Pretest

Introduction

Congenital synostosis of the proximal radius and ulna represents a failure of longitudinal segmentation during intrauterine development. Present at birth, the deformity becomes obvious in early adolescence as the synchondrosis between the radius and ulna begins to ossify. While the etiology is unknown, a genetic basis for the disorder is suspected; positive family histories have been reported. An association with other musculoskeletal anomalies such as club feet and developmental dysplasia of the hip is not uncommon. Congenital radioulnar synostosis is often seen in syndromes including acropolysyndactalyism (Carpenter's Syndrome), acrocephalosyndactylism (Apert's Syndrome), arthrogryposis and chromosomal abnormalities, especially Klinefelter's Syndrome.

Presentation

The typical patient presents in childhood with functional complaints including difficulty manipulating buttons or belt buckles while dressing, hand and wrist positioning while holding objects, and poor upper extremity dexterity in sports. Approximately 60% of patients have bilateral deformities. On physical examination, the elbow often has a small flexion deformity in association with shortening of the forearm in unilateral cases. The forearm is fixed in variable degrees of pronation, in the majority of cases. Rotational hypermobility of the wrist is commonly seen as a compensatory mechanism for loss of supination.

Radiologic Features

Radiographic appearance of congenital radioulnar synostosis varies from a short proximal radioulnar fusion with minor radial head deformity to nearly complete longitudinal fusion of the radius and ulna (Slide 9). Most commonly, the radius and ulna are fused for a short distance proximally. Dislocation of the radial head is occasionally seen when the synostosis occurs distal to the radial head epiphysis. Long synostosis are accompanied anatomically by absence of the pronator teres, pronator quadratus, supinator and brachio-radialis muscles.

Treatment

Division of the radioulnar synostosis, done in hopes of restoring forearm rotation, is generally not successful; multiple techniques have been described. While some motion is initially gained, resynostosis commonly occurs. Derotational osteotomy of the radius and ulna is the only useful procedure for congenital radioulnar synostosis. The goal of surgical treatment is to place the forearm, hand and wrist in a more functional, fixed position.
 

Derotational osteotomy is indicated for fixed pronation of 60°, for either bilateral or unilateral deformities, in a child with significant functional limitations. Proximal radial and ulnar osteotomies are performed. The forearm is then fixed in approximately 20° of pronation in unilateral cases. In bilateral cases, the dominant hand is placed in approximately 30° of pronation and the nondominant hand in neutral position. Vascular compromise may limit the amount of derotation that can be achieved. Two-stage correction, ulnar shortening and gradual rotational correction by external fixation devices have been described to overcome potential vascular complications.

Bibliography

Busch MT. Sports medicine in children and adolescents. In: Morrissy RT, Weinstein SL, eds. Lovell and Winter's Pediatric Orthopaedics. 5th ed. Philadelphia, Pa: Lippincott Williams and Wilkins; 1996:1273.