 8-16

  Abstract

  Wear of the polyethylene tibial components is a potential cause of failure in total knee arthroplasty. In addition to pitting, burnishing, and scratching, subtle striations on the bearing portion of the tibial surface have been observed in components retrieved relatively early after implantation. The striated pattern most typically occurred in areas centrally located within the articulating surface. The striations were anteroposterior directed and were identified as local cold flow at the surface. There was a strong correlation between the medial and lateral striated areas, suggesting that these patterns are related to cyclic rolling of the knee. The general characteristics and alignment of the striations could be attributed to the compressive and tractive forces occurring during femoral rollback. For the clinician, these results suggest that kinematics, as well as contact stress, should be considered when evaluating wear of polyethylene components.

  View details for Web of Science ID 000072498600002

  View details for PubMedID 9493532

• The influence of walking speed on mechanical joint power during gait GAIT & POSTURE Chen, I. H., Kuo, K. N., Andriacchi, T. P. 1997; 6 (3): 171-176

  View details for Web of Science ID A1997YG54200001

• Joint loading with valgus bracing in patients with varus gonarthrosis CLINICAL ORTHOPAEDICS AND RELATED RESEARCH Lindenfeld, T. N., Hewett, T. E., Andriacchi, T. P. 1997: 290-297

  Abstract

  The purpose of this study was to determine whether a brace designed to unload varus degenerative knees actually alters medial compartment loads by decreasing the adduction moment. Eleven patients who had arthrosis confined to the medial compartment were fitted with a valgus brace and tested before and after brace wear with pain and function scoring instruments and by automated gait analysis. The biomechanical data from these patients were compared with those from 11 healthy control subjects. Scores from an analog pain scale decreased 48% with brace wear, and function with activities of daily living increased 79%. Mean adduction moment without the brace measured 4.0 +/- 0.8% body weight times height versus 3.6 +/- 0.8% body weight times height when wearing the brace (10% decrease). The mean adduction moment for control subjects was 3.5 +/- 0.6% body weight times height. Thus, the mean adduction moment decreased from approximately one standard deviation from the normal mean to a value that is similar to the control value. Nine of 11 patients had a decrease in the adduction moment with the brace, five of 11 patients had a reduction higher than 10%, and decreases in this moment were as high as 32%. This study shows that pain, function, and biomechanical knee loading can be altered by a brace designed to unload the medial compartment of the knee.

  View details for Web of Science ID A1997YF26500029

  View details for PubMedID 9372780

• Gait biomechanics and total knee arthroplasty. The American journal of knee surgery Andriacchi, T. P., Hurwitz, D. E. 1997; 10 (4): 255-260

  View details for PubMedID 9421602

• Gait compensations in patients with osteoarthritis of the hip and their relationship to pain and passive hip motion JOURNAL OF ORTHOPAEDIC RESEARCH Hurwitz, D. E., Hulet, C. H., Andriacchi, T. P., Rosenberg, A. G. 1997; 15 (4): 629-635

  Abstract

  This study related mechanisms of gait compensations to the level of pain and to limitations in passive motion in patients with osteoarthritis of the hip. Joint motion, moments, and intersegmental forces were calculated for 19 patients with unilateral osteoarthritis of the hip (12 men and seven women) and for a group of normal subjects (12 men and seven women) with a similar age distribution. The patients who had osteoarthritis walked with a decreased dynamic range of motion (17 +/- 4 degrees) of the hip and with a hesitation or reversal in the direction of the sagittal plane motion as they extended the hip. The patients with a hesitation or reversal in motion had a greater loss in the range of motion of the hip during gait (p < 0.004) and a greater passive flexion contracture (p < 0.022) than those with a smooth pattern of hip motion. This alteration in the pattern of motion was interpreted as a mechanism to increase effective extension of the hip during stance through increased anterior pelvic tilt and lumbar lordosis. The patients who had osteoarthritis of the hip walked with significantly decreased external extension, adduction, and internal and external rotation moments (p < 0.008). The decreased extension moment was significantly correlated with an increased level of pain (R = 0.78; p < 0.001). This finding suggests that decreasing muscle forces (hip flexors) may be one mechanism used to adapt to pain.

  View details for Web of Science ID A1997YA23000020

  View details for PubMedID 9379275

• Gait biomechanics and the evolution of total joint replacement GAIT & POSTURE Andriacchi, T. P., Hurwitz, D. E. 1997; 5 (3): 256-264

  View details for Web of Science ID A1997XF37600011

• Patellofemoral design influences function following total knee arthroplasty JOURNAL OF ARTHROPLASTY Andriacchi, T. P., Yoder, D., Conley, A., Rosenberg, A., Sum, J., Galante, J. O. 1997; 12 (3): 243-249

  Abstract

  The functional influence of patellofemoral design was evaluated by testing two cohorts of patients with total knee arthroplasty while walking, climbing stairs, and rising from a chair. The two cohorts received one of two different designs of total knee arthroplasty. The designs differed primarily in the curvature of the femoral trochlea. These differences in curvature have been shown in in vitro studies to influence the tracking of the patella. One design had a smaller radius on the patellar flange, which caused the patella to articulate more anteriorly and distally than the second design, which had a larger radius in this region. The second design more closely replicated the curvature of the femoral trochlear anatomy. There was a significant functional difference during stairclimbing between the patient groups, whereas there was no difference during walking or chair rising. The group with the design that had nonanatomic tracking of the patella had a higher than normal moment tending to flex the knee (net quadriceps moment) during late stance phase. The increased net quadriceps moment during late stance was concurrent with an increased knee flexion. The abnormal function occurred when the patellar was tracking over the nonanatomic portion of the trochlea. Patients in the group with the anatomic trochlea did not have abnormal function. These results suggest a relationship between a nonanatomic trochlea and abnormal function during stair-climbing.

  View details for Web of Science ID A1997WU68800002

  View details for PubMedID 9113537

• Tractive forces during rolling motion of the knee: Implications for wear in total knee replacement JOURNAL OF BIOMECHANICS Wimmer, M. A., Andriacchi, T. P. 1997; 30 (2): 131-137

  Abstract

  Wear at the polyethylene tibial plateau in total knee arthroplasty (TKR) is one of the primary concerns with these devices. The artificial bearing of a TKR has to sustain large forces while allowing the mobility for normal motion, typically, rolling, gliding and rotation. The tractive forces during the rolling motion at the knee joint were analyzed to determine which factors cause these forces to increase in TKR. The implications of these tractive forces to polyethylene wear were considered. Traction forces were calculated using a model of the knee to evaluate the effect of variations in the coefficient of friction, gait characteristics, antagonistic muscle contraction and patellofemoral mechanics. The model was limited to the sagittal plane motion of the femur on the tibia. The input for the model was the shape of the articulating surface, coefficient of friction, contact path, muscle anatomy and gait kinetics common to patients with a total knee replacement. The generation of tractive forces on the tibial polyethylene plateau was highly dependent on the static and dynamic coefficient of friction between the femur and the tibia. A peak tractive force of approximately 0.4 body weight was calculated with a peak normal force of 3.3 body weight. Tractive rolling occurred during most of stance phase when the static coefficient was 0.2. Alterations in gait patterns had a substantial effect on the generation of tractive forces at the knee joint. When an abnormal gait pattern (often seen following TKR) was input to the model the posteriorly directed tractive force on the tibial surface was reduced. It was also found that variations in muscle contractions associated with antagonistic muscle activity as well as the angle of pull of the patellar tendon affected the magnitude of tractive forces. The results of the study suggest that there are feasible conditions following total knee replacement which can lead to tractive forces during rolling motion at the tibiofemoral articulation that should be considered in the analysis of factors leading to polyethylene damage in total knee replacement.

  View details for Web of Science ID A1997WC30400005

  View details for PubMedID 9001933

• Functional adaptations in patients with ACL-deficient knees. Exercise and sport sciences reviews Hurwitz, D. E., Andriacchi, T. P., Bush-Joseph, C. A., Bach, B. R. 1997; 25: 1-20

  View details for PubMedID 9213086

• Altered load history affects periprosthetic bone loss following cementless total hip arthroplasty JOURNAL OF ORTHOPAEDIC RESEARCH Bryan, J. M., Sumner, D. R., Hurwitz, D. E., TOMPKINS, G. S., Andriacchi, T. P., Galante, J. O. 1996; 14 (5): 762-768

  Abstract

  Dual energy x-ray absorptiometry was used to measure periprosthetic, distal femoral, and proximal tibial bone mass in the affected and contralateral limbs of eight patients 10 years after unilateral total hip arthroplasty with a cementless, porous-coated titanium alloy femoral stem. Gait analyses to assess the presence of asymmetries in loading of the lower extremities were also performed 10 years postoperatively. The patients had excellent clinical results and no other significant lower extremity pathology. On the basis of comparison of the affected and unaffected proximal femora, bone loss adjacent to the proximal medial aspect of the femoral stem was determined to be 34% (p < 0.001). However, the patients also had 16% less bone in the ipsilateral proximal tibia (p = 0.003) and 15% less bone in the ipsilateral femur 3 cm distal to the prosthesis (p = 0.007) compared with the contralateral limb. When normalized to the asymmetry in tibial bone mineral content, the estimated proximal medial periprosthetic bone loss was still statistically significant, but the magnitude was reduced from 34 to 17% (p = 0.009). The gait analyses indicated that several measures that influence the loads at the hip and knee joints were reduced in the involved limb compared with the contralateral limb. Furthermore, the bilateral difference in the vertical component of the external force acting on the proximal tibia was correlated with the bilateral difference in tibial bone mineral content (r = 0.80, p = 0.02). These data suggest that two mechanical factors, the local stress-shielding effect of the prosthesis and the global effect of decreased loading of the limb, can both make significant contributions to periprosthetic bone loss. It is apparent that the magnitude of the periprosthetic bone loss related to stress-shielding has been overestimated by as much as 50% in retrospective studies.

