Radiology of postnatal skeletal development. IV. Distal radius and ulna.

Thirty-one pairs of distal radioulnar units were obtained from human cadavers ranging in age from full-term neonates to fourteen years. These were studied morphologically and radiographically. Specimen roentgenography using air/cartilage interfacing demonstrated the osseous and cartilaginous portions of the epiphyses. These roentgenographic aspects of development are discussed and illustrated to provide a reference index. The radial and ulnar physeal/metaphyseal contours initially are transverse. Progressively the distal radius develops a proximally directed curve adjacent to the radioulnar joint. Both physes subsequently develop a convex contour with mild undulations, and a central concavity associated with the secondary ossification center. Longitudinal ossification striations were observed crossing the distal ulnar physis. These appear to be normal. At no time during postnatal development did the distal ulna ever articulate directly with the carpus. It was always separated by a segment of triangular fibrocartilage connecting the ulnar styloid to the distal radial epiphysis. This was never perforated. This discoid cartilaginous structure is the anatomic cause of the concomitancy of ulnar styloid fractures with distal radial epiphyseal injuries, an injury pattern which may occur prior to ossification in the ulnar styloid, and which may lead to non-union of the styloid when ossification eventually occurs. In none of the specimens was an accessory ossification center present in either the radial or ulnar styloid process.