A new procedure for regenerating damaged articular cartilage in the knee joint to relieve the pain of osteoarthritis is being studied by Rush University Medical Center. Rush is the only center participating in the CAIS Phase III clinical trial in Illinois. Cartilage Autograft Implantation System (CAIS) is a procedure that involves extracting cartilage from the healthy tissue that remains in the knee, breaking it into tiny fragments to enable it to grow and expand, fixing it onto a biologically reabsorbable scaffold, and then implanting the scaffold with the cartilage cells back into the damaged area all in a single surgery. Unlike the most popular surgical treatment currently for regenerating cartilage, called microfracture, earlier laboratory studies at Rush had indicated that the procedure can yield the tougher hyaline cartilage that naturally occurs in the joint. After a pilot study in 2006 demonstrated the procedure was safe, almost 40 centers in North America have come up to participate in the clinical trial. The investigators are now aiming to determine whether the procedure is as at least effective as microfracture, and possibly better. Approximately 300 patients will be participating in the trial, including both men and women ages 18 to 65 who have one or two lesions in their knee, but not significant arthritis that might require a knee replacement. The follow up of participants will be for 48 months. Results will be compared with outcomes for microfracture, in which the surgeon creates tiny fractures in the bone underlying the damaged cartilage with a tiny pick-like tool. Blood and marrow, which contains stem cells, leak out of the fractures, forming a blood clot with cartilage-building cells. But studies have shown that microfracture is not always the ideal treatment.