Assessment Of Anatomical Variation In Fibularis Brevis and Fibularis Longus Muscle Fiber and Tendon Morphology As a Risk Factor for Ankle Instability and Injury

Abstract

Variations in lateral ankle anatomy may predispose individuals to injury in certain foot positions or activities. The orthopedics literature notes that a “low‐lying muscle belly” of the fibularis brevis muscle, defined by some as extending distal to the tip of the lateral malleolus, is a risk factor for fibularis brevis tendon injuries. Past studies document this finding in pathologic ankles during clinical evaluation and treatment. However, the normal range of variation in fibularis brevis (FB) and fibularis longus (FL) muscle fiber and tendon morphology is unknown.The goal of this study was to survey a cadaveric sample for normal gross anatomical variations in muscle fiber and tendon morphology of the FB and FL muscles and to analyze these traits with respect to body size and sex in a general population.We dissected 66 preserved foot and leg specimens from a mixed‐sex sample of 33 adult individuals to analyze soft tissue variation in the lateral ankle region. No evidence of tearing or splitting was grossly observable in any of the tendons. All specimens appeared to have intact superior and inferior fibular retinacular complexes. We took twelve linear measurements on each specimen with the foot in 90° dorsiflexion. We performed Pearson's correlation analyses of muscle fiber dimensions against foot length as a body size surrogate. We also performed two‐tailed, t‐test contrasts between female and male size‐controlled measurement means to test for sex‐related differences.The muscle fibers on the anterior and posterior surfaces of the FB and FL muscles typically terminate at different locations. In two females and four males, the posterior surface fibers of the FB muscle on the right and/or left sides terminated inferior to the tip of the lateral malleolus. In all other cases, the FB and FL muscle fibers terminated superior to the fibular tip. There were no statistically significant differences between size‐controlled mean female and male muscle fiber dimensions. However, in females, the extents of the right and left FL muscle fibers were significantly moderately to strongly correlated with foot length (r=0.52–0.71; p=0.004–0.05). In females, the extent of the right posterior surface FB fibers were also significantly moderately correlated with foot length (r=−0.59; p=0.02), but negatively. No significant correlations between muscle fiber extent and body size were detected in the male sample.There is weak evidence for a body size effect in FB and FL muscle fibers in females, but no evidence for overall sex‐related or body size effects in the morphology of these muscles. Our findings along with the historical documented presence of FB muscle fibers extending into and distal to the fibular groove in pathological individuals supports the contention that this condition may predispose an individual to ankle injury. However, the lateral ankle is a complex structure and multiple factors are likely to be involved in ankle instability.Support or Funding InformationMidwestern University, Federal Work‐Study ProgramThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.