Pathogenesis of epiphyseal osteochondrosis.

Osteochondrosis (OC) of the articular epiphyseal cartilage complex (AECC) is a developmental disease that is present in the first weeks of life. It is characterized by focal chondronecrosis and retention of growth cartilage due to failure of endochondral ossification. Fissures may extend from the lesion through the overlying articular cartilage to create a cartilage flap and an osteochondral fragment. This articular form is known as osteochondritis dissecans (OCD). There have been many hypotheses about the etiopathogenesis of OC of the AECC including, amongst others, ischemia of growth cartilage or altered cartilage type II collagen metabolism. The ischemia theory proposes that necrosis of the vessels in the cartilage canals of the sub-articular growth cartilage leads to necrosis of chondrocytes and retention of necrotic cartilage. Several studies have measured biomarkers in serum and synovial fluid to demonstrate a consistent increase in type II collagen synthesis in young animals of different species. Although these changes could represent lesion reparative events, there is no comparable increase in the synthesis of cartilage matrix proteoglycan molecule. It is therefore speculated that an altered type II collagen metabolism may be involved in the early changes associated with OC. Further studies of OC susceptible animals in utero and the first weeks of life are required to elucidate the cause of vessel necrosis and the exact role of type II collagen structure and metabolism in OC.