The reaction of cartilage and osteophyte formation after the intraarticular injection of papain.

A histological and autoradiographical study on the reaction of chondrocytes and the growing processes of osteophyte after the intraarticular injection of papain was carried out. The degenerating processes--fibrillation, death of chondrocytes and erosion--were observed as early as 1 day after the injection, and acid mucopolysaccharide staining with safranin-O was completely lost throughout the articular cartilage 1 week after the injection. The regenerating or proliferating figures--chondrocytes mitosis, thickening of fibrous tissue--were observed as early as 3 days after the injection and chondrocyte clusters were noted after 1 week of injection. Four weeks after injection, proliferating processes were more obvious than degenerating processes, safranin-O stainability had recovered and the proliferative figures of cartilage and fibrous tissue became more obvious. As blood vessels invaded into the cartilage and thickened fibrous tissue, osteophyte began to form in these tissues. Four types of growing processes of osteophyte were observed. Hypertrophy of articular cartilage was observed, and new hyaline articular cartilage appeared to be formed through metaplasia from fibrous tissue. Including the osteophyte formation, tremendous regenerating or repairing efforts of chondrocytes and fibroblasts were observed. These results appear to indicate that cartilage has some ability to regenerate and to repair itself if it could avoid further damage.