Effects of ankle angle changes on anterior talofibular ligament length and eversion strength in patients with ankle sprain

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Background Recurrent lateral ankle sprains (LAS) with chronic ankle instability (CAI) frequently results in damage to the anterior talofibular ligament (ATFL). Eversion muscle strength is crucial for prevention; however, its relationship with ATFL length, an indicator of ankle instability, remains unclear. Objective To investigate the relationship and compare ATFL length and eversion muscle strength between the non-CAI and CAI sides. Methods Twenty-five adults (50 feet; 12 males; 13 females) with unilateral CAI, voluntarily participated. ATFL length was measured using ultrasonography. Eversion muscle strength was assessed using a handheld dynamometer during maximum isometric contraction. The measurement position was taken with the ankle in two positions: neutral and 20° plantar flexion (P/F). Results ATFL length was significantly greater on the CAI side than on the non-CAI side in the P/F position (p < 0.05). The ankle eversion muscle strength was significantly lower on the CAI side than on the non-CAI side in the P/F position (p < 0.01). Only the CAI side in the P/F position showed a moderate negative correlation between ATFL length and eversion muscle strength (r = −0.45, p = 0.02). Conclusions Highlighting decreases in eversion muscle strength in the P/F position may be related to the increased ATFL length observed in CAI.