Dynamic Step-Down Tasks Reveal Altered Lower Limb Biomechanics in Chronic Ankle Instability.

BACKGROUND: Accurate knowledge about biomechanical alterations in chronic ankle instability (CAI) during dynamic movements may inform rehabilitation strategies. OBJECTIVE: To identify movement patterns associated with CAI injury during a step-down task. METHOD: Seventeen participants with CAI and 17 healthy controls performed a step-down task from heights of 20 and 40 cm. Lower limb joint angles, range of motion (ROM), moments, and power were measured. The one-dimensional statistical parametric mapping (SPM) test compared groups across the entire task (0%-100%). RESULTS: At 20 cm height, the CAI group exhibited greater hip abduction angles (0%-2%, p = 0.024 and 21%-77%, p = 0.014) but smaller hip abduction (7%-13%, 19%-20%, and 47%-64% (p < 0.05)), hip external rotation (8%-12% and p = 0.04), knee abduction (7%-30%, p = 0.001 and 49%-53%, p = 0.024), and ankle external rotation moments (7%-42% and p = 0.001). At 40 cm height, the CAI group showed greater hip abduction (44%-100% and p = 0.005), reduced ankle eversion (4%-12% and p = 0.012) angles, and smaller hip abduction, hip external rotation, knee abduction, ankle plantarflexion, and external rotation moments (all p < 0.05). No between-group differences were observed for the ROMs and power (p > 0.05). CONCLUSION: CAI individuals exhibited greater hip abduction, less ankle eversion, and smaller muscle moments, which are associated with an increased risk of injury. Rehabilitation should emphasize strengthening the hip muscles to mitigate the risk of injury.