Patients recruited at selected sites will be extended the opportunity to participate in a trial that administers blinded study agents for a total of 24 months. This study is a preliminary evaluation of whether glucosamine, chondroitin sulfate and/or the combination of glucosamine and chondroitin sulfate are more effective than placebo and whether the combination is more effective than glucosamine or chondroitin sulfate alone in altering radiographic progression in patients with osteoarthritis (OA) of the knee after two years of follow-up.