Cyst-Like Lesions at Chondro-Osseous Junction.

This study described and histologically characterized a cyst-like lesion (CLL) at the chondro-osseous junction. Rat knees (n = 12), with or without excessive running-induced osteoarthritis (OA), were used for counting the incidence, morphological measurements, immunohistochemistry of the CLL. A typical CLL, appearing as a void space in the matrix, was located on the tidemark at the chondro-osseous junction. The content of the CLL included types II and VI collagen, proteoglycans but not intact chondrocytes. At least one CLL was found in 5/6 osteoarthritic knees and only 2/6 in the non-osteoarthritic knees. The margin of the CLL was depleted of proteoglycans. The chondrocytes around the lesion were deformed and occasionally apoptotic. Matrix metalloproteinase 13 and vascular endothelial growth factor receptor were not detected in and around the CLL. CLLs disrupt the integrity of cartilage at a mechanically critical location-the chondro-osseous junction. The significance of the CLL in cartilage biology and its potential role in OA pathogenesis warrant further investigation.