Peroneal muscle function compensates for the anterior talofibular ligament during static standing balance in patients with chronic ankle instability

The aim of this study is to clarify the factors that affect static standing balance and the relationship between the laxity of the anterior talofibular ligament and the thickness of the peroneal muscle.

The subjects were 25 females (age 19±1 years, BMI 21±2%), with 40 legs in the CON group and 10 legs in the CAI group. CAI groups were divided using the Cumberland ankle instability tool, with those scoring less than 25 points being classified as the CAI group and those scoring 25 points or more being classified as the CON group.

Ankle range of motion, muscle strength, leg-heel alignment, and medial longitudinal foot arch efficiency were measured. Using an ultrasound imaging device, the change in the length of the anterior talofibular ligament during the anterior drawer test was calculated. Static standing balance was assessed using the Y-Balance test.

Statistics were performed using unpaired t-tests to compare the two groups, multiple regression analysis to extract factors influencing Y-Balance, and Pearson correlation coefficients to calculate the relationship between Y-Balance and each factor.

There were no significant differences in anthropometric parameters between the two groups. Multiple regression analysis showed that the anterior Y-Balance distance was related to thin peroneal muscle thickness (R² = 0.50, p 0.001), and the posterior-lateral distance was related to muscle thickness (R² = 0.73, p 0.001). In the CON group, Y-Balance in all directions was significantly correlated with anterior talofibular ligament length but not with peroneal muscle thickness. In the CAI group, all directions of Y-Balance did not correlate with the anterior talofibular ligament length, but the lateral posterior and medial posterior Y-Balance were significantly correlated with the peroneal muscle thickness.

In the CON group, the change of the anterior talofibular ligament length was related to the inhibition of standing balance, whereas the function of the peroneal muscles was the inhibitor of standing balance in the CAI group.

To improve static balance in individuals with CAI, peroneal muscle function needs to be rehabilitated instead of anterior talofibular ligament laxity.