360 patients with knee osteoarthritis were randomized to one of four groups: combined intra-articular platelet-rich plasma and hyaluronic acid injection, intra-articular platelet-rich plasma injection alone, intra-articular hyaluronic acid injection alone, or intra-articular placebo injection. Patients were assessed for the primary outcome measure of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score over 52-week follow-up. Reduction in WOMAC pain and functional disability scores from baseline to 52 weeks were significantly greater in the combined PRP+HA group compared to either PRP or HA alone, though reduction relative to the placebo group was not reported.