Painful Os Peroneum Syndrome Presenting as Lateral Plantar Foot Pain

Lateral plantar foot pain can be caused by various entities, and the painful os peroneum syndrome should be considered in the differential diagnosis. Recent developments in musculoskeletal ultrasonography are very useful for initial diagnosis. We discuss a 69-year-old female who experienced lateral plantar foot pain for over one month. Through physical examination, radiography, ultrasound and magnetic resonance imaging, she was diagnosed with the painful os peroneum syndrome with a chronic fatigue fracture of multipartite os peroneum and peroneus longus tenosynovitis, for which she underwent surgery. We herein report this rare condition and reviewed the relevant literature.