Morphology of normal and osteochondrotic porcine articular-epiphyseal cartilage. A study in the domestic pig and minipig of wild hog ancestry.

Osteochondrosis is a generalized skeletal disorder that affects the growth cartilage in the growing domestic pig but not in the minipig of wild hog ancestry. In the present study, we compare the ultrastructure of the articular and epiphyseal growth cartilage in the domestic pig with that in the minipig. The domestic pigs had areas of enlarged epiphyseal cartilage with chondronecrosis, which had caused focal impairment of the endochondral ossification, with retention of cartilage in the subchondral bone. Areas of chondronecrosis close to blood vessels were found in the resting zone, with no evidence of thickened cartilage or impaired ossification. The chondronecrosis was surrounded by chondrocytes, organized in small clusters, containing many lipid droplets. The vascular channels adjacent to the chondronecrosis contained degenerated blood vessels. The minipigs showed no areas of enlarged epiphyseal cartilage. A few dead chondrocytes could be seen close to vascular channels which contained morphologically normal blood vessels. We conclude that restricted perivascular chondrolysis may occur in the pig without the presence of vascular degeneration and without progressing to osteochondrosis.