Current treatment options for the restoration of articular cartilage.

Over the past several decades, much has been learned about articular cartilage and its physiological capacity to restore itself. While articular cartilage does appear to have some regenerative capabilities, it appears to lose this capacity over a period of time, making restoration of articular surfaces more and more difficult. To date, no technique has been completely successful in achieving exactly normal regenerative articular cartilage. Arthroscopic lavage and debridement provides temporary relief of symptoms. This probably works by removing degradative enzymes that contribute to synovitis and also to the further breakdown of articular cartilage. Bone marrow stimulation techniques such as abrasion arthroplasty, drilling, and microfracture produce only fibrocartilage and therefore do not offer a long-term cure. Perichondral and periosteal interposition grafts produce repair tissue that is similar to hyaline cartilage but also lack the mechanical durability. Like bone marrow stimulation techniques, interposition grafts introduce precursor cells, which have a tendency to differentiate along lines other than cartilage. This leads to an inferior quality of repair tissue. Currently, chondrogenic-stimulating factors and artificial matrices are currently being researched and developed. Much has been learned about the various growth factors that stimulate chondrocyte differentiation and extracellular matrix production, but to date, there has not been a clinical technique that has shown any long-term promise. Ultimately, the goal will be to take precursor cells from an easily accessible source such as the iliac crest, mix them with growth factors that have been derived genetically in the lab, and provide an artificial matrix that in combination can produce restoration of articular cartilage at minimal cost and patient morbidity. Autologous osteochondral transplant systems have shown encouraging results but there are still problems. Graft matching and contouring to the recipient articular surface is difficult. Donor sites can be a limiting factor. Furthermore, the fibrocartilaginous interface between the donor and recipient site may contribute to breakdown in the long run. Autologous chondrocyte implantation is a biological repair process that also has shown encouraging results. It must be remembered that this is not normal articular cartilage--it is only hyaline-like cartilage. The technique is expensive and is technically difficult to perform. There are no randomized prospective studies that compare the natural history of the repair tissue to that of other forms of repair tissue. Long-term functional outcome is still a significant question mark. In addition, it has not been shown that autologous chondrocyte implantation can prevent degenerative changes. In the future, we probably will see delivery systems using stimulating growth factors, chondrocytes, and synthetically derived matrices. When placed in combination and with the right mechanical stimuli, we may ultimately achieve true restoration of articular cartilage.