Experimental hemijoint and whole-joint transplantation.

Technically perfect autologous hemijoint transplants maintain biologic viability, although gradual deterioration of the joint surface may occur with the passage of long periods. Allogeneic transplants demonstrate varying degrees of degeneration, depending on the circumstances surrounding the procedure. Fresh allografts with a large amount of subchondral bone are rapidly rejected, with an immune response directed against both bony and cartilaginous components. Frozen allografts with a small amount of subchondral bone usually maintain the overall joint configuration for some time but then degenerate. In many instances the role of the immune system in rejection of joint transplants is difficult to define. The fate of whole nonvascularized knee joint transplants is comparable with that of hemitransplants. Although fresh autografts give the best results, the subchondral bone can collapse, and articular cartilage degenerates in some cases. Recent investigations of immediately revascularized canine whole knee transplants show that when the blood supply is maintained to the autograft, normal biologic function is sustained for as long as five years after grafting. When appropriate immunosuppression is used, successfully revascularized allografts survived for as long as 18 months. However, bony and cartilaginous necrosis occurs in focal areas. In any case, successfully revascularized osteochondral grafts are biologically superior to nonvascularized grafts.