  View details for Web of Science ID A1996VP97200012

  View details for PubMedID 8893770

• Adaptation to differential loading: Comparison of growth-related changes in cross-sectional properties of the human femur and humerus BONE Sumner, D. R., Andriacchi, T. P. 1996; 19 (2): 121-126

  Abstract

  Changes in long bone cross-sectional geometry during growth can be influenced by biological and mechanical factors. Here, we assess relationships between cross-sectional geometric properties and length of the human humerus and femur during postnatal growth to test the hypothesis that loading history plays an important role in the development of adult bone morphology. A skeletal sample including 83 paired humeri and femora from individuals between birth and age 30 was examined. Midshaft cross-sectional geometric properties were determined based on computed tomographic scans and the two bones were compared by examining growth trajectories and scaling relationships between the cross-sectional properties and bone length. The growth trajectories for both bones were similar in many respects and showed that increase in length ceased by age 20, whereas increase in cross-sectional properties continued into the third decade of life. When compared to bone length, the cross-sectional geometric properties of the femur and humerus were similar early in postnatal life, but increased at a greater rate in the femur particularly during the first decade of life, leading to divergent adult morphologies. A beam model was developed to predict maximum midshaft strains in each bone as a function of age. The moment acting on the femur was estimated from an analysis of gait in children and the moment acting on the humerus was chosen so that the magnitude of the maximum midshaft strains in the two bones was equivalent in adulthood. With this model, the maximum midshaft strains for the femur were predicted to be higher than for the humerus during the first decade of life. These data support the concept that load history plays an important role in accretion of bone mass during postnatal growth.

  View details for Web of Science ID A1996VB74000007

  View details for PubMedID 8853855

• Functional analysis of cemented medial unicompartmental knee arthroplasty JOURNAL OF ARTHROPLASTY Chassin, E. P., MIKOSZ, R. P., Andriacchi, T. P., Rosenberg, A. G. 1996; 11 (5): 553-559

  Abstract

  Gait analysis was used to study patients who underwent cemented medial unicompartmental knee arthroplasty (UKA) for medial compartment degenerative knee disease. All had excellent clinical function of the operated knee, with minimal involvement of other joints. Ten patients met the inclusion criteria for this study. Gait findings from this study group, as well as those from a similar cohort of patients who had undergone total knee arthroplasty (TKA), were compared with those for a group of normal patients. A greater percentage of patients (7 of 10) following UKA maintained the normal biphasic flexion/extension moment pattern about the knee or demonstrated a quadriceps overuse pattern, when compared with similar groups following TKA. In addition, the adduction moment in patients following UKA was significantly larger than in patients following TKA. The postoperative limb alignment correlated with the peak adduction moment recorded during the patient's gait analysis. The postoperative alignment may explain the differences in the adduction moment between the UKA and TKA patients, as there tended to be residual varus in the UKA population. The results of this study imply that preservation of the anterior cruciate ligament during UKA allows patients to maintain normal quadriceps mechanics, and that residual varus alignment subjects a medial UKA to higher loads.

  View details for Web of Science ID A1996VF21000011

  View details for PubMedID 8872575

• Lower limb alignment and foot angle are related to stance phase knee adduction in normal subjects: A critical analysis of the reliability of gait analysis data JOURNAL OF ORTHOPAEDIC RESEARCH Andrews, M., Noyes, F. R., Hewett, T. E., Andriacchi, T. P. 1996; 14 (2): 289-295

  Abstract

  Anatomic and mechanical factors that affect loading in the knee joint can contribute to pathologic changes seen at the knee in degenerative joint disease and should be considered in treatment planning. The objectives of this study were to quantify the relationships between the alignment of the bones of the lower extremity, foot progression angle, and knee adduction moment, and to determine the reliability of our gait measurements. Gait analysis and complete radiographic evaluation of the lower extremity were performed on 11 healthy subjects. The gait measurements were recorded with an optoelectronic digitizer and a multi-component force plate. The subjects who had radiographic measurements indicative of varus alignment of the lower extremity had statistically higher peaks in knee adduction moment in early stance. Conversely, those with valgus alignment of the lower extremity had statistically lower peaks in knee adduction moment in early stance. The subjects who had a large toe-out angle and low ankle inversion moment peaks in late stance had significantly lower peaks in knee adduction moment in late stance. These significant (low to moderate) correlations suggest that the limbs with more valgus alignment and those with a toe-out gait exhibited a reduced peak adduction moment at the knee. To verify the reproducibility of the data, gait analysis testing was performed on each lower limb on 2 separate days for each subject. Analysis of variance showed that there was no significant difference between test limbs or test days for each subject. Our results suggest that the alignment of the lower limb and the foot progression angle, which can be readily measured in a clinical setting, can serve as predictors of knee joint loading in healthy individuals. These findings may have important implications for both surgical and nonsurgical treatment of abnormalities of the knee joint.

  View details for Web of Science ID A1996UK21800017

  View details for PubMedID 8648508

• Knee hyperextension gait abnormalities in unstable knees - Recognition and preoperative gait retraining AMERICAN JOURNAL OF SPORTS MEDICINE Noyes, F. R., Dunworth, L. A., Andriacchi, T. P., Andrews, M., Hewett, T. E. 1996; 24 (1): 35-45

  Abstract

  Five patients with symptomatic knee hyperextension thrusting patterns due to posterolateral ligament complex injury underwent gait analysis before and after a gait retraining program. Patients were trained to avoid knee hyperextension by 1) walking with their knees slightly flexed throughout stance, 2) maintaining ankle dorsiflexion in early stance, and 3) maintaining an erect trunk-hip attitude during stance. Kinematic and kinetic measurements were obtained using automated gait analysis. Four of the five patients significantly reduced hyperextension at the knee and abnormal motion patterns at the hip and ankle. Patients showed increases in knee flexion throughout stance conversions of knee flexion-extension moments to more normal biphasic patterns with a 79% decrease in extension moments at terminal extension, and a 22% decrease in knee adduction moments. Posttraining values also showed a 30% decrease in the calculated medial tibiofemoral loads (P < 0.05). At the hip, there were significant decreases in abduction and adduction moments (36% and 18%, respectively, P < 0.01). Ankle plantar flexion motion decreased significantly by 42% (P < 0.01). Gait retraining can alter the biomechanics of hip, knee, and ankle function to approximately normal levels, and therefore is recommended before ligament reconstruction because abnormal knee motions, if resumed postoperatively, can stretch soft tissue reconstructions.

  View details for Web of Science ID A1996TR33800007

  View details for PubMedID 8638751

• CHARACTERIZATION OF GAIT PARAMETERS IN ADULT-ONSET MYOTONIC-DYSTROPHY - ABNORMAL HIP MOTION ARCHIVES OF PHYSICAL MEDICINE AND REHABILITATION WRIGHT, R. B., Yoder, D. M., Costa, J. L., Andriacchi, T. P. 1995; 76 (1): 33-38

  Abstract

  The gait of five patients with myotonic dystrophy was analyzed using light-emitting diodes and a force plate. When compared with the gait of control subjects, that of myotonics suggested weakness of the tibialis anterior and triceps surae muscles. Although the myotonics showed no evidence of lower-extremity myotonia (delayed muscle relaxation following contraction), or of weakness of the hip or knee musculature, all had striking abnormalities in their hip motion. In contrast to the smooth and consistent extension of the hip throughout stance phase observed during gait in control subjects, the hips of myotonics oscillated irregularly as they progressed through stance phase extension, with considerable variation between legs and during successive strides. Excessive use of hip musculature in an attempt to control the oscillatory hip motion may contribute to the chronic fatigue associated with myotonic dystrophy.

  View details for Web of Science ID A1995QB19700005

  View details for PubMedID 7811171

• DYNAMICS OF KNEE MALALIGNMENT ORTHOPEDIC CLINICS OF NORTH AMERICA Andriacchi, T. P. 1994; 25 (3): 395-403

  Abstract

  The dynamics of malalignment are based on the combination of the static limb alignment and the dynamics of loading at the knee during walking and other activities of daily living. Dynamic loading at the knee can be influenced by subconscious control of limb position such as foot placement, active muscle contraction, passive soft-tissue stability, as well as the speed of walking. The loads that are generated during these dynamic activities are substantially greater than the loads that can be generated during static postures. Therefore, limb alignment based on static radiographic measurements provides one component to the complete analysis of the factors influencing loading at the knee joint. Loading at the knee joint is an important consideration in the progression of degenerative processes at the knee, as well as in the planning and selection of certain treatment modalities. Dynamic malalignment that occurs during activities such as gait should be considered in evaluating the progression of disease processes as well as the selection of appropriate treatment modalities.

