Early lesions of articular osteochondrosis in the distal femur of foals.

Failure of the cartilage canal blood supply to epiphyseal growth cartilage has been implicated in the pathogenesis of articular osteochondrosis in horses and other animal species. In a previous study of the developmental pattern of the blood supply in the tarsus of foals, early lesions of osteochondrosis were consistently found in regions where the cartilage canal vessels traversed the chondro-osseous junction. The developmental pattern of blood vessels has also been described in the distal femoral epiphysis; however, the group of foals examined in that study did not have lesions of osteochondrosis in this location. Therefore, the relationship between the occurrence of early lesions of osteochondrosis and the developmental pattern of the blood supply to epiphyseal growth cartilage in this site in foals has not been examined. Distal femora were collected from 30 fetuses and foals (up to 11 months old) submitted for postmortem examination. Sections from the lateral trochlear ridge and medial femoral condyle of both hind limbs were examined histologically. Sixteen cartilage lesions were found in 7 of the 30 fetuses and foals. All lesions contained evidence of cartilage canal necrosis and ischemic chondronecrosis. The lesions were located in regions where cartilage canal vessels traversed the chondro-osseous junction, as previously observed in the tarsus. The location and morphology of lesions indicated that a subclinical stage of ischemic chondronecrosis existed that preceded and predisposed to the development of osteochondrosis dissecans and subchondral bone cysts.