Alterations in the distal extension of the musculus peroneus brevis with foot movement.
OBJECTIVE: A low-lying belly of the musculus peroneus brevis (presence of muscle tissue within the fibular groove) is said to be a risk factor for rupture or dislocation of the peroneal tendons. However, alterations in foot position may affect the position of the musculotendinous junction. The purpose of this study was to evaluate the normal position of the musculotendinous junction of the musculus peroneus brevis in full dorsiflexion and plantar flexion. MATERIALS AND METHODS: The ankles of 12 adult asymptomatic volunteers were imaged in full dorsiflexion and plantar flexion. The number of scans between the fibular groove and the first scan imaging the muscle belly of the musculus peroneus brevis was documented in each patient in full dorsiflexion and plantar flexion. RESULTS: Distal extension of muscle belly into or beyond the fibular groove was present in 11 subjects in dorsiflexion and in seven subjects in plantar flexion. CONCLUSION: Extension of the muscle belly of musculus peroneus brevis into and distal to the fibular groove is part of the normal excursion of the muscle during foot motion. Care should be taken not to misdiagnose this normal finding as a pathologic condition when interpreting MR studies of the ankle.