Massive irreparable rotator cuff tears are a common cause of pain and disability. Several different treatments exist;​ however, they are associated with poor clinical outcomes and survivorship in younger patients without glenohumeral arthritis. The purpose of this thesis was to compare the impact of a subacromial balloon spacer, superior capsular reconstruction, and a rigid subacromial implant on the glenohumeral kinematics and mechanical efficiency of a massive rotator cuff deficient shoulder. The results indicate that each surgical state improves the glenohumeral kinematics of a massive irreparable rotator cuff tear. The subacromial implant leads to mild overcorrection of humeral head translation. No surgical state achieves the mechanical efficiency of the intact shoulder, except for the superior capsular reconstruction at 0-degrees and the subacromial implants at 60-degrees abduction. Each surgical state appears to correct the biomechanical abnormalities of rotator cuff deficiency, each with their own unique limitations.