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Developmental anterior dislocation of the radial head resulting from a congenital solitary osteochondroma of the proximal ulna in an infant.

A 4-month-old female infant was brought to our office by her parents, who had noticed a lump on the child's right elbow. Examination revealed a hard, painless lump in the antero-external region that was not reducible in flexion-extension or in pronation-supination. Neither palpation nor passive motion produced pain. Preoperative radiographs revealed a bony mass in the anteroexternal region of the proximal ulnar metaphysic (solitary osteochondroma), which was displacing the radial head into anteroexternal dislocation. No physiological bowing of the proximal metaphysis of the ulna was present. The infant underwent surgery at 6 months of age. No remains of the annular ligament were found. A complete resection of the tumour mass was performed, after which it was possible to reduce the radial head, together with the humeral condyle. Trans-radiocapitellar fixation was applied, with immobilization for 6 weeks. Subsequent radiological study revealed a congruent reduction of the radial head, with a progressive periosteal reaction of the posterior cortex of the ulna that evolved towards remodeling of the physiological bowing. Eight years after the surgery, the child remains asymptomatic, with complete range of motion and symmetric carrying angles. There were no relapses of osteochondroma, the deformity, or radioulnar synostosis.