Observations on the postnatal morphogenesis of the porcine humeral condyle and the pathogenesis of osteochondrosis.

The condyles of the distal humeri of 75 pigs ranging in age from 1 day to 9 months were studied by gross observation and radiography. Twenty-eight pigs were reared on pasture, necropsied, and were studied histologically. The portion of the secondary center of ossification of the distal humeral epiphysis located in the lateral condyle of neonatal pigs was larger than that observed in the medial condyle and assumed the contour of the articular surface at an earlier age. Thus, the articular-epiphyseal cartilage of the medial condyle had an inherent propensity to be thicker than that of the lateral condyle and might be predisposed to the influence of deleterious biomechanical insult. Projections of cartilage containing degenerating chondrocytes from the epiphyseal cartilage into the subadjacent trabecular bone may have been early lesions of osteochondrosis in pigs less than or equal to 3 months of age. Osteochondral and articular fractures of the medial condyles and intercondylar cristae of the distal humeri of 6- to 9-month-old pigs were observed. Seemingly, fractures resulted from shearing forces within the humeral articular surfaces at the junction of the articular-epiphyseal cartilage continuum and the subchondral epiphyseal bone with subsequent separation of the tissues at the osteochondral interface. Such shearing forces could result from a torque and/or laterally to medially directed forces of unusually great magnitude generated by movement of the proximal radius against the distal humerus.(ABSTRACT TRUNCATED AT 250 WORDS)