PURPOSE: To synthesize and report the early clinical and radiographic outcomes associated with subacromial spacer use in patients with massive irreparable rotator cuff tears. METHODS: A systematic search on MEDLINE, Embase, and Cochrane Library databases was performed during February 2018. Included studies were evaluated regarding the level of evidence and quality using the methodological index for nonrandomized studies. Patient demographics, intraoperative findings, clinical and radiographic outcomes, and complications were recorded for each of the included studies. RESULTS: Seven eligible studies including 204 shoulders from 200 patients with subacromial spacer implantation were identified (6 Level IV studies and 1 Level III study). The mean methodological index for nonrandomized studies score for noncomparative studies was 11, whereas that of comparative studies was 15. The mean age of patients was 67.6 years, and the mean reported follow-up time was 19.4 months. All patients had Goutallier stage 3 and 4 fatty infiltration on magnetic resonance imaging. All studies reported consistent improvement in the total Constant score or American Shoulder and Elbow Surgeons score over the duration of follow-up. A total of 6 (3%) complications were reported in the included studies. Two studies detailed radiographic outcomes, with discrepant changes in the acromiohumeral interval. CONCLUSIONS: Patients undergoing subacromial spacer implantation for the treatment of massive irreparable rotator cuff tears have satisfactory outcomes at the 2- to 3-year follow-up with a low rate of complications. LEVEL OF EVIDENCE: Level IV, systematic review of 1 Level III and 6 Level IV studies.