This is an experimental, prospective, unblinded, randomized, comparative clinical trial between patients with two types of prosthetic implants (inverted arthroplasty with medialized center of rotation vs inverted arthroplasty with lateralized center of rotation). Those male or female patients who meet the inclusion criteria will be selected to form part of one of the two randomly distributed study groups. Sample size Based on studies with similar characteristics but where lateralization is not performed with the implant but with a bone graft would require a sample size of 34 patients (17 in each group) assuming 20% losses with a Type I error of 0. 05 and a statistical power of 80% to show a difference of 10 points on the Constant scale (the minimal clinically important difference on the Constant scale for reverse arthroplasty is described as 8 points in previous comparative studies so we consider the detection of a difference of 10 to be sufficient. The minimal clinically important difference for function and strength in patients undergoing reverse shoulder arthroplasty. The final N needed would be 42 patients (21 per group). A randomization of patients will be performed to assign them to one or the other study group, which will be carried out by an independent assistant, who will generate a random sequence that will be unknown to the investigators. Each patient will be given a sealed and numbered envelope to choose from, in which the randomized group in which he/she has been included will be determined. The study will be blinded for the patient and rehabilitator but not for the surgeon.
To determine the functional outcomes, complications and muscle performance by isokinetic study of two reverse arthroplasty systems (one with medialized center of rotation and the other with lateralized center of rotation) in the treatment of rotator cuff arthropathies or irreparable cuff tears.