Determination of Scapulothoracic and Glenohumeral Angles by Imaging in Patients After Shoulder Arthroplasty (SCAP-imag)

The shoulder is a site particularly affected by osteoarthritis since it affects up to 7% of the population aged over 65. To deal with osteoarthritis, total shoulder prosthesis is an increasingly used solution. Among the different types of total shoulder prostheses, the majority of surgical procedures involve the use of a reverse total shoulder prosthesis. This type of prosthesis modifies the anatomy of the shoulder in order to ensure better stability and mobility of the shoulder in patients while also compensating for potential significant lesions of certain deep muscles of the shoulder joint (i.e., rotator cuff). Reverse prostheses have good short-term results but these are impaired in longer term with a Constant functional score of around 70% at 10 years and a survival rate of 70% after 20 years. Problems of bone conflicts between the scapula and the humerus can also be observed on these reverse total shoulder prostheses with variable rates from 4.6% to 47.3% depending on the position of the prosthesis. In order to minimize the risk of complications, several tools are available to surgeons to optimize the positioning of the prosthesis. Planning software can be used to plan the kinematics of the shoulder after arthroplasty and quantify shoulder movements by 1/ estimating the scapulothoracic and glenohumeral angles, and 2/ determining the scapulohumeral rhythm (i.e., joint coordination index evaluating the relative contribution of these two joints to the total elevation of the arm). This prediction allows the surgeon to adapt the size, shape and position of the implants to each patient in order to ensure optimal shoulder kinematics, namely a maximum amplitude without bone conflicts (contacts) between the scapula and the humerus. The main objective of this study is to evaluate the influence of a reverse shoulder arthroplasty on shoulder kinematics at 2 years postoperatively in comparison with the non-operated contralateral limb.