Peroneus quartus muscle: MR imaging features

PURPOSE: To determine the prevalence of the peroneus quartus (PQ) muscle, to demonstrate the morphology of this accessory muscle on magnetic resonance (MR) images, and to reassess the reported association of the PQ muscle with a hypertrophic peroneal tubercle. MATERIALS AND METHODS: A retrospective review was performed of 136 consecutive ankle MR imaging studies. The origins, insertions, and variations in size of the muscle and the dimensions of the peroneal tubercle and retrotrochlear eminence were recorded. RESULTS: The prevalence of the PQ muscle was 10% (14 of 136 cases). The accessory muscle and tendon unit descended medial and posterior to the peroneal tendons. The site of insertion was variable and included the calcaneus, peroneus longus tendon, peroneus brevis tendon, and cuboid bone. The calcaneus was the insertion site in 11 cases. The accessory tendon attached to the retrotrochlear eminence of the calcaneus. In the group with the PQ muscle, the retrotrochlear eminence was significantly taller (P < .01) than in the group without the PQ muscle. CONCLUSION: Contrary to previous reports, the peroneocalcaneal variant of the PQ muscle appears to insert in the retrotrochlear eminence of the calcaneus rather than the peroneal turbercle. The presence of the PQ muscle is associated with a prominent retrotrochlear eminence but not with an enlarged peroneal tubercle.