Post-traumatic radioulnar synostosis is infrequent, especially following an isolated ulnar shaft fracture, it is very rare. The patient was a 48-year-old man, who was injured by taffic accident. 6 months after intramedullary fixation of the right ulna, he complained of restriction of active or passive forearm rotation. An examination showed that his forearm was fixed in neutral position. 10 months after the osteosynthesis, we treated him surgically with excision of the synostosis, encircling of raw surface of ulna by a silastic sheet and transplantation of free fat. At present, 10 months after the operation, he has gained an active range of motion of 40° pronation and 45° supination. He was graded excellent by Vince and Miller's evaluation, but we should follow him up because of a new bone formation of the synostosis.