  View details for Web of Science ID A1994NX07100005

  View details for PubMedID 8028883

• CHONDROCYTE CELLS RESPOND MECHANICALLY TO COMPRESSIVE LOADS JOURNAL OF ORTHOPAEDIC RESEARCH Freeman, P. M., Natarajan, R. N., Kimura, J. H., Andriacchi, T. P. 1994; 12 (3): 311-320

  Abstract

  Many studies have illustrated the effect of mechanical loading on articular cartilage and the corresponding changes in chondrocyte metabolism, yet the mechanism through which the cells respond to loading still is unclear. The purpose of this study was to evaluate the change in shape of chondrocytes under a statically applied uniaxial compressive load. Isolated chondrocytes from rat chondrosarcoma were embedded in 2% agarose gel. Strains of 5, 10, and 15% were applied, and images of the cell were recorded from initial loading to equilibrium (15 minutes). A finite-element model was used to model the experimental setup and to estimate the mechanical properties of the chondrocyte at equilibrium. The transient behavior of the composite in the experiment was analyzed with use of a standard linear viscoelastic model. We found that all cells decreased in cross-sectional area under each of the applied compressive strains. In the finite-element model, the elasticity of the chondrocyte was similar to that of the surrounding agarose gel (4.0 kPa) and had a Poisson's ratio of 0.4. Viscoelastic analysis showed that the chondrocytes contributed a significant viscoelastic component to the behavior of the composite in comparison with the agarose gel alone. If a decrease in cell volume proportional to the decrease in cross-sectional area is assumed, the decrease observed was greater than would be predicted by a passive cellular response due to an equivalent osmotic pressure. This indicates that the chondrocyte may be altering its intracellular composition by cellular processes in response to mechanical loading.

  View details for Web of Science ID A1994NQ51700002

  View details for PubMedID 8207584

• THE INFLUENCE OF LOAD KNOWLEDGE ON LIFTING TECHNIQUE ERGONOMICS Butler, D., Andersson, B. J., TRAFIMOW, J., Schipplein, O. D., Andriacchi, T. P. 1993; 36 (12): 1489-1493

  Abstract

  The purpose of this study was to analyse the influence of load knowledge on lifting technique. Ten men lifted a box containing either no weight or weights of 150, 250 or 300 N with and without knowledge of what was inside the box. The kinetics and kinematics of the lift were analysed using a force plate, an optoelectronic motion analysis system, and a rigid body link model. At 0 N lifting, the unknown load resulted in a jerk-like motion and a significantly increased peak L5-S1 flexion-extension moment. At 150 N there was also a significant increase in the speed of trunk extension with unknown weights, but the L5-S1 moment remained unchanged. At higher load levels there were only minor differences between lifting techniques when knowing and not knowing the load. We conclude that lifts are approached assuming a certain weight, and that when the assumption is wrong and the load lighter than anticipated lifting is performed with a 'jerking' motion, creating unnecessary loads on the lower back.

  View details for Web of Science ID A1993MK99800004

  View details for PubMedID 8287855

• Functional analysis of pre and post-knee surgery: total knee arthroplasty and ACL reconstruction. Journal of biomechanical engineering Andriacchi, T. P. 1993; 115 (4B): 575-581

  Abstract

  This paper examines the biomechanics of total knee arthroplasty as a treatment for arthritis and anterior cruciate ligament (ACL) reconstruction for repair of torn anterior cruciate ligaments of the knee. These are two of the most frequent reconstructive procedures for the knee joint. Functional testing of patients while performing various activities of daily living was used to study the relationship between the intrinsic biomechanics of the knee and function. The results of the study of patients following total knee replacement demonstrated a dynamic interaction between the posterior cruciate ligament and quadriceps function during stairclimbing. The study of patients with ACL-deficient knees demonstrated that loss of the anterior cruciate ligament can cause the avoidance of quadriceps contraction during activities when the knee is near full extension. Other studies demonstrated a relationship between tibiofemoral joint mechanics and patellofemoral mechanics. In addition, the importance of combined ligamentous laxity with higher than normal adduction moments during gait was examined in relationship to progressive degenerative changes to the medial compartment of the knee. In summary, functional testing such as gait analysis has proven to be an important basic research tool as well as extremely effective for clinical testing of new procedures and devices.

  View details for PubMedID 8302044

• STEM CURVATURE AND LOAD ANGLE INFLUENCE THE INITIAL RELATIVE BONE-IMPLANT MOTION OF CEMENTLESS FEMORAL STEMS JOURNAL OF ORTHOPAEDIC RESEARCH Berzins, A., Sumner, D. R., Andriacchi, T. P., Galante, J. O. 1993; 11 (5): 758-769

  Abstract

  A 6 df measurement system was used to investigate the initial relative bone-implant motion of two types of cementless total hip replacement femoral components-a straight stem and a curved stem. Five pairs of fresh frozen femurs from human cadavers were tested with loads applied to the femoral head at angles characteristic of level walking, stair-climbing, and rising from a chair. The most important findings were that (a) the resultant proximal translations were twice as high with the straight stem as with the curved stem at load angles encountered in stair-climbing and rising from a chair, (b) both stem types had more motion at load angles encountered in stair-climbing and rising from a chair than in level walking, with the increases ranging from 3 to 14-fold, (c) there was as much as 66-fold more motion distally than proximally, and (d) the amount of interface motion varied by 5-fold between the medial and lateral surfaces of the distal part of the implant because of the combined effects of translation and rotation. The amount of initial bone-implant motion of the femoral component was found to be particularly sensitive to off-axis loading; this suggests that stair-climbing and rising from a chair should be avoided in the early postoperative period when a cementless porous-coated femoral stem has been used.

  View details for Web of Science ID A1993ME48600017

  View details for PubMedID 8410476

• EFFECT OF PIROXICAM ON GAIT IN PATIENTS WITH OSTEOARTHRITIS OF THE KNEE ARTHRITIS AND RHEUMATISM Schnitzer, T. J., Popovich, J. M., Andersson, G. B., Andriacchi, T. P. 1993; 36 (9): 1207-1213

  Abstract

  To determine whether the use of a nonsteroidal antiinflammatory drug (NSAID) in patients with painful osteoarthritis (OA) of the knee would result in alterations in specific biomechanical parameters of gait.Eighteen patients with symptomatic knee OA and varus knee deformity underwent initial clinical evaluation for pain and activities of daily living, and assessment of parameters of gait utilizing a well-described computerized system. All patients were then treated with piroxicam at 20 mg once daily, and clinical and gait analyses were repeated after 4 weeks.Fifteen of the 18 patients studied had a significant increase in the knee adduction moment after treatment. In the group as a whole there was a significant increase in knee adduction moment (mean percent body weight times height [%BWTH] 4.11 pretreatment versus 4.57 after 4 weeks of treatment; P < 0.01) and maximum quadriceps moment (mean %BWTH 2.13 pretreatment, 2.62 posttreatment; P < 0.01), as well as changes in other gait parameters that might be expected to be altered as a result of relief of pain. Sixteen of 18 patients experienced symptomatic relief, with a significant reduction in pain in the group as a whole after 4 weeks (P < 0.001).NSAID treatment in patients with knee OA results in a reduction in symptomatic pain and an increase in loading of the knee. Whether the increased loading is due to the analgesic effects of the treatment is unknown, but if so, the development of agents capable of relieving pain while reducing loads at the knee may be desirable.

  View details for Web of Science ID A1993MB21100004

  View details for PubMedID 8216414

• FUNCTIONAL TESTING IN THE ANTERIOR CRUCIATE LIGAMENT-DEFICIENT KNEE CLINICAL ORTHOPAEDICS AND RELATED RESEARCH Andriacchi, T. P., BIRAC, D. 1993: 40-47

  Abstract

  Functional testing of patients with anterior cruciate ligament (ACL) deficient knees and normal subjects during stressful activities such as running to a cut and running to a stop and during activities common to daily life, such as walking, stair climbing, and jogging, is presented. Analysis focused on the application of these tests to treatment planning and clinical evaluation. Functional testing during stressful activities indicates that some patients with ACL-deficient knees have higher than normal net hamstring moments during the early phase of these activities. These results suggest dynamic muscular substitution using the hamstrings in patients with chronic ACL-deficient knees. Patients tested during less stressful activities, such as walking and stair climbing, also demonstrated substantial differences from ACL-intact subjects. The majority of patients tended to reduce the net quadriceps moment when the knee was near full extension. Approximately 75% of the patients who were ACL-deficient developed this type of adaptation, which appears to be a subconscious method of avoiding the net anterior pull of the quadriceps mechanism when the knee is near full extension. Functional testing of the ACL-deficient knee provides meaningful information that cannot be obtained by simpler clinical tests. This information can be extremely useful in the selection and evaluation of patients with certain treatment modalities, since it seems to be directly related to some patients' ability to functionally adapt to the loss of the ACL.

