Eighty patients with full thickness rotator cuff tears scheduled to undergo an arthroscopic rotator cuff repair were randomized to receive an injection of atelocollagen plus hyaluronic acid (n=28), hyaluronic acid only (n=26) or no injection (n=26) after the completion of the rotator cuff repair. Outcomes of interest included pain and function on a Visual Analog Scale (VAS), the American Shoulder and Elbow Surgeons (ASES) score, range of motion (forward elevation; external rotation on the side; internal rotation at the back; abduction), the rate of retear, and the number of steroid injections. Clinical outcomes were assessed at 3, 6 and 12 months post-operation. Results revealed no significant differences in all outcomes among the three groups. However, the rate of retear and the number of steroid injections at 3 months was significantly different among the three groups, with the lowest rates being observed in the combination group.