Limited range-of-motion (ROM) is a common problem after reverse shoulder arthroplasty (RSA). The occurrence and magnitude depend on both surgical and patient-related factors. The most important surgical factor is the occurrence of impingement, which implicates collision between the humeral implant or bone and the scapula, limiting further motion. Patient-related factors such as scapula geometry and muscle function and activation also play an important role. Surgeons have to account for these factors when planning and implanting a RSA. Software models can support the surgeon during preoperative planning by using imaging data to simulate the ROM of a patient's shoulder after RSA. These software models allow for adaptation of the implant position during preoperative planning and, by this optimize the postoperative ROM. However, the models currently developed are limited in terms of ROM simulation and the factors the models take into account.

The impingement-free ROM in a RSA patient is defined as the rotational area the humeral liner can move through without colliding against the scapula or dislocating the joint. In a previous study, a new software model was developed that uses imaging data to compute and quantify the impingement-free ROM of a patient according to clinically relevant motions. Before this model can be used in clinical practice, a validation of the model's accuracy in predicting real RSA patient outcomes is required. Therefore, the first objective is to verify the model's ability to predict the ROM of the glenohumeral joint in real RSA patients. The investigators will investigate and quantify the ROM and joint angles of RSA patients with and without impingement with the help of EOS imaging and video motion analysis. The investigators can then compare model outputs with measured patient outcomes. Additionally, the investigators will investigate how well our software model can predict impingement in patients with known postoperative impingement.

Currently, the software model uses a database of healthy shoulder kinematic motions to produce an objective ROM score for a RSA. However, it is not known if healthy shoulder kinematics are a suitable reference for quantifying and interpreting RSA kinematics. Glenohumeral motions of healthy subjects are already extensively described by Ludewig et al. Glenohumeral motions of RSA patients are not yet reported. Also, little is known about muscle activation patterns in RSA patients. The second objective is to describe muscle activation patterns and shoulder kinematics of RSA patients and compare our measured RSA kinematic motions to the healthy kinematic motion data currently used in the software model. Therefore, the investigators will perform instrumented 3D motion analysis in conjunction with electromyography measurements to incorporate muscle activation patterns into our RSA glenohumeral motion analysis. Our additional sub-objective is to compare muscle activation patterns between patients with and without limited ROM, with the goal of identifying differences between the two groups.

The third objective is to identify patient-related and implant related factors that influence the ROM after a reversed shoulder arthroplasty. Therefore, the investigators will investigate clinical factors that could have effect on the ROM after RSA. The different factors (sex, birth year, Body Mass Index, generic score EQ-5D-3L, Tampa Schaal voor kinesofobia) will be analyzed both across and within patients with and without limited ROM with the goal of identifying their relation to ROM. The most important implanted related factor will also be investigated and analyzed both across and within groups: implant position in terms of glenoid component version, inclination and location of center of rotation.

Inclusion Criteria:

• Adults with RSA operated in the University Hospitals Leuven, Belgium
• Ability and willingness of patient to attend follow-up visit and complete patient questionnaires
• Complete patient informed consent
• Preoperative CT-scan available
• Pain free RSA (VAS score ≤ 3) more than 1 year postoperative

Exclusion Criteria:

• Only RSA patients with a functional RSA will be included, so patients with postoperative stiffness, pain, instability or pseudoparalysis will be excluded.