  View details for Web of Science ID A1993KW03600006

  View details for PubMedID 8458153

• THE ANTERIOR CRUCIATE LIGAMENT-DEFICIENT KNEE WITH VARUS ALIGNMENT - AN ANALYSIS OF GAIT ADAPTATIONS AND DYNAMIC JOINT LOADINGS AMERICAN JOURNAL OF SPORTS MEDICINE Noyes, F. R., Schipplein, O. D., Andriacchi, T. P., Saddemi, S. R., Weise, M. 1992; 20 (6): 707-716

  Abstract

  Thirty-two patients with an ACL-deficient knee and lower limb varus alignment and 16 healthy controls were analyzed during level walking using a force-plate and optoelectronic system. The forces and moments of the lower limb and knee joint were measured and knee joint loads and ligament tensile forces were calculated using a mathematical model. The majority of patients (20 of 32) had an abnormally high adduction moment at the affected knee. The adduction moment showed a statistically significant correlation to high medial tibiofemoral compartment loads and high lateral soft tissue forces, but not to the degree of varus alignment on standing roentgenograms. Fifteen of 32 knees had abnormally high lateral soft tissue forces. We interpreted these gait findings as indicative of a medial shift in the center of maximal joint pressure and an increase in lateral soft tissue forces to achieve coronal plane stability. Further, there is the likelihood of separation of the lateral tibiofemoral joint and "condylar lift-off" during periods of the stance phase. If this occurs, all of the load-bearing forces would shift to the medial tibiofemoral joint and relatively large tensile forces would occur in the lateral soft tissue restraints. The flexion moment, as related to the quadriceps muscle force, was significantly lower than the control knees in 40% of the involved knees, and the extension moment, as related to the hamstring muscle force, was significantly higher in 50% of the involved knees. We interpret this finding as a gait adaptation tending to diminish quadriceps muscle activity and enhance hamstring muscle activity to provide dynamic anteroposterior stability of the knee joint. The fundamental assumption of this paper is that any combination of conditions leading to higher medial joint forces is associated with factors leading to more rapid degeneration of the medial compartment in patients with ACL deficiency, varus deformity, and lax lateral ligaments.

  View details for Web of Science ID A1992JY69700012

  View details for PubMedID 1456365

• FORCE DISPLACEMENT CHARACTERISTICS OF THE POSTERIOR CRUCIATE LIGAMENT AMERICAN JOURNAL OF SPORTS MEDICINE Bach, B. R., DALUGA, D. J., MIKOSZ, R., Andriacchi, T. P., Seidl, R. 1992; 20 (1): 67-72

  Abstract

  The percent force changes in the posterior cruciate ligament were calculated using a previously validated computerized knee model after the femoral insertion sites were varied 2.5 and 5.0 mm in an anterior, posterior distal, anterior distal, and posterior distal direction. The tibial insertion sites were also varied 2.5 and 5.0 mm in the medial, lateral, proximal, and distal directions. Percent force changes were measured over a range of 0 degree to 90 degrees. These insertion sites simulated potential surgical placement errors. Results of this study demonstrated that the greatest percent force changes in the posterior cruciate ligament were at full extension. The greatest absolute percent force change between 0 degree and 90 degrees of flexion was with a femoral insertion of the posterior cruciate ligament placed 5 mm anterior to its normal attachment site, which resulted in a 39% change in the posterior cruciate ligament force. Distal femoral site attachment had the least effect (10% at 5.0 mm). Alterations at the tibial attachment site were less sensitive than on the femur; the greatest absolute percent force changes occurred with medial and lateral attachment sites (14% and 15%, respectively, at 5.0 mm). A minimal amount of percent force changes were seen between 45 degrees and 75 degrees of knee flexion in all positions tested for both tibial and femoral attachment sites. This model suggests that, like the anterior cruciate ligament, the force in the posterior cruciate ligament is also sensitive to attachment site position. As in anterior cruciate ligament studies, the femoral attachment site was found to be more sensitive.(ABSTRACT TRUNCATED AT 250 WORDS)

  View details for Web of Science ID A1992HB59300016

  View details for PubMedID 1554076

• A relationship between stem orientation and function following total hip arthroplasty. journal of arthroplasty Hodge, W. A., Andriacchi, T. P., Galante, J. O. 1991; 6 (3): 229-235

  Abstract

  A retrospective gait analysis of patients with cemented Charnley-Mueller total hip arthroplasties was conducted to determine if functional differences exist between patients with femoral stems placed in varus and valgus orientations. Twenty patients and ten normals were studied using gait analysis to quantify joint motion and moments during level walking. In addition, a radiographic analysis of stem placement and mechanics of the reconstructed hip was performed on the total hip patients. All patients selected for the study had excellent clinical results on the basis of a score of 95 or better on the Harris hip rating form. The patients were divided into two subgroupings on the basis of stem orientation. A valgus group was defined as having a valgus stem orientation relative to the femoral shaft, with the femoral head-shaft offset shortened by 5 mm or greater compared to the contralateral unoperated hip, while the varus group was defined on the basis of having a varus stem orientation relative to the femoral shaft, with the femoral head-shaft offset restored to normal or greater than normal. A difference in gait was found between the varus and valgus patient groupings. The varus group had abnormal gait characteristics in the range of hip motion, the flexion-extension moments at the hip, and stride length. The patients in the valgus group had statistically normal gait. The differences in the gait characteristics were interpreted as an attempt to alter forces on the hip joint for patients in the varus group. These alterations were possibly an early indication of a subtle adaptation in patients with varus-placed femoral stems since, historically, a greater percentage of the patients in this configuration, retrospectively, go on to mechanical failures.(ABSTRACT TRUNCATED AT 250 WORDS)

  View details for PubMedID 1940928

• INTERACTION BETWEEN ACTIVE AND PASSIVE KNEE STABILIZERS DURING LEVELWALKING JOURNAL OF ORTHOPAEDIC RESEARCH Schipplein, O. D., Andriacchi, T. P. 1991; 9 (1): 113-119

  Abstract

  The gait of normal subjects and patients with varus deformities at the knee was studied by analyzing the interaction between the dynamic (muscular) and passive (ligamentous) restraints affecting lateral stability of the knee. A statistically determinant model predicted that the midstance-phase adducting moment during normal gait would cause lateral knee joint opening if either antagonistic muscle force and/or pretension in the lateral soft tissues were not present at the knee. The patient group tended to compensate for a high midstance-phase adducting moment by walking with a style of gait that demanded more muscle force (greater flexion-extension moments). This walking style reduced the chance of lateral joint opening. It can be speculated that this style of gait would help to maintain equilibrium at the knee. The higher muscle force would aid in resisting the adducting moment, keeping the joint closed laterally and thus increasing the stability of the knee.

  View details for Web of Science ID A1991EP31500013

  View details for PubMedID 1984041

• Gait adaptations by patients who have a deficient anterior cruciate ligament. journal of bone and joint surgery. American volume BERCHUCK, M., Andriacchi, T. P., Bach, B. R., Reider, B. 1990; 72 (6): 871-877

  Abstract

  Sixteen patients who had unilateral deficiency of the anterior cruciate ligament and ten healthy control subjects were analyzed during level walking, jogging, and ascending and descending stairs. Kinematic and kinetic findings for the right and left hips, knees, and ankles of all of the patients and control subjects were recorded during each activity. Substantial differences from normal function were observed for both limbs of the patients during level walking and during jogging. The magnitude of the maximum moment that tended to flex the knee was reduced the most (140 per cent) during level walking. It was reduced less (30 per cent) during jogging, it was not changed while the patient descended stairs, and it was slightly increased while he or she ascended stairs. The reduction in the magnitude of the flexion moment about the knee was interpreted as the patient's effort to reduce or avoid contraction of the quadriceps. Reduction of the flexion moment reduces any contraction of the quadriceps because there must be a mechanical balance between the external moment (due to body weight and the weight and inertia of the segment of the limb) that tends to flex the knee and an internal moment (generated by contraction of the quadriceps) that tends to extend the knee. This so-called quadriceps-avoidance gait was related to the angle of flexion of the knee when the maximum flexion moment occurred during each activity. This angle of flexion was 20 degrees during walking, 40 degrees during jogging, and approximately 60 degrees during stair-climbing.(ABSTRACT TRUNCATED AT 250 WORDS)

  View details for PubMedID 2365720

• GAIT ADAPTATIONS BY PATIENTS WHO HAVE A DEFICIENT ANTERIOR CRUCIATE LIGAMENT JOURNAL OF BONE AND JOINT SURGERY-AMERICAN VOLUME BERCHUCK, M., Andriacchi, T. P., Bach, B. R., Reider, B. 1990; 72A (6): 871-877

  View details for Web of Science ID A1990DP46900012

• THE INFLUENCE OF WALKING MECHANICS AND TIME ON THE RESULTS OF PROXIMAL TIBIAL OSTEOTOMY JOURNAL OF BONE AND JOINT SURGERY-AMERICAN VOLUME Wang, J. W., Kuo, K. N., Andriacchi, T. P., Galante, J. O. 1990; 72A (6): 905-909

  Abstract

  The current study describes the influence of the passage of time on the original findings. The mechanisms used by some patients to reduce loading at the knee (adduction moment) also were analyzed. We evaluated the gait of twenty-seven patients (thirty-two knees) who had had a proximal tibial osteotomy for a varus gonarthrosis. Twenty-four patients (twenty-eight knees) returned for follow-up at three to 8.9 years after the osteotomy. This is a follow-up to our original study (Prodromos et al.), which described a relationship between the magnitude of the adduction moment at the knee during walking and the outcome of proximal tibial osteotomy. The patients were divided into low and high adduction-moment groups on the basis of the magnitude of the adduction moment at the knee as measured preoperatively during walking. All fourteen patients in the low adduction-moment group and nine of the fourteen patients in the high adduction-moment group had a good or excellent result. The varus deformity recurred in ten patients in the high adduction-moment group and in three patients in the low adduction-moment group. All of the results degenerated over time. The adaptive mechanism that was used to lower the adduction moment during gait included shortening the stride and toeing-out. The significant correlation between the magnitudes of the inversion moment at the ankle and the adduction moment at the knee suggested that the toe-out gait reduced the adduction moment at the knee.(ABSTRACT TRUNCATED AT 250 WORDS)

