Reverse Total Shoulder Arthroplasty: The Impact of Implant Design on Postoperative Internal Rotation

Abstract

Abstract Title: Reverse Total Shoulder Arthroplasty: The Impact of Implant Design on Postoperative Internal Rotation Background Reverse total shoulder arthroplasty (rTSA) is a ubiquitous surgical procedure indicated for numerous glenohumeral pathologies. Repeated evidence demonstrates its efficacy in improving shoulder function and reducing pain; however, improvements in rotational motion have been inconsistent. Attention has recently shifted toward internal rotation (IR) as an important component of activities of daily living (ADL). Subsequently, IR has been strongly associated with post-operative patient satisfaction. To date, there has been little discussion regarding implant design on IR. As the community shifts toward more lateralized center-of-rotation and varus humeral implants, it is unclear how this will impact rotational motion. Methods A systematic review was performed following PRISMA guidelines. Search strategies were implemented in PubMed with the keywords (internal rotation) AND (reverse) AND (shoulder). Inclusion criteria included a minimum 12-month follow-up, reporting of IR, and implant description. Exclusion criteria included rTSA solely for proximal humerus fractures, oncologic reconstruction, or severe glenoid deformity, revision rTSA, and procedures including latissimus dorsi or tendon transfers. After review, 56 studies from 332 unique citations were selected. Results Analysis was performed on 56 studies consisting of 7788 shoulders treated with rTSA at a mean follow-up of 42.4 months. IR was reported for 7288 shoulders (94%). Measurement systems were highly heterogeneous necessitating conversion to a common metric. This permitted comparative analysis of 46 studies encompassing 6123 shoulders (79%). Varus (135°) humeral implant neck shaft angles (NSA) were associated with the greatest post-operative IR, though intermediate (145-147°) and valgus (150-155°) NSA produced comparable results. Varus and intermediate NSA outperformed valgus NSA in terms of mean change in IR. Accounting for humeral NSA, lateralized glenospheres resulted in greater post-operative IR. When classifying implant systems with the Werthel global offset system, highly lateralized and very highly lateralized systems produced greater post-operative IR than medialized systems. Conclusion The results of this systematic review indicate that lateralization of the center-of-rotation and varus humeral NSA optimize IR. A classic Grammont-style rTSA, a medialized center-of-rotation with a valgus NSA, was associated with predictably poor IR. This review suggests trends toward lateralized center of rotation and varus NSA will result in improved IR.