Side‐Step Cutting Foot Biomechanics and Intrinsic Foot Muscle Sizes in People With Chronic Ankle Instability

INTRODUCTION: Lateral ankle sprains commonly occur during directional changes and often lead to chronic ankle instability (CAI) associated with altered movement patterns, muscle weakness and atrophy. This study aimed to compare foot joint biomechanics during cutting among individuals with CAI, copers, and uninjured controls and to explore the relationship between intrinsic foot muscle sizes and functional status. METHODS: . Groups were compared using ANOVA or Kruskal-Wallis tests, and continuous biomechanical data were analysed using statistical parametric or non-parametric mapping. Cross-sectional area and thickness of the abductor hallucis and flexor digitorum brevis were recorded using ultrasound imaging. Muscle sizes were explored using general linear models, and correlations with questionnaire scores and physical examination outcomes were calculated. RESULTS: Foot joint kinematics and kinetics did not significantly differ between the groups. Individuals with CAI exhibited lower peak posterior ground reaction force than controls (mean difference: -6.2% of body weight, 95% CI: -11.9 to -0.4, p = 0.03). Statistical parametric mapping revealed lower posterior ground reaction forces from 22% to 46% of stance in CAI versus controls (p < 0.05). Intrinsic foot muscle sizes showed weak, statistically significant negative correlations with perceived instability scores (ρ = -0.31 to -0.36) and self-reported function scores (ρ = -0.26 to -0.33). CONCLUSION: Despite pronounced sensory-perceptual impairments, individuals with CAI demonstrated few differences in foot joint biomechanics compared with copers and controls during a moderate-speed anticipated cutting task. Reduced braking forces may reflect altered deceleration strategies. These findings suggest the importance of assessing deceleration abilities in people with CAI and indicate a potential role of foot muscles in CAI-related functional outcomes. TRIAL REGISTRATION: ClinicalTrials.gov (NCT05815576).