Directional Kinetic Characteristics of Drop Landing for Patients with Functional Ankle Instability

This study aimed to investigate the kinetic characteristics, potential injury risk factors, and energy dissipation strategies of bilateral lower limbs during multidirectional drop landings in patients with unilateral functional ankle instability (FAI). Methods: Fifteen male patients with unilateral FAI participated in this study. Kinetic data were synchronously collected using a Vicon infrared motion capture system and a Kistler 3D force platform during single-leg drop landings performed in three directions (forward/oblique/side, FL/OL/SL) for both the unstable and stable limbs. A repeated-measures analysis of variance was conducted to compare the kinetic performance across directions and between sides. Results: Peak vertical ground reaction force (PvGRF), the time to PGRF in the vertical and lateral directions, the loading rate, and hip joint torques were affected by direction (p < 0.05). Hip torques at initial contact were significantly influenced by limb side (p < 0.05), and an interaction effect between direction and side was observed for ankle plantarflexion torques (p < 0.05). Specifically, the unstable limb ankle plantarflexion torques in FL and OL were lower than those in SL, while on the stable limb, plantarflexion torques in FL were lower than in OL and SL. Furthermore, plantarflexion torques were greater in the stable limb than in the unstable limb during FL and OL (p < 0.05). Conclusions: OL exerted higher medial ankle impact forces, while SL, which combines forward and lateral loading components, placed higher adaptive demands on the unstable ankle. FAI patients relied on compensatory strategies, with increased dependence on the stable limb for energy dissipation during drop landing movements.