Congenital radioulnar synostosis is a rare but challenging congenital elbow anomaly. Patients have severe restriction of forearm rotation, but most patients do not report flexion-extension limitation. Here we report the case of an 11-year-old boy with congenital radioulnar synostosis. He had painful snapping of the right elbow. Painful snapping, and locking occasionally, occurred at the right elbow during flexion of the elbow from extension. There was no history of trauma. Magnetic resonance imaging showed tissue structure between the radial head and capitellum. Open surgery was performed. We found a hypertrophic annular ligament between the radial head and capitellum. During flexion, the ligament got trapped between the radial head and capitellum. The hypertrophic ligament was removed. After the surgery, the patient had no recurrence of snapping or locking.
Keywords: Congenital, radioulnar synostosis, annular ligament