Prediction of Model Generated Patellofemoral Joint Contact Forces Using Principal Component Prediction and Reconstruction.

It is not currently possible to directly and noninvasively measure in vivo patellofemoral joint contact force during dynamic movement; therefore, indirect methods are required. Simple models may be inaccurate because patellofemoral contact forces vary for the same knee flexion angle, and the patellofemoral joint has substantial out-of-plane motion. More sophisticated models use 3-dimensional kinematics and kinetics coupled to a subject-specific anatomical model to predict contact forces; however, these models are time consuming and expensive. We applied a principal component analysis prediction and regression method to predict patellofemoral joint contact forces derived from a robust musculoskeletal model using exclusively optical motion capture kinematics (external approach), and with both patellofemoral and optical motion capture kinematics (internal approach). We tested this on a heterogeneous population of asymptomatic subjects (n = 8) during ground-level walking (n = 12). We developed equations that successfully capture subject-specific gait characteristics with the internal approach outperforming the external. These approaches were compared with a knee-flexion based model in literature (Brechter model). Both outperformed the Brechter model in interquartile range, limits of agreement, and the coefficient of determination. The equations generated by these approaches are less computationally demanding than a musculoskeletal model and may act as an effective tool in future rapid gait analysis and biofeedback applications.

Is discharge knee range of motion a useful and relevant clinical indicator after total knee replacement? Part 2.

OBJECTIVE: Knee range of motion (ROM) at discharge from acute care is used as a clinical indicator following total knee replacement (TKR) surgery. This study aimed to assess the clinical relevance of this indicator by determining whether discharge knee ROM predicts longer-term knee ROM and patient-reported knee pain and function. METHODS: A total of 176 TKR recipients were prospectively followed after discharge from acute care. Outcomes assessed included knee ROM and Oxford knee score post rehabilitation and 1 year post surgery. Discharge ROM and other patient factors were identified a priori as potential predictors in multiple linear regression modelling. RESULTS: A total of 133 (76%) and 141 (80%) patients were available for follow-up post rehabilitation [mean postoperative week 8.1 (SD 2.7)] and at 1 year [mean postoperative month 12.1 (SD 1.4)], respectively. Greater discharge knee flexion was a significant (P < 0.001) predictor of greater post-rehabilitation flexion but not 1-year knee flexion (P < 0.083). Better discharge knee extension was a significant predictor of better post-rehabilitation (P = 0.001) and 1-year knee extension (P = 0.013). Preoperative Oxford score and post-rehabilitation knee flexion independently predicted post-rehabilitation Oxford score, and gender predicted 1-year Oxford score. Discharge ROM did not significantly predict Oxford score in either model. CONCLUSION: The finding that early knee range predicts longer-term range provides clinical evidence favouring the relevance of discharge knee ROM as a clinical indicator. Although longer-term patient-reported knee pain and function were not directly associated with discharge knee ROM, they were associated with ROM when measured concurrently in the sub-acute phase. No causal effect has been demonstrated, but the findings suggest it may be important for physiotherapists to maximize range in the early and sub-acute periods.