Conceptual modeling of structural malalignments and ankle joint contact forces during walking

Background: Structural malalignments, such as talar malalignments and hindfoot varus, are hypothesized to contribute to early ankle joint degeneration by altering joint contact force (JCF). These malalignments, common in individuals with chronic ankle instability (CAI), can modify the articular geometry of the ankle joint, potentially leading to abnormal joint loading patterns. This study leverages musculoskeletal modeling and simulation to conceptualize the effects of increasing severity of these malalignments on ankle JCF during walking. Research question: Using a theoretical framework based on biomechanical principles, how do increasing talar malalignments and rearfoot varus, as seen in CAI patients, influence ankle JCF during walking? Methods: A conceptual musculoskeletal modeling approach was employed to simulate the effects of structural alterations on ankle JCF in uninjured individuals. Using an instrumented treadmill, musculoskeletal modeling was used to estimate the effects of increasing talar positional malalignments and/or rearfoot varus, both in isolation and in combination, on ankle JCF during the stance phase of walking. Variables included peak, impulse, and loading rates for compressive, posterior shear, and lateral shear JCF. Results: Anterior translation and internal rotation of the talus significantly increased lateral shear JCF, while an increase in rearfoot varus decreased lateral shear JCF (p < 0.01). However, combining modifications of the talus and rearfoot varus had no significant effects on ankle JCF. Significance: This conceptual analysis highlights the effectiveness of musculoskeletal modeling in providing theoretical insights into how CAI-related structural malalignments affect ankle joint loading during walking. Talar positional malalignments increase lateral shear loading, whereas rearfoot varus reduces lateral shear loading. The effects of these structural alterations on lateral shear JCF counterbalance each other, highlighting the need to consider other factors of CAI to more accurately reflect the ankle JCF in those with CAI.