Aetiopathogenesis of canine elbow osteochondrosis: a study of loose fragments removed at arthrotomy.

Twenty-five ununited coronoid processes (UCP) and 24 osteochondritis dissecans (OD) flaps were examined by light and transmission electron microscopy. Chondrocytes showed degenerative changes but remained viable and continued to secrete matrix components, even though the organisation of the matrix was altered. Differences in the histological and ultrastructural appearance of the two lesions tend to suggest that they are two separate disease entities, although they may occur together in the same joint. It is hypothesised that OD results from incorrect cartilage maturation and endochondral ossification. The aetiology of UCP is unclear but there is a possibility of its being a subchondral fracture, with an ineffective fibrous repair in some cases.