Imaging description

Peroneal tendon dislocation can be diagnosed by a characteristic avulsion fracture off the lateral aspect of the distal fibula (Figure 65.1). A small elliptic bony fragment is avulsed from the attachment site of the superior peroneal retinaculum, which keeps the peroneal tendons in place behind the retrofibular groove. Advanced imaging studies including ultrasound, CT (Figure 65.2), and MRI can demonstrate dislocation of the peroneal tendons. Ultrasound is an effective technique to dynamically detect transient peroneal tendon dislocation. Dynamic scanning of ultrasound is performed with the foot dorsiflexed and everted passively and actively from a plantarflexed and inverted position. Static cross-sectional imaging with CT and MRI is less reliable for detecting transient dislocation.

Importance

Peroneal tendon dislocation can be complicated with fractures of the ankle and foot. Calcaneal fractures are commonly associated with peroneal tendon dislocation. As CT is frequently performed for patients with calcaneal fractures to evaluate surgical indications and pre-operative planning, peroneal tendon dislocation should be sought for those patients as it may influence the treatment and prognosis.

Typical clinical scenario

Calcaneal fractures are typically produced by axial force resulting from deceleration such as a fall from a height or a motor vehicle accident. Males are more often affected than females. The fracture pattern is affected by the magnitude and direction of the impacting force, foot position, and bone mineral content. The reported incidence of peroneal tendon dislocations in patients with calcaneal fractures is between 25% and 47.5%. The incidence of peroneal tendon dislocations increases with the grade of Sander’s classification, which reflects the severity of calcaneal fractures. Peroneal tendon dislocation may reduce or persist after the subtalar joint reduction and fixation of the calcaneus.