  View details for Web of Science ID A1990DP46900017

• A functional and radiographic analysis of the total condylar knee arthroplasty. journal of arthroplasty BRUGIONI, D. J., Andriacchi, T. P., Galante, J. O. 1990; 5 (2): 173-180

  Abstract

  Twenty-one knees in 14 patients were studied during walking, in clinical follow-up, and radiographically. The purpose was to examine the relationship between dynamic loading at the knee joint during level walking in the early postoperative period (1-2 years) and longer-term (4 years) prosthetic performance. Joint kinematics and kinetics were measured while patients were walking in the laboratory. The results were compared with an age-matched control group of healthy normal subjects. Patients were analyzed when grouped according to original diagnoses of rheumatoid or osteoarthritis. After total knee arthroplasty, patients with rheumatoid arthritis walked with a significantly lower magnitude peak adduction moment (force tending to thrust the knee into varus) about the knee than patients with osteoarthritis. The osteoarthritic group had an increased varus axial alignment when compared to the rheumatoid group. There was a strong correlation between postoperative varus alignment and the magnitude of the adduction moment. These results suggest that dynamic loading at the knee is greatly affected by static alignment of the joints in patients with total knee arthroplasty. In spite of the lower adduction moment during level walking and its associated effects on lower compressive loads at the knee, the patients with rheumatoid arthritis had a significantly higher radiolucency index. Thus, it appears that quality of bone stock may be a more important factor in determining prosthetic loosening than dynamic loading at the knee joint following total knee arthroplasty.

  View details for PubMedID 2358816

• RELATIONSHIP BETWEEN MOMENTS AT THE L5-S1 LEVEL, HIP AND KNEE-JOINT WHEN LIFTING JOURNAL OF BIOMECHANICS Schipplein, O. D., TRAFIMOW, J. H., Andersson, G. B., Andriacchi, T. P. 1990; 23 (9): 907-912

  Abstract

  A study was performed to determine the influence of load magnitude on the self selected technique of lifting. Specifically, it was hypothesized that with heavier weights a tendency would occur to lift more with the back and less with the legs. Flexion-extension moments at the L5/S1 level, hip and knee joints were calculated for subjects when lifting boxes weighing from 50 to 250 N. Lifts were performed using a freestyle technique at normal speed. The moment profiles (moment plotted vs time) were analyzed kinematically and as a function of the weight lifted. The kinematics of the lift changed as the weight increased. The moment at the L5/S1 level increased with increasing weight, however, the corresponding knee moment decreased. Thus, an inverse relationship was found between the moment at the L5/S1 level and the knee joint moment. An increase in weight lifted was also associated with an increase in the angular velocity at the knee while lifting. Apparently with heavier weights there is a tendency to extend the knees earlier during the lift than with lighter weights, confirming our hypothesis. This explains the reduced knee moment. Our findings lead to the hypothesis that quadriceps muscle strength limits the subjects' ability to lift with their knees flexed.

  View details for Web of Science ID A1990DW84300004

  View details for PubMedID 2211735

• DYNAMICS OF PATHOLOGICAL MOTION - APPLIED TO THE ANTERIOR CRUCIATE DEFICIENT KNEE JOURNAL OF BIOMECHANICS Andriacchi, T. P. 1990; 23: 99-105

  Abstract

  The analysis of the dynamics of pathological motion can provide new and meaningful knowledge about musculoskeletal disorders. The application of the study of pathological ambulation to the analyses of clinical problems is analyzed and discussed. The importance of the selection of appropriate measurement protocols and variable selection is illustrated using an example of the evaluation of patients with an anterior cruciate deficient knee. In particular, the importance of the joint moment as a measure of normal and pathological ambulation is described. An example is provided from a study based on the analysis of 16 patients with unilateral anterior cruciate deficiency. Patients were studied during walking, jogging and ascending and descending stairs. The results are used to demonstrate the importance of testing activities of the knee (e.g. walking, jogging, stair-climbing) that stress the knees during different ranges of motion in order to differentiate functional adaptation associated with the anterior cruciate deficient knee. Results demonstrate that functional abnormalities occur during low stress activities such as level walking. Further, it appears that the functional adaptation occurring during these activities is associated with the anterior force generated on the tibia when the quadriceps contract and the knee is near full extension. It appears that locomotion patterns are reprogrammed to produce an adaptive gait in the majority of patients with anterior cruciate deficient knees.

  View details for Web of Science ID A1990EV30400010

  View details for PubMedID 2081748

• Evaluation of surgical procedures and/or joint implants with gait analysis. Instructional course lectures Andriacchi, T. P. 1990; 39: 343-350

  View details for PubMedID 2186121

• THE INFLUENCE OF CHAIR HEIGHT ON LOWER-LIMB MECHANICS DURING RISING JOURNAL OF ORTHOPAEDIC RESEARCH Rodosky, M. W., Andriacchi, T. P., Andersson, G. B. 1989; 7 (2): 266-271

  Abstract

  The mechanics of the lower limb were analyzed in young, adult normal subjects when rising from a seated position. Limb mechanics were described in terms of flexion-extension motion and moments at the hip, knee and ankle while rising from four seat heights corresponding to 65, 80, 100, and 115% of the subject's knee joint height. The results indicate that the maximum moment tending to flex the hip joint was higher than that occurring at the knee or ankle. The magnitude of the maximum flexion moment at the hip was not substantially influenced by chair height, changing by less than 12% between the highest and lowest chair heights. Conversely, the maximum knee flexion moments were found to be highly dependent on chair height and nearly doubled from the highest to the lowest position. The magnitude of the moments at the ankle did not change with chair height and were significantly lower than the magnitude of the moments found during normal walking. The magnitude of motion and moments at the hip were greater during chair-rising than during stair-climbing or walking. The range of motion required at the knee for the lower chair heights was also greater than was reported during stair-climbing studies. Thus, the combination of moments in joint angles during chair-rising are unique among common activities of daily living and should be considered in chair selection as well as in the guidelines for prosthetic devices.

  View details for Web of Science ID A1989T300200014

  View details for PubMedID 2918425

• COMPUTED TOMOGRAPHIC MEASUREMENT OF CORTICAL BONE GEOMETRY JOURNAL OF BIOMECHANICS Sumner, D. R., Olson, C. L., Freeman, P. M., LOBICK, J. J., Andriacchi, T. P. 1989; 22 (6-7): 649-653

  Abstract

  In this study digital images of bone cross-sections obtained by computed tomography were analyzed with an automated outlining method. It was shown that unbiased cross-sectional geometric measurements of cortical bone could be obtained if the periosteal and endosteal surfaces were defined at separate thresholds. Use of different threshold levels for these two surfaces resulted in errors of 2.6% for periosteal diameters, 7.4% for endosteal diameters and 7.3% for cortical area. If incorrect thresholds were used, cortical thickness measurements can have errors as high as 30%. In addition, simulated variation in medullary fat content did not affect measurement of medullary dimensions.

  View details for Web of Science ID A1989CA09200015

  View details for PubMedID 2808447

• RELATIONSHIP BETWEEN DYNAMIC DEFORMITIES AND JOINT MOMENTS IN CHILDREN WITH CEREBRAL-PALSY JOURNAL OF PEDIATRIC ORTHOPAEDICS Lai, K. A., Kuo, K. N., Andriacchi, T. P. 1988; 8 (6): 690-695

  Abstract

  A relationship between dynamic flexion-extension motion ranges during walking and the magnitude of flexion and extension moments was analyzed for 38 ambulatory children with spastic cerebral palsy. Moments tending to flex the hip and the knee were more than a factor of two times greater than those occurring during normal gait. At the knee, the magnitude of the moments was related to the amount of flexion deformity, whereas at the hip there was no correlation between moment magnitude and extension motion range. The maximum dorsiflexion and plantarflexion ankle moments were of less than normal value in all deformity groupings. An understanding of the longterm influence of these abnormal moments on the terms of the progression or stabilization of the dynamic deformities during walking is an important step toward improving our understanding of and, potentially, our ability to treat patients with cerebral palsy.

