Hylan G-F 20 (Synvisc) is an FDA-approved hyaluronate derivative used to treat knee osteoarthritis (OA). Animal studies have shown that Synvisc can have favorable effects on cartilage when injected into joints. This study attempts to evaluate the effects of Synvisc when injected into knees of patients with knee OA by means of a specialized MRI technology (dGEMRIC).