Locking of the forearm in pronation due to extensor carpi ulnaris tendon dislocation with dorsal distal ulna dislocation.

A 13-year-old girl occasionally felt pain on the ulnar side of her right wrist before her right forearm abruptly locked in the pronated position while playing basketball. She had no pain or swelling after the injury; and after a month of therapy, she was seen at our hospital. On physical examination, the right forearm was locked in 70” pronation. When supination was attempted, the patient felt pain and the forearm remained fixed in pronation. X-ray films showed an ulna plus configuration and a dorsal dislocation of the distal ulna (Fig. 1). Our preoperative diagnosis was that dislocation of the distal ulna caused the locking, and we planned to reduce the distal radioulnar joint dislocation and shorten the ulna. At surgery, the ECU tendon was