A Proximal Fibularis Brevis Muscle Is Associated with Longitudinal Split Tendons: A Cadaveric Study

The anomalous distal musculotendinous junction of the fibularis brevis muscle has been hypothesized to contribute to the development of longitudinal fibularis brevis tendon tears. Specifically, the mass effect of the low-lying fibularis brevis muscle belly was thought to increase the pressure on the superior peroneal retinaculum and increase the probability of fibularis brevis tendon subluxation. A more recent examination of the fibularis brevis tendon junction found, contrary to this hypothesis, a statistically significant association between an anomalous proximal musculotendinous junction and the prevalence of longitudinal split tears. However, no rationale was offered. The present study examined the relationship between the musculotendinous junction and the prevalence of longitudinal fibularis brevis tendon tears. A total of 24 fibularis brevis tendon lengths were measured bilaterally in 12 human cadaveric specimens. The tendon lengths were assessed as the vertical distance from the most inferior aspect of the lateral malleolus to the most distal fibularis brevis musculotendinous extension. Only full-thickness tears were identified and included. The lengths of tendons with and without longitudinal tears were compared. Of the 24 tendons examined, 7 (29%) presented with full-thickness longitudinal tears from 4 cadavers (33%). The mean length for the tendons with tears was significantly longer (p < .001) than the mean length of those without tears (28.86 ± 3.02 mm versus 16.29 ± 7.30 mm). Our research concurs with the most recent findings, identifying a statistically significant association between an anomalous proximal muscle belly extension and longitudinal fibularis brevis tendon tears. Furthermore, we propose the hypothesis that a more proximal musculotendinous junction might predispose individuals to a lesser stabilizing effect of the muscle against the posterior lateral surface of the fibula, increasing the probability of anterolateral subluxation, attrition, and longitudinal tear development.