PERONEUS QUARTUS MUSCLE - MR-IMAGING FEATURES

PURPOSE: To determine the prevalence of the peroneus quartus (PQ) musc le, to demonstrate the morphology of this accessory muscle on magnetic resonance (MR) images, and to reassess the reported association of th e PQ muscle with a hypertrophic peroneal tubercle. MATERIALS AND METHO DS: A retrospective review was performed of 136 consecutive ankle MR i maging 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 wa s variable and included the calcaneus, peroneus longus tendon, peroneu s brevis tendon, and cuboid bone. The calcaneus was the insertion site in 11 cases. The accessory tendon attached to the retrotrochlear emin ence of the calcaneus. In the group with the PQ muscle, the retrotroch lear eminence was significantly taller (P < .01) than in the group wit hout the PQ muscle. CONCLUSION: Contrary to previous reports, the pero neocalcaneal variant of the PQ muscle appears to insert in the retrotr ochlear eminence of the calcaneus rather than the peroneal turbercle. The presence of the PQ muscle is associated with a prominent retrotroc hlear eminence but not with an enlarged peroneal tubercle.