Teaching Case

Fixed pronated forearm.

The patient presented with a history of trauma over his left elbow joint. After the fall he complained of pain and swelling of the lateral aspect of his elbow. Examination revealed a fixed pronated forearm, and inability to supinate the forearm and the hand. Radiographs of the elbow showed an osseus fusion between the proximal ends of the radius and ulna, without evidence of fracture.

Congenital radioulnar synostosis is a relatively uncommon deformity that involves the proximal end of the radius and ulna, and in which the proximal radioulnar joint space fails to form (1). The failure of longitudinal segmentation during the seventh week of development results in a persistent bridge of tissue that connects the proximal end of the radius to the neck of the ulna. Usually this tissue ossifies into an osseus synostosis, although fibrous synostosis can also occur. The synostosis is bilateral in over 60 percent of cases (2), affecting men and women equally or showing slight men predominance (3). The sporadical examples occur more often than familial cases (dominant inheritance) (3). Although most of cases have been isolated, additional anomalies may appear, such as congenital dislocation of the hip, club feet, anomalies of the knee joint, coalescence of the carpal bones, missing or diminutive thumb, symphalangism and Madelung´s deformity (4). The frequent association with other congenital syndromes such as Aperts, Williams, Klinefelter, Nievergelt-Pearlman, and acrocephalopolysyndactyly, supports the idea of the genetic origin (4). Depending of the extent of involvement, two types have been described:
- type I, proximal or true radioulnar synostosis, in which the radius and the ulna are smoothly fused at their proximal borders for a variable distance, usually 2-6 cm, and
- type II, secondary or radioulnar synostosis associated with congenital dislocation of the radial head, in which the fusion is just distal to the proximal radial epiphysis (1). In both types, interference with the ability to supinate the forearm is seen.