The dynamics of peroneus brevis tendon splits: a proposed mechanism, technique of diagnosis, and classification of injury.

The etiology of peroneus brevis splits is unclear. Because longitudinal splits in the peroneus brevis tendon do not necessarily effect the integrity or strength of the tendon, it is difficult to ascertain whether or not injury to the peroneus brevis tendon is present. Recent clinical, anatomic, and histologic reports have suggested that the split develops from prolonged mechanical attrition within the fibular groove as a result of ankle trauma with resultant lateral ankle instability and incompetency of the superior peroneal retinaculum with resultant subluxation of the peroneal tendons. This cascade of events may result in splitting of the peroneus brevis tendon. The purpose of this paper was to report the investigation of the mechanism by which peroneus brevis splits develop, to describe a technique of diagnosis, and to propose a classification of injury. Peroneus brevis splits are the result of a dynamic mechanical insult at the fibular groove. Laxity of the superior peroneal retinaculum combined with peroneus longus mechanical compression causes the peroneus brevis to splay out and eventually split over the sharp posterior edge of the fibula. Anatomic factors, such as a shallow fibular groove (congenital convex groove) or the presence of an anomalous low-lying peroneus brevis muscle belly or peroneus quartus tendon, may also play a role in this mechanism by interfering with the competence of the superior peroneal retinaculum.