Experimentally induced arthritis using intra‐articular papain

Daily injection of a crude papain solution into the knee joint of young rabbits continued over a six day period resulted in a degeneration of the articular cartilage within two weeks. The initial findings were elevation and loosening of the cartilage in the weight bearing area followed by thinning and fibrillation of the remaining surface. Microscopic changes consisted of disruption of the cartilage adjacent to the subchondral bone and loss of the superficial layers. Changes in the articular cartilage were similar to changes seen in clinical forms of degenerative arthritis.