The investigators are an orthopaedic clinic in Zurich (Universitätsklinik Balgrist, Zürich) with about 250 arthroscopic rotator cuff repairs per year. Our plan is to recruit at least 100 participants in a year for this prospective clinical study. The participants have to fulfill the inclusion criterions. The diagnosis for the rotator cuff tears are made on the basis of arthro-MRI scans. The investigators do the operations in our clinic. The entire follow-up is one year for each participant. We plan three regular postoperative consultations. The tendon healing is controlled postoperative by ultrasound (six weeks and 4 month postoperative) and by MRI (one year postoperative).