Acute dislocation or subluxation of the peroneal tendons is an uncommon injury that has a traumatic cause. Sport participation is responsible for about 92% of acute peroneal dislocations. Skiing has been reported to cause approximately 66% of the sports injuries.10 Peroneal tendon dislocation may be difficult to distinguish from an acute ankle sprain, but it is rare for both to occur simultaneously. The acute dislocation is caused by a sudden forceful dorsiflexion with simultaneous "violent" reflex contraction of the peroneal muscles. With skiing injuries, the mechanism has been described as forceful peroneal contraction occurring with sudden deceleration and ankle dorsiflexion as the ski tips dig into the snow. Acute injuries frequently exhibit ecchymosis, tenderness, and swelling over the lateral aspect of the ankle and may look similar to a high ankle sprain. Most patients are unable to describe the mechanism of injury, as opposed to lateral ankle sprains, where most are able to describe an inversion injury. There are several findings on physical examination that help make a distinction between lateral ankle sprain and peroneal dislocation; typically, the tenderness is posterior to the fibula with acute dislocation versus anterior over the anterior talofibular ligament or anterior tibiofibular ligament with a sprain. Patients may complain of a painful "snapping" sensation and have apprehension on resisted dorsiflexion and eversion with dislocation. The anterior drawer sign should be negative in peroneal dislocation.
Eckert and Davis11 described a classification of acute peroneal tendon dislocation after exploring 73 cases. In grade I injuries, the superior retinaculum and periosteum are stripped off the posterior lateral border of the fibula. The peroneus longus dislocates anteriorly, sitting between the periosteum and the fibula. In grade II injuries, the fibrous rim of the superior peroneal reti-naculum is avulsed along with the periosteum of the fibula, mim icking a Bankart lesion in the shoulder. The peroneus longus dislocates anteriorly. In grade III injuries, a bony rim fracture involving the posterior lateral corner of the fibula along with the periosteum and fibrous rim are avulsed by the retinaculum. None of these 73 cases had an actual tear of the superior peroneal retinaculum.
In chronic peroneal tendon dislocation, the ankle may appear normal. This injury should be suspected when there is a history of pain with unusual "popping." A popping or snapping sensation is often reproducible with dorsiflexion and eversion of the foot. Slight swelling and tenderness are usually present posteriorly, and if more significant pain is noted, a tendon tear should be suspected. There may be a complaint of instability, yet the anterior drawer and talar tilt tests remain normal.
Standard weight-bearing anteroposterior, lateral, and mortise radiographs should be obtained and inspected for a flake or fibular cortex rim fracture. This finding on radiographs is pathognomonic of grade III tendon dislocation and is found in 10% to 30% of cases.
Tenography, computed tomography, and MRI have been used to diagnose peroneal tendon dislocations, with MRI currently the study of choice. MRI has the best ability to define soft-tissue structures including the peroneal tendons, superior retinaculum, and inferior retinaculum.
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