  View details for Web of Science ID A1988Q655600012

  View details for PubMedID 3192697

• PATELLAR COMPONENT FAILURE IN CEMENTLESS TOTAL KNEE ARTHROPLASTY CLINICAL ORTHOPAEDICS AND RELATED RESEARCH Rosenberg, A. G., Andriacchi, T. P., Barden, R., Galante, J. O. 1988: 106-114

  Abstract

  One hundred twenty-two total knee arthroplasties were performed with porous ingrowth fixation of the patellar component between February 1984 and February 1987. Twelve subsequently have experienced fatigue fracture of the patellar component at the peg-plate junction. All fractured patellar components demonstrated excellent ingrowth and fixation of the porous titanium fiber mesh-peg surfaces with no ingrowth into the porous plate underlying the polyethylene patellar surface. While the initial group of 122 arthroplasties was only slightly greater than one-third male, the preponderance of patellar fractures was in males (ten of 12). Patients with patellar component failure were on average younger and heavier and had a greater range of knee motion than the index group. The average time from implantation to recognition of fracture was 24 months. Biomechanical analysis of the force system about a domed patella demonstrated that loading of the patellofemoral joint results in eccentric loading of the dome surface. Peg fixation not accompanied by fixation of the overlying plate allows these high eccentric forces to load the peg-plate junction in shear with consequent fatigue at the peg-plate junction. These results indicate that the shear forces are sufficiently high to warrant caution in the use of peg-plate systems in which peg ingrowth without plate ingrowth occurs.(ABSTRACT TRUNCATED AT 250 WORDS)

  View details for Web of Science ID A1988R039800012

  View details for PubMedID 3180561

• INFLUENCE OF DYNAMIC FACTORS AND EXTERNAL LOADS ON THE MOMENT AT THE LUMBAR SPINE IN LIFTING SPINE BUSECK, M., Schipplein, O. D., Andersson, G. B., Andriacchi, T. P. 1988; 13 (8): 918-921

  Abstract

  Flexion-extension moments occurring at the L5-S1 level of the spine were calculated when subjects lifted a box weighing from 50 to 250 N. Lifting was performed at normal and fast speed, and the lifts were performed using a freestyle and a leglifting technique. The peak moment increased linearly with increasing load. The moment/load relationship was significantly influenced by lifting speed, and a higher moment occurred at each load level when lifting fast. Lifting speed was reduced when the external load was increased, particularly when the load was 150 N and higher. Moments when lifting using the leglifting technique were lower than when lifting freestyle.

  View details for Web of Science ID A1988Q612900009

  View details for PubMedID 3187716

• Biomechanics and gait analysis in total knee replacement. Orthopaedic review Andriacchi, T. P. 1988; 17 (5): 470-473

  Abstract

  A primary goal of total knee replacement has been the relief of pain. As new implant designs evolve and other improvements take place, we must broaden our goals to include increased longevity and an improvement in patient function, especially among younger patients. There is a relationship between the longevity of the implant and patient function, since function determines loads on the joint and the motion of the joint. In addition, ultimate breakdown of the prosthesis depends upon these same loads. This paper will first discuss the relationship between function and some of the intrinsic mechanics of the knee joint, and then the relationship between function and mechanics and the longevity of the implant. It is based on an analysis of patients with a variety of differently designed total knee replacements that replicate, to a greater or lesser degree, the anatomy of the knee joint. Some of the implants sacrifice both anterior and posterior cruciates, and some retain both.

  View details for PubMedID 3174215

• MODEL ANALYSIS OF FACTORS INFLUENCING THE PREDICTION OF MUSCLE FORCES AT THE KNEE JOURNAL OF ORTHOPAEDIC RESEARCH MIKOSZ, R. P., Andriacchi, T. P., Andersson, G. B. 1988; 6 (2): 205-214

  Abstract

  A three-dimensional stochastic mathematical muscle model of the knee joint has been developed and applied to a study in which the influence of both mechanical and physiological factors were examined in relation to the prediction of muscular forces about the joint. The model includes a representation of the proximal portion of the tibia and distal portion of the femur along with a mathematical expression of the patellar mechanism and 13 muscles crossing the knee joint. The model accounts for the rolling and gliding movement of the tibial-femoral articulation. The computational technique involves equilibrating three components of external moments at the knee joint to the internal moments generated by muscular forces and soft tissue. The variables contained in the moment equilibrium equation are randomly chosen based on the choice of the tibial-femoral contact point. The randomness of the variables, reflected in the final solution, defines a stochastic process in the context of the present model. Studies with the model indicated that a very important mechanical aspect of the model was the capability to simulate the moving contact point between the tibia and femur. The moving contact point increased the mechanical advantage of the quadriceps muscles by 50%, which corresponded to in vivo EMG measurements. Muscle force predictions during normal gait have shown the capability of the model to determine the presence of synergistic and antagonistic muscle action.

  View details for Web of Science ID A1988M409700006

  View details for PubMedID 3278080

• INFLUENCE OF DYNAMIC FACTORS ON THE LUMBAR SPINE MOMENT IN LIFTING ERGONOMICS BUSHJOSEPH, C., SCHIPPLEIN, O., Andersson, G. B., Andriacchi, T. P. 1988; 31 (2): 211-216

  View details for Web of Science ID A1988M956800005

  View details for PubMedID 3371330

• DYNAMIC ANALYSES OF LIFTING 7TH CONGRESS OF THE INTERNATIONAL SOC OF ELECTROPHYSICAL KINESIOLOGY Andersson, G. B., Schipplein, O. D., TRAFIMOW, J. H., Andriacchi, T. P. ELSEVIER SCIENCE PUBL B V. 1988: 437–440

  View details for Web of Science ID A1988BR83A00084

• Retention of the posterior cruciate in total knee arthroplasty. journal of arthroplasty Andriacchi, T. P., Galante, J. O. 1988; 3: S13-9

  Abstract

  Retention of the posterior cruciate ligament in total knee arthroplasty is discussed in biomechanical and clinical terms and the implications for design, kinematics, function, and prosthesis longevity considered. The specific roles of passive range of motion, femoral rollback, stresses on the implant-bone-prosthesis cement system, and wear are examined. The authors argue that the posterior cruciate ligament improves passive range of motion, the mechanical efficiency of the knee musculature and thus improved stairclimbing efficiency, reduces stress at the cement-bone-implant interfaces, and has little or no impact on the polyethylene wear problems.

  View details for PubMedID 3199135

• INTERACTION BETWEEN INTRINSIC KNEE MECHANICS AND THE KNEE EXTENSOR MECHANISM JOURNAL OF ORTHOPAEDIC RESEARCH Draganich, L. F., Andriacchi, T. P., Andersson, G. B. 1987; 5 (4): 539-547

  Abstract

  The ability of the quadriceps muscles to extend the knee was studied relative to the intrinsic mechanical features of the knee joint. The quadriceps mechanical efficiency changed by nearly 50% between 0 and 90 degrees of knee flexion. The peak efficiency occurred at approximately 20 degrees of knee flexion. The mechanical efficiency of the quadriceps was dependent on the movement of the net anteroposterior (AP) tibiofemoral contact center of pressure, the change in patellar ligament angle, and the change in the quadriceps-to-ligament force transfer ratio. The average net AP tibiofemoral contact center of pressure moved posteriorly on the tibial plateau as the knee flexed from 0 to 90 degrees. The excision of both cruciate ligaments reversed the posteriorly directed movement of the net AP tibiofemoral contact center of pressure at flexion angles from 60 to 90 degrees, resulting in a reduction in extension moment.

  View details for Web of Science ID A1987L138700008

  View details for PubMedID 3681528

• ANALYSIS OF THE MULLER ANTEROLATERAL FEMOROTIBIAL LIGAMENT RECONSTRUCTION USING A COMPUTERIZED KNEE MODEL AMERICAN JOURNAL OF SPORTS MEDICINE Gibson, M., MIKOSZ, R., Reider, B., Andriacchi, T. 1986; 14 (5): 371-375

  Abstract

  Iliotibial tract tenodesis has been described by Müller as part of the surgical treatment for anterolateral rotatory instability in the ACL deficient knee. The aim of this study was to use a previously described and validated computer model of the knee to calculate the effectiveness of Müller's extraarticular anterolateral femorotibial ligament (ALFTL) graft as a substitute for the ACL or as an adjunct to an intraarticular ACL reconstruction in the ACL deficient knee. This effectiveness was tested by simulating the application of a torque sufficient to create 15 degrees of internal rotation or 5 mm of anterior displacement of the tibia on the femur at 0 degrees, 15 degrees, and 30 degrees of knee flexion. The effects of moving the graft's proximal fixation point 1 cm superior, inferior, and anterior to the current surgical attachment site were examined to determine the amount of permissible surgical error in graft placement. The model predicts that the ALFTL is a useful restraint to internal rotation when it is performed with or without an intraarticular ACL reconstruction. The ALFTL graft took up greater amounts of tension and became more effective at increasing angles of knee flexion. Placement of the ALFTL graft 1 cm anterior to the current surgical attachment site decreases the vector component that lies perpendicular to the long axis of the tibia and consequently reduces resistance to internal rotation. The ALFTL graft at any attachment site was ineffective in resisting pure anterior displacement between 0 degrees and 30 degrees.

  View details for Web of Science ID A1986E558400004

  View details for PubMedID 3777312

• Knee biomechanics and total knee replacement. journal of arthroplasty Andriacchi, T. P., STANWYCK, T. S., Galante, J. O. 1986; 1 (3): 211-219

  Abstract

  The biomechanics of the knee joint provide an important basis for the rationale in the design and selection of appropriate total knee arthroplasty. This article examines knee biomechanics in terms of patient function, prosthesis design, cruciate ligament retention, alignment, and fixation of the tibial component. While design and surgical technique for total knee replacement progress, a better understanding of the characteristics of joint loading, stress distribution, and the biologic response of bone to stress will provide the potential to improve both function and implant longevity.

