Peroneus brevis tendon in normal subjects: MR morphology and its relationship to longitudinal tears.

Purpose: The most prevalent, yet unproven, theory for the development of longitudinal splits of the peroneus brevis tendon is the compression of the peroneus brevis tendon by the peroneus longus tendon in dorsiflexion. The goal of our study was to provide insight into this pathomechanism by evaluating the shape of the peroneus brevis tendon and its relationship to the adjacent structures in the fibular groove during plantarflexion and dorsiflexion.
Method: The MR images of 13 ankles in asymptomatic adult volunteers were performed in full dorsiflexion and plantarflexion. The axial MR images were assessed for the shape of the peroneus brevis tendon and its relationship to the peroneus longus tendon and posterior cortex of the fibula in both plantarflexion and dorsiflexion.
Results: In 12 of the 13 volunteers, the peroneus brevis tendon was located anterior or anteromedial to the peroneus longus tendon in the fibular groove. In those volunteers the peroneus brevis tendon was more flattened and compressed against the fibular groove by the overlying peroneus longus tendon in dorsiflexion than plantarflexion. Fat planes were noted in plantarflexion between the peroneal tendons as well as between the peroneus brevis tendon and the fibular groove. These were obliterated in dorsiflexion.
Conclusion: The changes in configuration of the tendon of the peroneus brevis tendon in dorsiflexion compared with plantarflexion provide support to our present understanding of the pathomechanism of longitudinal tears of the peroneus brevis tendon.