Peroneus Quartus Muscle.

The peroneus quartus (PQ) muscle is a rare but sometimes missed potential etiology of ankle pain and tendon subluxation. We report the case of a 16-year-old boy who presented with lateral right ankle pain and subluxation of peroneal tendons. He had a history of non-Hodgkin lymphoma and palpable distal fibular osteochondroma. Seven months after excision of the exostosis and repair of the peroneal tendon retinaculum, the pain recurred. Imaging showed a split peroneus brevis (PB) tendon. During surgery, a PQ muscle was found and excised, and the PB tendon was repaired. One year after surgery, the patient's symptoms were resolved.