Cartilage and bone morphology in osteochondritis dissecans.

Osteochondritis dissecans (OD) is a syndrome that can be characterized as a non-infectious disturbance of enchondral ossification or as a post-traumatic event. OD occurs in the joint cartilage and physis of long bones, as well as in the talus or metacarpal head especially of young athletes. The medial femoral condyle is the most commonly affected site. The causes of osteochondritis dissecans are poorly understood. Thirty human osteochondral cylinders from patients (aged 16-44 years) with osteochondritis dissecans of the medial femoral condyle (grades IV and V according to Rodegerdts and Gleissner) were harvested intraoperatively from osteochondritic areas as part of a cartilage-bone transplantation. Light microscopy, electron microscopy, and immunohistochemistry using poly- and monoclonal antibodies against collagens and glycosaminoglycans revealed differences between osteochondrotic and normal cartilage. Staining with toluidine blue at pH 1 shows a decrease in acidic glycosaminoglycans in OD. Modified pentachrome staining showed a thinned subchondral growth plate compared to normal osteochondral samples. Borders to the healthy tissue are clearly visible micro- and macroscopically. Scanning electron microscopy revealed structural differences in the subchondral area. Immunohistochemistry found a general decrease in glycosaminoglycan content and a change in composition. Only faint staining for chondroitin and keratan sulfates was observed in osteochondritic cartilage, whereas increased staining was shown for keratan sulfate in bone.