Determine the optimal degree of retroversion (0-30º) to obtain the best rotational mobility, both internal and external, of the shoulder after implanting a reversed sghoulder arthroplasty (Comprehensive system), and analyze the functional and radiologic results based on humeral retroversion.

Methodology: Open randomized controlled clinical trial. It will be carried out with patients operated with reverse shoulder arthroplasty (at 0º and 30º of humeral retroversion) included consecutively in Terrassa Hospital from January 2019 to June 2021. The estimated sample will be 30 patients per group with diagnosis of massive rotator cuff rupture, rotator cuff arthropaty and primary osteoarthritis with cuff injury, with Walch's type B2 glena or in patients older than 80 years. A global study will be carried out preoperatively and postoperatively with radiographs, computerized tomography, magnetic resonance, and a biomechanical study.

Inclusion Criteria:

• men and women over 60 with the diagnosis rotator cuff massive break (Hamada 2 or more), arthrosis secondary to ruptures of the rotator cuff and primary osteoarthritis with lesion of the cuff, with full Walch B2 type or in patients older than 80 years. Inclusion criteria
• Good functionality of the deltoid muscle.
• Presence of minor round (Hornblower test - no muscle atrophy in nuclear magnetic resonance)
• Accept informed consent

Exclusion Criteria:

• - Review of hemiarthroplasty or anatomical proesis of the affected shoulder.
• Fracture of shoulder in the upper extremity to intervene.
• Central neurological diseases
• Advanced cognitive impairment
• Brachial plexus injuries
• Local or systemic infection.
• Oncological disease
• Treatment with immunosuppressants.

Open randomized controlled clinical trial.