Functional Assessment of Peroneal Muscles Using Ultrasound Imaging in Chronic Ankle Instability

Abstract

Background: Lateral ankle sprains (LAS) result in chronic ankle instability (CAI), causing ongoing instability. Although peroneal muscle weakness is documented in CAI, surface electromyography shows similar activation patterns between CAI and healthy individuals, suggesting structural rather than neural deficits. Ultrasound imaging (USI) uniquely enables noninvasive assessment of muscle morphology and quality through cross-sectional area and echogenicity measurements. However, previous USI studies examined peroneals only in nonweight-bearing positions, potentially missing functional deficits. This study examines peroneal muscle characteristics in CAI versus healthy individuals specifically during weight-bearing functional positions using USI. Methods: A case–control study was conducted with 58 participants (29 CAI and 29 healthy controls), aged 18–30 years. Cross-sectional area (CSA), echogenicity (grayscale analysis where higher values indicate fatty infiltration/fibrosis), and functional activation ratio (FAR) of the peroneal muscles were assessed using USI in nonweight-bearing (side lying) and weight-bearing (bilateral-leg standing (BLS) and single-leg standing (SLS)) positions. CSA images were averaged from three measurements for each position. Results: The CAI group had significantly smaller CSA in BLS (p < 0.01) and SLS (p < 0.01) but not lying (p = 0.06), higher echogenicity indicating poorer muscle quality (69.7 ± 10.3 vs. 61.3 ± 7.0, p < 0.01), and lower FAR in both BLS (0.99 ± 0.13 vs. 1.13 ± 0.16, p < 0.01) and SLS (1.01 ± 0.17 vs. 1.12 ± 0.22, p = 0.03) compared to healthy controls. Conclusion: Individuals with CAI showed reduced peroneal muscle CSA, lower activation, and poorer muscle quality specifically in weight-bearing positions compared to healthy controls. These findings suggest altered muscle function in CAI especially in functional weight-bearing positions. This demonstrates the need to assess peroneals in functional weight-bearing position compared to resting.