Radiology of postnatal skeletal development. V. Distal humerus.
Thirty-one pairs of distal humeri were obtained from human cadavers ranging in age from full-term neonates to fourteen years. These were studied morphologically and roentgenographically. Specimen roentgenography using air/cartilage interfacing demonstrated both osseous and cartilaginous components of the epiphyses. These roentgenographic aspects of development are discussed and illustrated to provide a basis reference index. The supracondylar region is characterized by a fossa which initially is in both metaphysis and epiphysis, but migrates to the metaphysis completely within the first year. On either side of the fossa are osseous columns, which contrast with the broad metaphyseal bone above the columns. Within the fossa, anteriorly and posteriorly, are fat pads which may be elevated by intraarticular hematoma or reactive joint fluid. The physeal contour initially is transverse and smooth. Lappet formation progressively demarcates the epicondylar physeal regions, with the medial one becoming a functionally, but not histologically separate region. The capitellum is the first region to develop a secondary ossification center. This progressively expands into the trochlear portion of the epiphysis, a factor which predisposes to lateral condyle fracture propagation across the trochlear articular surface. The trochlea characteristically ossifies by multiple foci which fuse over time, often creating an irregular appearance to the developing ossification center. Epicondylar ossification tends to be from solitary foci. The lateral epicondylar center fuses with the capitellar center, whereas the medial epicondyle tends to be functionally separate entity throughout development and does not normally fuse to the trochlear ossification center.