Ankle joint contact forces and muscle contributions during walking differentiate chronic ankle instability from...

Chronic ankle instability (CAI) is associated with abnormal joint loading and an increased risk of early joint degeneration, yet the underlying biomechanical mechanisms remain unclear. It is unknown whether altered ankle loading reflects chronic effects of repeated ankle sprains rather than a single traumatic event, and how muscle forces contribute to these differences.

Ankle joint contact forces (JCF) and muscle contributions during walking were compared among 21 uninjured controls, 21 copers (individuals with a prior ankle sprain but no persistent symptoms), and 21 individuals with CAI. Participants completed treadmill gait analysis at a self-selected speed. Musculoskeletal modeling was used to estimate muscle contributions to tri-axial ankle JCF.

Individuals with CAI exhibited significantly lower compressive JCF compared with both uninjured controls and copers (p = 0.007), primarily due to reduced triceps surae force. Participants with CAI also demonstrated higher posteriorly directed shear JCF relative to controls and copers (p ≤ 0.008), driven mainly by increased tibialis anterior force during early stance. Additionally, individuals with CAI showed higher laterally directed shear JCF compared with uninjured controls, attributable to altered contributions from shank muscles and ground reaction forces (p ≤ 0.041).

Altered ankle joint loading during walking appears specific to CAI rather than a history of ankle sprain alone. Differences in muscle force contributions distinguish CAI from successful post-sprain adaptation and suggest that rehabilitation strategies targeting muscle coordination may help restore more coper-like joint loading patterns.