Radiology of postnatal skeletal development

Thirty-six pairs of proximal radioulnar and elbow units from cadavers and prepared skeletons ranging in age from full-term neonates to fourteen years, were studied morphologically and roentgenographically. Air/cartilage interfacing was used to demonstrate the osseous and cartilaginous portions of the developing epiphyses. These roentgenographic aspects are discussed and illustrated to provide a reference index.The articular interrelationships and basic contours of the distal humerus, proximal ulna, and proximal radius are the same throughout postnatal development. The major changes are proportional volume increase and the progressive development of the secondary ossification centers. Because of overlap of the developing secondary ossification centers, roentgenographic interpretation may be difficult. Awareness of the developmental stages and variations should assist in the diagnosis of trauma to the immature elbow.During the first few years the proximal ulnar metaphysis is usually at the midpoint of the ulnohumeral joint in a lateral roentgenogram with the elbow flexed at 90°. With further growth and maturation this region of the metaphysis extends proximally. However, such extension is quite variable. The secondary ossification center, which will form most of the olecranon at skeletal maturity, initially forms adjacent to the dorsal side of the metaphysis. Multifocal ossification, while a relatively common clinical observation, was not seen in any of the specimens.The radial head is intra-articular, as is part of the neck (metaphysis). However, attachments of the capsule are such that none of the ulnar metaphysis is intra-articular. The proximal radius has the same contours and relative proportions of head and neck throughout postnatal development. The head is always larger than the neck. However, the contours of the sides of the radial head are of variable obliquity, allowing different degrees of excursion of the annular ligament during rotation (supination-pronation), a factor that anatomically predisposes young children to nursemaid's elbow.The secondary ossification center of the proximal radius initially appears as a linear focus centrally located adjacent to the metaphysis. This progressively expands, but not always symmetrically. The concavity of the articular cartilage may be reflected in a central identation of the ossification center, but this is not usually evident until ten to eleven years. The plane of the articular surface is not at a right angle relative to the longitudinal axis of the radius; instead, there is an increased angulation toward the bicipital tuberosity. This also is a factor predisposing to nursemaid's elbow in the young child.