The Peroneus Quartus Muscle in a Locking Phenomenon of the Ankle: A Case Report.

We present the case of a 64-year-old female who was referred to us with an unexplained clicking and locking phenomenon of the right ankle. The magnetic resonance imaging findings suggested a longitudinal tear of the peroneus brevis tendon. During tendoscopy, not only was a Raikin type B intrasheath tendon subluxation visible, but also a peroneus quartus muscle. The peroneus brevis tear was tubularized and the peroneus quartus muscle resected, which resolved the patient's complaints.