How predictions of medial and lateral knee contact forces during walking, stair ascent and stair descent are affected by tibiofemoral alignment and contact locations in patients with knee osteoarthritis: a musculoskeletal modeling analysis

The onset and progression of knee osteoarthritis and the cartilage degenerative process are related, among biological and mechanical factors, to the knee contact forces of the medial compartment, where the major percentage of the total contact force is transferred. Musculoskeletal modeling represents a state-of-the-art tool to predict knee contact forces, which are affected by two major geometric parameters: tibiofemoral alignment and contact point locations. Recent research show that medial contact force has a controversial level of correlation with tibiofemoral alignment and a marked correlation with contact points. However, there are limited and controversial data on osteoarthritis subjects, and few studies analyzing activities different from walking and without the inclusion of the geometric parameters. Therefore, the aim of this thesis is to evaluate how medial and lateral knee contact forces during walking, stair ascent and stair descent are affected by the inclusion of personalized tibiofemoral alignment and contact points in knee osteoarthritis patients, and to analyze the relationship between the knee contact forces and the geometric parameters. Fifty-one knee osteoarthritis patients participated in this study. Weight-bearing radiographs were acquired to measure tibiofemoral alignment and contact points by using in-house developed software. Motion capture data including 3D marker trajectories, ground reaction forces and EMG activities were recorded according to the established IORgait protocol. A validated full-body musculoskeletal model was used to calculate knee contact forces during the different motor activities by implementing an inverse-dynamics and static optimization workflow in OpenSim. We created four sets of models with increasing level of personalization in geometric parameters for each patient and performed the simulations of motion. To analyze the effect of geometric parameters, we evaluated statistically significant differences in knee contact forces among models across the activity cycles (statistical parametric mapping with non-parametric paired t-tests), and statistically significant differences among the force peaks (Mann-Whitney U-tests). To analyze the relationship between force peaks and geometric parameters, we performed a linear regression analysis (R, p). We found significant differences in knee contact forces among all models in most of the activity cycles during all motor activities. The largest difference was found between the tibiofemoral alignment and contact point personalized models, which could reach a 1.2 body-weight mean difference in the medial force. Almost all force peak distributions were found statistically significant different among models. Mild significant correlations were found between medial contact force and tibiofemoral alignment during stair descent only, while more marked correlations were found between medial contact forces and medial contact points during walking and stair descent (p < 0.05). Finally, an indirect model validation showed marked correlation between predicted muscle activations and recorded EMG activities. This study demonstrated the large impact of the geometric parameters, mostly contact points, on the knee contact forces during different motor activities via musculoskeletal modeling. There is a lateral shift of the knee loads when introducing the contact point personalization, which had more significant effect on the medial contact force than tibiofemoral alignment in knee osteoarthritis patients.