  View details for PubMedID 3559597

• Factors influencing walking and stairclimbing following unicompartmental knee arthroplasty. journal of arthroplasty Weinstein, J. N., Andriacchi, T. P., Galante, J. 1986; 1 (2): 109-115

  Abstract

  The authors quantitatively evaluated the relationship between component placement, limb alignment, and function following unicompartmental knee replacement surgery. It was found that anatomic alignment, prosthetic positioning, and prosthetic design influence the patients' ability to walk and climb stairs. There was wide variation in the placement of the tibial and femoral component among patients. The placement of the femoral component corresponded directly to function during stairclimbing and level walking. Anterior malpositioning of the femoral component resulted in reduced ability to climb stairs. The tibial component position varied primarily in varus-valgus position. Varus-valgus alignment in the frontal plane correlated directly with the magnitude of the adduction moment during level walking. A varus alignment produced a twofold increase in the magnitude of the adduction moment at the knee during walking. Given the potential advantages of the unicompartmental knee, improved precision in component placement should improve the long-term results of hemiarthroplasty knee surgery.

  View details for PubMedID 3559579

• A relationship between gait and clinical changes following high tibial osteotomy. journal of bone and joint surgery. American volume PRODROMOS, C. C., Andriacchi, T. P., Galante, J. O. 1985; 67 (8): 1188-1194

  Abstract

  We studied the cases of twenty-one patients with high tibial osteotomy in order to determine the relationship between knee-joint loading during gait and clinical outcome. The patients were tested before surgery, one year after surgery, and again at an average of 3.2 years after surgery. An age-matched group of fifteen control subjects was also studied. The results of this study indicate that certain characteristics of preoperative walking are associated with postoperative clinical results. In particular, the moment tending to adduct the knee joint during walking preoperatively was predictive of postoperative clinical results. The patients were classified into a high adduction-moment group and a low adduction-moment group according to the magnitude of the knee-adduction moment. The adduction moment was reduced in both groups after high tibial osteotomy. However, the average postoperative adduction moments in the low adduction-moment group were still significantly lower than those in the high adduction-moment group. The two groups were indistinguishable on the basis of preoperative knee score, initial varus deformity, immediate postoperative correction, age, and weight. However, at an average 3.2-year follow-up, patients with low preoperative adduction moments had substantially better clinical results than did patients with high adduction moments. The low adduction-moment group had 100 per cent excellent or good clinical results, while only 50 per cent of the patients in the high adduction-moment group had an excellent or good result. Furthermore, there was a significant recurrence of varus deformity in the patients in the high adduction-moment group.(ABSTRACT TRUNCATED AT 250 WORDS)

  View details for PubMedID 4055843

• A RELATIONSHIP BETWEEN GAIT AND CLINICAL CHANGES FOLLOWING HIGH TIBIAL OSTEOTOMY JOURNAL OF BONE AND JOINT SURGERY-AMERICAN VOLUME PRODROMOS, C. C., Andriacchi, T. P., Galante, J. O. 1985; 67A (8): 1188-1194

  View details for Web of Science ID A1985ATF8600007

• A study of factors influencing muscle activity about the knee joint. Journal of orthopaedic research Andriacchi, T. P., Andersson, G. B., Ortengren, R., MIKOSZ, R. P. 1984; 1 (3): 266-275

  Abstract

  Several factors influencing the myoelectric activity of muscles surrounding the knee joint were studied using fine-wire monopolar electrodes. The muscles studied included the vastus lateralis, vastus intermedius, rectus femoris, vastus medialis, gracilis, sartorius, biceps femoris, semimembranosus, semitendinosus, tensor fasciae latae, medial head of the gastrocnemius, and lateral head of the gastrocnemius. Muscle activity was measured in response to unidirectional loads tending to flex and extend the knee, and to combined loads of flexion-adduction, flexion-abduction, extension-adduction, and extension-abduction. Results indicate that the individual muscle responses are dependent upon the direction, magnitude, and combination of external moments, as well as on the flexion angle of the knee joint. Muscle response appeared to be influenced by certain intrinsic mechanical characteristics of the knee joint that tend to change the moment arms of the muscles as the knee moves. For example, the substantial changes in quadriceps myoelectric activity with knee flexion, with constant load applied, can be related to the movement of the tibial-femoral contact changing the lever arm of the quadriceps mechanism. This study indicates that the mechanics of the knee joint must be taken into consideration while attempting to interpret or predict the load response of muscles crossing the knee joint.

  View details for PubMedID 6481510

• MODEL STUDIES OF THE STIFFNESS CHARACTERISTICS OF THE HUMAN KNEE-JOINT JOURNAL OF BIOMECHANICS Andriacchi, T. P., MIKOSZ, R. P., HAMPTON, S. J., Galante, J. O. 1983; 16 (1): 23-29

  Abstract

  A three-dimensional mathematical model of the ligamentous knee joint has been developed and applied to studies of the mechanical response of the knee joint. The model includes a representation of the bony portion of the knee including the proximal tibia, distal femur, soft tissue structure and the contacting surfaces of the medial and lateral condyles. The bony portions of the model are represented by rigid bodies while the soft tissue structures are represented by spring and beam type elements. The model employs the direct stiffness approach from structural mechanics and uses an incremental linearization procedure for the geometric and material non-linearities. Studies with the model indicate that the geometric type non-linearities contribute to the overall non-linear response of the knee joint. It was also found that the load-displacement response of the knee is highly dependent on constraints to coupled degrees of freedom. This finding may be an important consideration when interpreting the results of standard laxity tests at the knee, which by their nature may impose constraints to motion.

  View details for Web of Science ID A1983QE15900003

  View details for PubMedID 6833307

• THE INFLUENCE OF FEMORAL STEM THICKNESS AND IMPLANTATION TECHNIQUE ON THE STRENGTH OF THE BONE-CEMENT BOND ACTA ORTHOPAEDICA SCANDINAVICA SAVINO, A. W., Andersson, G. B., Andriacchi, T. P., Hampton, S., Galante, J. O. 1982; 53 (1): 23-27

  Abstract

  The influence of stem thickness, stem orientation, and insertion pressure on the strength of a prosthesis-cement-bone system was studied in vitro. Three types of prostheses were used with thick and thin stems, allowing for thick or thin cement envelopes. They were implanted with different stem orientations, and with and without a distal femoral cement plug. They were then loaded in a testing machine until a discontinuity of the load deflection curve occurred. The main factor determining the failure load was the presence of the distal plug. In specimens with plugs the main load at failure was 6.5 N, in specimens without a plug it was 4.8 N (P greater than 0.05). The most stable combination was the thick stem with a thin cement envelope placed in valgus or neutral orientation, and implanted with a distal cement plug. It was concluded that when no plug was present failure occurred at the bone-cement interface; when a plug was present it occurred at the prosthesis-cement interface.

  View details for Web of Science ID A1982NE69200005

  View details for PubMedID 7064678

• A TECHNIQUE FOR EMBEDDING STRAIN-GAUGES WITHIN CURING BONE-CEMENT JOURNAL OF BIOMECHANICS Draganich, L. F., Andriacchi, T. P., Galante, J. O. 1982; 15 (10): 789-790

  Abstract

  A technique has been described to embed strain gages within curing bone cement. Both open faced and encapsulated strain gages were employed. Using a simple cantilever beam in bending test, the experimentally measured strains were linear over the range of bending strains applied and in good agreement with the calculated theoretical values.

  View details for Web of Science ID A1982PW23900008

  View details for PubMedID 7153232

• THE INFLUENCE OF TOTAL KNEE-REPLACEMENT DESIGN ON WALKING AND STAIR-CLIMBING JOURNAL OF BONE AND JOINT SURGERY-AMERICAN VOLUME Andriacchi, T. P., Galante, J. O., FERMIER, R. W. 1982; 64 (9): 1328-1335

  View details for Web of Science ID A1982PU52100008

  View details for PubMedID 7142241

• THE INFLUENCE OF EARLY WEIGHT-BEARING ON EXPERIMENTAL TOTAL HIP ARTHROPLASTIES IN DOGS CLINICAL ORTHOPAEDICS AND RELATED RESEARCH Gitelis, S., Chen, P. Q., Andersson, G. B., Galante, J. O., ROSTOKER, W., Andriacchi, T. P. 1982: 291-302

  Abstract

  The bone-cement interface is an area of concern in the long-term fixation of endoprostheses. The effect of early weight-bearing on the interface has been discussed as an important parameter influencing the characteristics of the interface. In this study, a total hip arthroplasty was performed in two groups of six dogs each. One group was allowed immediate weight-bearing, while in the other, a knee disarticulation amputation was done to prevent weight-bearing. Three animals of each group were killed at three months and three of each group at six months, and a histological study of the interface was done. No morphologic difference was observed between weight-bearing and nonweight-bearing animals in the interface area. Endosteal bone remodeling occurred regardless of weight-bearing stresses. A fibrous membrane was found between the cement and the endosteal surface of the femur, and membrane thickness was similar in all animals. The membrane between the cement and acetabular bone, however, was consistently thicker. Quantitative studies revealed increased femoral cortical bone resorption in the nonweight-bearing animals.

