Aberrant mechanical loading in knee osteoarthritis: model-based analysis of gait and stair negotiation

Four studies were conducted in this PhD aiming to evaluate knee joint loading assessed by calculating knee contact forces (KCF) using a musculoskeletal modeling workflow during common daily-living activities as walking and more demanding tasks, in individuals with varying levels of medial knee osteoarthritis (OA) severities. In study I, KCF were calculated and its relations with knee external knee adduction moments (KAM) and/or flexion moments (KFM) assessed during the stance phase of gait. Knee loading was evaluated in individuals with early medial knee OA, classified based on early joint degeneration on MRI and compared to individuals with established medial knee OA and healthy subjects. The effect of using an anatomical versus a functional axis of rotation (FAR) on KAM in healthy subjects and patients with knee OA was investigated in study II. In addition, this study reports KAM for models with FAR calculated using weight-bearing and non-weight-bearing motion. Study III calculates KCF and contact pressures during gait and step-up-and-over tasks in subjects with early knee OA and those with established knee OA compared to healthy subjects using a multi-body knee model with articular cartilage contact, 14 ligaments, and 6-DoF tibiofemoral and patellofemoral joints. Finally, study IV assessed trunk kinematics, KCF and knee contact pressures in individuals with medial knee OA during different stair negotiation strategies: step-over-step (SOS) at controlled speed, and also SOS at self-selected speed and step-by-step (SBS). This PhD contributed to, firstly, describe the importance of calculating the KCF in both medial and lateral knee compartments to better assess loading changes in individuals with varying levels of medial knee OA severities, especially those with early knee OA, during gait. The medial KCF provided a more sensitive metric to knee joint loading than external KAM or total KCF. Secondly, KAM was shown to be sensitive to the knee axis of rotation, indicating that differences between subject groups might be heavily dependent on the knee axis definition. Finally, different mechanisms used by these patients were identified during gait versus step/stair activities when compared to healthy subjects. Stair negotiation forced the use of compensatory mechanisms in patients with knee OA while gait did not