Different treatment options are available for massive or irreparable rotator cuff tears. An arthroscopic or an open repair approach is possible in the majority of cases and functional outcomes are improved, particularly when a complete arthroscopic repair can be achieved. However, the healing rate of massive rotator cuff tears after repair may remain low and failure of healing is associated with progression of arthritis. An alternative to arthroscopic or open repair is reverse shoulder arthroplasty which decreases pain and improves function, active shoulder elevation and quality of life. The primary goal of this prospective multicentric randomized study is to determine if there is a difference of functional outcomes between rotator cuff repair (RCR) repair and reverse shoulder arthroplasty (RSA).