Increased Peroneus Longus Muscle Thickness During Maximal Voluntary Isometric Contraction in Individuals with Chronic Ankle Instability Compared to Healthy Controls

This study aims to investigate the differences in muscle thickness and pennation angles of the peroneus longus (PL) and brevis (PB) between individuals with CAI and healthy controls at varying activation levels (0%, 50%, and 100%).

Eleven individuals with CAI (age: 25.3 ± 6.0 years) and nine healthy controls (age: 24.7 ± 5.7 years) participated in this study. A high-resolution musculoskeletal ultrasound with a linear probe was used to assess the morphology of the PL and PB muscles at the proximal one-third of the distance between the fibular head and the lateral malleolus. Ultrasound measurements were taken in a side-lying position and the ankle in a resting position (0% of maximal voluntary isometric contraction (MVIC)). A force gauge was secured around the forefoot, and one MVIC of ankle eversion was performed before data collection. A real-time visual feedback of force was displayed on the screen to help participants maintain 50% and 100% of their MVIC for 3 seconds, and the muscle morphology was measured simultaneously. The pennation angle and the thickness of PL and PB were processed by offline software (Fiji, v1.54f). The independent t-test was performed to assess the differences between CAI and healthy control, with a significance level of p 0.05.

The finding showed a significant difference between CAI and healthy control in the thickness of PL at 100% of MVIC (CAI: 0.83 ± 0.14 cm; Healthy control: 0.68 ± 0.17 cm, p = 0.043). There was no significant difference in 0% of MVIC in pennation angle (PL: p = 0.553; PB: p = 0.389) and thickness (PL: p = 0.197; PB: p = 0.197), 50% of MVIC in pennation angle (PL: p = 0.791; PB: p = 0.260) and thickness (PL: p = 0.111; PB: p = 0.259), and 100% of MVIC in pennation angle (PL: p = 0.390; PB: p = 0.990) and thickness of PB (p = 0.186) between groups.

This study demonstrated that individuals with CAI exhibit a significantly greater PL muscle thickness at 100% MVIC compared to healthy controls. However, no significant differences were observed between the CAI and control groups in the pennation angle or muscle thickness of both the PL and PB at lower activation levels (0% and 50% MVIC).

This finding highlights the potential role of targeted neuromuscular training programs for CAI patients, emphasizing the need to improve control of higher levels of PL activation to enhance joint stability.