  View details for Web of Science ID A1982PF82300041

  View details for PubMedID 7105589

• CORRELATIONS BETWEEN CHANGES IN GAIT AND IN CLINICAL STATUS AFTER KNEE ARTHROPLASTY ACTA ORTHOPAEDICA SCANDINAVICA Andersson, G. B., Andriacchi, T. P., Galante, J. O. 1981; 52 (5): 569-573

  Abstract

  Twenty-six knee arthroplastics in 22 subjects were studied clinically and in a gait laboratory before and on one or more occasions after surgery. The purpose was to identify changes in gait characteristics and relate them to changes in the clinical situation of the patients. The gait patterns of the patients changed following surgery mainly with respect to their time-distance characteristics; stride length, cadence, time of swing, and time of support. Positive correlations were noted between these gait changes and the patient's pain, his limp, and his walking distance. It is concluded that the information obtained in sophisticated gait laboratory is of limited value to the surgeon in his clinical assessment.

  View details for Web of Science ID A1981MT38600015

  View details for PubMedID 7331794

• CHANGES IN THE GAIT PATTERNS OF GROWING CHILDREN JOURNAL OF BONE AND JOINT SURGERY-AMERICAN VOLUME Beck, R. J., Andriacchi, T. P., Kuo, K. N., FERMIER, R. W., Galante, J. O. 1981; 63 (9): 1452-1457

  Abstract

  We observed the gait patterns, including time and distance measurements and ground reaction forces, of fifty-one normal children. Thirty-three children were retested once at one, three, six, nine, or twelve months, over a two-year period, for a total of eighty-four gait observations. Time and distance measurements and foot-ground reaction force measurements were found to be dependent on walking speed and the age of the child. An increase in height with age was found to be the major factor in determining the changes in time and distance measurements with age. For example, we found that average stride length was 76 per cent of the child's height at a walking speed of 1.04 meters per second regardless of the child's age. In contrast, the three components of foot-ground reaction force (vertical, lateral, and forward directions) were observed to vary with age up to five years even when normalized. After the age of five years an adult pattern of ground reaction force emerged. In addition, we found that walking patterns of children who were more than found years old did not vary when retested within a three-month period. However, for children less than four years old, measurements were found to change due to growth during the three-month period to retesting. Similar changes due to growth were found in children more than four years old who were tested at intervals more than three months apart. This important finding may be clinically useful in the study of the effects of treatment.

  View details for Web of Science ID A1981MY01200012

  View details for PubMedID 7320036

• A STUDY OF LOWER-LIMB MECHANICS DURING STAIR-CLIMBING JOURNAL OF BONE AND JOINT SURGERY-AMERICAN VOLUME Andriacchi, T. P., Andersson, G. B., FERMIER, R. W., Stern, D., Galante, J. O. 1980; 62 (5): 749-757

  Abstract

  The motions, forces, and moments at the major joints of the lower limbs of ten men ascending and descending stairs were analyzed using an optoelectronic system, a force-plate, and electromyography. The mean values for the maximum sagittalplane motions of the hip, knee, and ankle were 42, 88, and 27 degrees, respectively. The mean maximum net flexion-extension moments were: at the hip, 123.9 newton-meters going up and 112.5 newton-meters going down stairs; at the knee, 57.1 newton-meters going up and 146.6 newton-meters going down stairs; and at the ankle, 137.2 newton-meters going up and 107.5 newton-meters going down stairs. When going up and down stairs large moments are present about weight-bearing joints, but descending movements produce the largest moments. The magnitudes of these moments are considerably higher than those produced during level walking.

  View details for Web of Science ID A1980KB41600008

  View details for PubMedID 7391098

• INFLUENCE OF HIP RECONSTRUCTION ON GAIT SURGICAL FORUM Hodge, W. A., Andriacchi, T. P., Galante, J. O. 1980; 31: 517-519

  View details for Web of Science ID A1980KU26000229

• ELECTRONIC MEASUREMENT OF INSTANTANEOUS FOOT-FLOOR CONTACT PATTERNS DURING GAIT JOURNAL OF BIOMECHANICS Draganich, L. F., Andriacchi, T. P., Strongwater, A. M., Galante, J. O. 1980; 13 (10): 875-880

  View details for Web of Science ID A1980KS08300007

  View details for PubMedID 7462261

• 3-DIMENSIONAL STRESS-ANALYSIS OF THE FEMORAL STEM OF A TOTAL HIP-PROSTHESIS JOURNAL OF BIOMECHANICS HAMPTON, S. J., Andriacchi, T. P., Galante, J. O. 1980; 13 (5): 443-448

  View details for Web of Science ID A1980JU60000006

  View details for PubMedID 7400172

• 3-DIMENSIONAL COORDINATE DATA-PROCESSING IN HUMAN MOTION ANALYSIS JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME Andriacchi, T. P., HAMPTON, S. J., Schultz, A. B., Galante, J. O. 1979; 101 (4): 279-283

  View details for Web of Science ID A1979HT57800009

• PROTHESIS CEMENT ENVELOPE IN FEMORAL COMPONENT TOTAL HIPS SURGICAL FORUM SAVINO, A. W., Andersson, G. B., Andriacchi, T. P., Galante, J. O. 1978; 29: 556-557

  Abstract

  Loading tests showed wide stem-thin cement envelope systems in valgus orientation placed with distal plug to be significantly more stable at higher loads. Narrow stem-thick cement envelope systems in varus without plug were unstable within a marginal factor of safety for cyclic loading. Four cement failures occurred within the thin stem-thick cement system on the upper lateral aspect of the prosthesis cement envelope.

  View details for Web of Science ID A1978GA40500232

  View details for PubMedID 401259

• WALKING SPEED AS A BASIS FOR NORMAL AND ABNORMAL GAIT MEASUREMENTS JOURNAL OF BIOMECHANICS Andriacchi, T. P., OGLE, J. A., Galante, J. O. 1977; 10 (4): 261-268

  View details for Web of Science ID A1977DG31500006

  View details for PubMedID 858732

• MILWAUKEE BRACE CORRECTION OF IDIOPATHIC SCOLIOSIS - BIOMECHANICAL ANALYSIS AND A RESTROSPECTIVE STUDY JOURNAL OF BONE AND JOINT SURGERY-AMERICAN VOLUME Andriacchi, T. P., Schultz, A. B., Belytschko, T. B., DeWald, R. L. 1976; 58 (6): 806-815

  Abstract

  We analyzed the biomechanics of Milwaukee brace treatment of idiopathic scoliotic patients through simulation in five computer-constructed model spines. The contributions to correction of each component of the brace were examined in these model spines, and some of the mechanical principles that determine the outcome of brace treatment were studied. The validity of the stimulation findings was then tested by a retrospective analysis. Simulation was used to predict the outcome of milwaukee brace treatment in sixty-eight patients. In 81 per cent of these patients, the actual outcome agreed with the prediction. The study suggests that careful adherence to mechanical principles in the use of a Milwaukee brace will result in successful treatment of more patients.

  View details for Web of Science ID A1976CF34100011

  View details for PubMedID 956227

• STRESS ANALYSIS OF FEMORAL STEM IN TOTAL HIP PROSTHESES JOURNAL OF BONE AND JOINT SURGERY-AMERICAN VOLUME Andriacchi, T. P., Galante, J. O., Belytschko, T. B., Hampton, S. 1976; 58 (5): 618-624

  Abstract

  A two-dimensional stress analysis was used to study the effects of some of the factors leading to early fatigue failure of the femoral stem in total hip prostheses. The results show that loss of proximal stem support at the level of the calcar femorale will result in stem stress levels which can lead to fatigue failure. In addition, the role of body weight and range of cyclic stress fluctuation play an important role in fatigue life under conditions where the stem has lost proximal support. These results indicate that stem design could be improved by incorporating some means of ensuring adequate support at the calcar femoralre maximum tensile stresses are found to occur.

  View details for Web of Science ID A1976BZ29900006

  View details for PubMedID 932061

• MODEL FOR STUDIES OF MECHANICAL INTERACTIONS BETWEEN HUMAN SPINE AND RIB CAGE JOURNAL OF BIOMECHANICS Andriacchi, T., Schultz, A., Belytschko, T., Galante, J. 1974; 7 (6): 497-507

  View details for Web of Science ID A1974V200300004

  View details for PubMedID 4452675

• ANALOG STUDIES OF FORCES IN HUMAN SPINE - COMPUTATIONAL TECHNIQUES JOURNAL OF BIOMECHANICS Belytschko, T. B., Andriacchi, T. P., Schultz, A. B., Galante, J. O. 1973; 6 (4): 361-371

  View details for Web of Science ID A1973Q160700004

  View details for PubMedID 4732936

• ANALOG STUDIES OF FORCES IN HUMAN SPINE - MECHANICAL PROPERTIES AND MOTION SEGMENT BEHAVIOR JOURNAL OF BIOMECHANICS Schultz, A. B., Belytschko, T. B., Andriacchi, T. P., Galante, J. O. 1973; 6 (4): 373-383

  View details for Web of Science ID A1973Q160700005

  View details for PubMedID 4732937

• A study of geometrical relationships in scoliotic spines. Journal of biomechanics Schultz, A. B., LAROCCA, H., Galante, J. O., Andriacchi, T. P. 1972; 5 (4): 409-420

  View details for PubMedID 4666200

• STUDY OF GEOMETRICAL RELATIONSHIPS IN SCOLIOTIC SPINES JOURNAL OF BIOMECHANICS Schultz, A. B., Galante, J. O., Andriacchi, T. P., LAROCCA, H. 1972; 5 (4): 409-?

  View details for Web of Science ID A1972M900000009