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Compressive knee joint contact force during walking is thought to be related to initiation and progression of knee osteoarthritis. However, joint loading is often evaluated with surrogate measures, like the external knee adduction moment, due to the complexity of computing joint contact forces. Statistical models have shown promising correlations between medial knee joint contact forces and knee adduction moments in particularly in individuals with knee osteoarthritis or after total knee replacements (R2 = 0.44–0.60). The purpose of this study was to evaluate how accurately model-based predictions of peak medial and lateral knee joint contact forces during walking could be estimated by linear mixed-effects models including joint moments for children and adolescents with and without valgus malalignment. Peak knee joint moments were strongly correlated (R2 > 0.85, p < 0.001) with both peak medial and lateral knee joint contact forces. The knee flexion and adduction moments were significant covariates in the models, strengthening the understanding of the statistical relationship between both moments and medial and lateral knee joint contact forces. In the future, these models could be used to evaluate peak knee joint contact forces from musculoskeletal simulations using peak joint moments from motion capture software, obviating the need for time-consuming musculoskeletal simulations.
Gait analysis as a clinical examination method has been increasingly used in recent years. In particular, the external knee adduction moment was often used as a surrogate measure for internal medial knee joint loading, e.g., in elderly individuals with medial knee osteoarthritis. Therefore, the knee adduction moment is also associated with the progression of knee osteoarthritis. Children and adolescents with valgus malalignment have been found to experience a reduced external knee adduction moment, but internal knee joint contact forces, particularly in the lateral compartment, were not previously studied.
First, medial and lateral knee joint contact forces were studied using muskulosceletal modeling in young individuals with and without valgus malalignment treated by guided growth. In addition, a systematic literature review was conducted to explore the relationship between external joint moments and internal joint contact forces. Finally, this relationship was investigated in children and adolescents with and without valgus malalignment. Furthermore, we examined whether statistical models could be determined to accurately predict internal knee joint contact forces by commonly used parameters from three-dimensional gait analysis, such as external knee joint moments.
It was found that guided growth normalized knee joint contact forces after treatment. In addition, the static radiographic mechanical axis angle correlated better after the treatment when the patients showed a typical limb alignment compared to the correlation before guided growth with the valgus malalignment due to compensating strategies during gait. Furthermore, the systematic review showed that the peak medial knee joint contact force was best predicted by the knee adduction moment and even better together with the knee flexion moment in the first half of stance. However, for the second half of stance of the medial knee joint contact force and the entire stance of the lateral knee joint contact force, only low correlations with knee adduction and/or flexion moment were found. Finally, statistical models could be determined with high accuracy for both medial and lateral knee joint contact force, for both peaks in the first and second half of stance, and for both study groups of children and adolescents with and without valgus malalignment by including knee adduction and flexion moment as predictors.
These results demonstrate the importance of examining not only the external knee adduction moment but also the knee flexion moment and, even better, the medial and lateral knee joint contact forces when evaluating knee joint loading. With these statistical models, clinicians can predict the medial and lateral knee joint contact forces without the need to perform musculoskeletal simulations and can therefore use standard three-dimensional gait analysis parameters such as knee adduction and flexion moment. This can improve guided growth treatment in children and adolescents with valgus malalignment with regard to implantation or explantation of the growth restricting plates or to rebound. Instrumented gait analysis could be particularly helpful in borderline cases, as kinematic compensation mechanisms during gait may play a role and the static radiograph alone does not provide information about dynamic joint loads.
Reduced external knee adduction moments in the second half of stance after total hip replacement have been reported in hip osteoarthritis patients. This reduction is thought to shift the load from the medial to the lateral knee compartment and as such increase the risk for knee osteoarthritis. The knee adduction moment is a surrogate for the load distribution between the medial and lateral compartments of the knee and not a valid measure for the tibiofemoral contact forces which are the result of externally applied forces and muscle forces. The purpose of this study was to investigate whether the distribution of the tibiofemoral contact forces over the knee compartments in unilateral hip osteoarthritis patients 1 year after receiving a primary total hip replacement differs from healthy controls. Musculoskeletal modeling on gait was performed in OpenSim using the detailed knee model of Lerner et al. (2015) for 19 patients as well as for 15 healthy controls of similar age. Knee adduction moments were calculated by the inverse dynamics analysis, medial and lateral tibiofemoral contact forces with the joint reaction force analysis. Moments and contact forces of patients and controls were compared using Statistical Parametric Mapping two-sample t-tests. Knee adduction moments and medial tibiofemoral contact forces of both the ipsi- and contralateral leg were not significantly different compared to healthy controls. The contralateral leg showed 14% higher medial tibiofemoral contact forces compared to the ipsilateral (operated) leg during the second half of stance. During the first half of stance, the lateral tibiofemoral contact force of the contralateral leg was 39% lower and the ratio 32% lower compared to healthy controls. In contrast, during the second half of stance the forces were significantly higher (39 and 26%, respectively) compared to healthy controls. The higher ratio indicates a changed distribution whereas the increased lateral tibiofemoral contact forces indicate a higher lateral knee joint loading in the contralateral leg in OA patients after total hip replacement (THR). Musculoskeletal modeling using a detailed knee model can be useful to detect differences in the load distribution between the medial and lateral knee compartment which cannot be verified with the knee adduction moment.