Articular cartilage: degeneration and osteoarthritis, repair, regeneration, and transplantation.

The degeneration of articular cartilage as part of the clinical syndrome of osteoarthritis is one of the most common causes of pain and disability in middle-aged and older people. The strong correlation between increasing age and the prevalence of osteoarthritis, and recent evidence of important age-related changes in the function of chondrocytes, suggest that age-related changes in articular cartilage can contribute to the development and progression of osteoarthritis. Although the mechanisms responsible for osteoarthritis remain poorly understood lifelong moderate use of normal joints does not increase the risk. Thus, the degeneration of normal articular cartilage is not simply the result of aging and mechanical wear. However, high-impact and torsional loads may increase the risk of degeneration of normal joints, and individuals who have an abnormal joint anatomy, joint instability, disturbances of joint or muscle innervation, or inadequate muscle strength or endurance probably have a greater risk of degenerative joint disease. Recent work has shown the potential for the restoration of an articular surface. Currently, surgeons frequently debride joints and penetrate subchondral bone as well as perform osteotomies, with the intent of decreasing symptoms and restoring or maintaining a functional articular surface. The results of these procedures vary considerably among patients. Clinical and experimental work has shown the important influence of loading and motion on the healing of articular cartilage and joints. Experimental studies have revealed that transplantation of chondrocytes and mesenchymal stem cells; use of periosteal and perichondrial grafts, synthetic matrices, and growth factors: and other methods have the potential to stimulate the formation of a new articular surface. The long-term follow-up of small series of patients has shown that the transplantation of osteochondral autologous grafts and allografts can be effective for the treatment of focal defects of articular cartilage in selected patients. Thus far, none of these methods has been shown to predictably restore a durable articular surface to an osteoarthritic joint, and it is unlikely that any one of them will be uniformly successful. Rather, the available clinical and experimental evidence indicates that future optimum methods for the restoration of articular surfaces will begin with a detailed analysis of the structural and functional abnormalities of the involved joint and the patient's expectations for future use of the joint. On the basis of this analysis, the surgeon will develop a treatment plan that potentially combines correction of mechanical abnormalities (including malalignment, instability, and intra-articular causes of mechanical dysfunction), debridement that may or may not include hunted penetration of subchondral bone, and applications of growth factors of implants that may consist of a synthetic matrix that incorporates cells or growth factors or use of transplants followed by a postoperative course of controlled loading and motion.