Long-term effects of chondrocyte death on rabbit articular cartilage in vivo.

The effects of freezing localized areas of rabbit articular cartilage in vivo were studied at two to twelve months morphologically (gross and microscopic examination, including scanning electron microscopy), histochemically (toluidine blue and safranin O), and metabolically (35S uptake). Up to six months the frozen cartilage was intact but appeared to be dead, as shown by the absence of stainable chondrocytes, severely decreased acid mucopolysaccharide content, and absence of significant uptake of 35S. At twelve months fibrillation and softening were evident, clusters of new chondrocytes with surrounding acid mucopolysaccharides were visible microscopically, and scanning electron microscopy revealed an irregular pattern of collagen fibers which were larger than normal, of varying thickness, and broken in some areas. These changes resembled those seen in degenerative joint disease.