Intraarticular HA or PRP has been used for knee OA for years. Combined HA and PRP has not been widely used for OA because of lack of clinical evidence. Based on in vitro and animal studies, combining HA and PRP may benefit from their dissimilar biological mechanisms for tissue repair and have potentials to synergistically promote cartilage regeneration, inhibit OA inflammation, modulate the disease process, and improve joint homeostasis in OA. Combination of HA and PRP has much potential for the treatment of OA, but the clinical evidence of this combination remains unclear. The purpose of this study was to investigate the efficacy and safety of combined a single crosslinked HA (HYAJOINT Plus) with a single PRP versus a single PRP alone in patients with knee OA.