The impact of glenoid/humeral lateralization and distalization angles based in the pattern of reverse shoulder arthroplasty

Abstract

Background

The biomechanics of reverse shoulder arthroplasty (RSA) rely on deltoid function. The center of rotation of the glenohumeral joint in RSA is more medial and distal when compared to the native joint, and proper soft-tissue tensioning is essential to achieve a stable joint with a good range of motion (ROM). The current RSA systems on the market allow for various placements of humeral and glenoid components (lateralized, medialized, distalized). No post-operative radiographic parameters currently consider the glenoid and humeral components' position separately. The aims of this study are to (1) measure glenoid and humeral component angles specific to different implants and (2) to investigate whether these angles correlate with clinical outcomes.

Methods

A retrospective analysis of 74 patients who underwent reverse shoulder prosthesis between 2018 and 2022 was performed. Different subtypes of RSA prosthesis were identified (medialized glenoid/lateralized humerus, lateralized glenoid/medialized humerus, and lateralized glenoid/lateralized humerus). Angle measurements were defined to determine the lateralization and distalization of each component in true anteroposterior radiographs (Grashey view) of the shoulder. The clinical results were collected, including a Simple Shoulder est, Single Assessment Numeric Evaluation, and Constant score.

Results

All angles showed excellent intra-rater and inter-rater agreement. No correlation was found between ROM and post-operative radiographic measurements, and there were no significant differences between the different RSA subtypes in clinical outcomes.

Conclusion

The main objectives to be met are the post-operative scores, ROM, and patient satisfaction after RSA; however, there are still no reliable measures in post-operative radiographs that correlate with clinical outcomes. The current angles obtained on post-operative radiographs allow us to assess the prosthesis's placement degree due to each of the components but not to predict ROM or clinical outcomes.