Humoral aspects are being discussed in the initiation of arthritis. Therefore, the effects of the proteolytic enzyme elastase on the cartilage of knee joints in rabbits have been investigated. The enzyme was evaluated using activities comparable to those in post-traumatic knee joint hemarthrosis in humans.
Polymorphonuclear leukocyte elastase was injected into one of the knee joints of 10 rabbits. In 5 animals (first study group), joints were then immobilized with a cast for 6 weeks. In the other 5 (second study group), no immobilization was applied. In the first zero group (2 animals), 0.9 % NaCl was injected intra-articularly without immobilization, whereas in the second zero group (2 anmals) knees were immobilized for 6 weeks without prior injection. Thus, the effect of immobilization could be evaluated additionally. Joint specimens were then examined histologically and electron microscopically.
There was clear evidence of elastase having severe destructive effects on cartilage regardless of additional joint-immobilization. In neither zero group was there prearthritic damage to the cartilage.
To prevent the initiation of cartilage damage by humoral factors, early elimination of the pathological intra-articular effusion is necessary.