Acute peroneal tendon dislocation occurs at the retrofibular groove during tendon loading. This commonly occurs from sudden, reflexive contraction of the peroneal muscles during dorsiflexion of the foot, with or without inversion, or from forced dorsiflexion of the everted foot. The result is the rupture of the superior peroneal retinaculum (SPR) and anterior dislocation of the peroneal tendons anteriorly.
Peroneal tendon subluxation is typically the result of a similar mechanism of injury that results in partial injury to the SPR. Instability of the peroneal tendon results in displacement within the retrofibular groove without overt dislocation of the tendons.
Classic history and presentation: The etiology of peroneal tendon subluxations or dislocations is usually trauma during a sporting event involving cutting. Patients may report a snapping or popping sensation around the lateral malleolus, and patients are rarely able to continue activities or to ambulate afterward. Typical presentation includes tenderness and swelling around the lateral malleolus (predominantly at the retrofibular groove), feelings of instability on uneven surfaces, and weakness of active eversion. Recurrent or chronic subluxation of the peroneal tendons may present with instability and clicking of the lateral surface of the ankle as the tendons sublux anteriorly.
- Age – These injuries most commonly occur among young athletes, although patients' ages from these studies range up to 57 years.
- Sex / gender – Previous retrospective cohort studies and case series have reported cases of peroneal tendon subluxations or dislocations predominantly in men.
Pathophysiology: Violent contraction of the peroneal muscles occurs to overcome the restraining superior peroneal retinaculum. There have been reports that the peroneal muscle contraction ruptures the superior peroneal retinaculum, while other studies have shown that the retinaculum remains intact and is stripped off the lateral malleolus. If the injury remains undiagnosed, untreated subluxation or dislocation can lead to recurrent dislocation, tendinitis, fraying, tearing, and rupture of the peroneal tendons.
Grade / classification system: Eckert and Davis first classified superior peroneal retinaculum tears, which was later expanded by Oden, who added a fourth grade.
Classification of superior peroneal retinaculum tears –
- Grade I: Elevation of the superior peroneal retinaculum from the lateral malleolus. The tendons slip into the space between the periosteum and bone.
- Grade II: Elevation of the fibrocartilaginous rim (Bankart-type injury). The tendons slip between the fibrocartilaginous rim and the fibula.
- Grade III: A cortical rim fragment becomes avulsed from the fibula, with the tendons becoming dislocated between the fragment.
- Grade IV: The superficial peroneal retinaculum is torn from its posterior calcaneal attachment and deep investing fascia of the Achilles tendon. The retinaculum lies deep to the dislocated tendon.