Understanding loss of internal rotation after reverse shoulder arthroplasty: a narrative review of current literature.

Background: Functional internal rotation (fIR) can be limited after reverse shoulder arthroplasty (RSA) and can result in difficulties performing activities of daily living (ADLs). The goal of this narrative review is to summarize the growing body of research on optimizing fIR after RSA that may be useful to clinical practice. Methods: A narrative review of recent literature on IR after RSA. Results: IR required for ADLs is a compound motion involving multiple joints and planes; for this reason, the term "functional internal rotation" can be used to differentiate this motion from glenohumeral IR. Measuring IR by vertebral level is limited by interobserver reliability and poor correlation with the ability to perform ADLs. IR-specific scores or questions may be more relevant. Patient-based factors that influence IR include body mass index, thoracic spine sagittal alignment, humeral torsion, preoperative humerothoracic extension, and scapulothoracic mobility. Surgically, a healed subscapularis repair appears to improve IR and anterior latissimus dorsi transfers have been described with favorable results. Tools to predict IR after RSA are emerging and may be helpful to counseling patients on implant selection. Conclusion: FIR after RSA is optimized by maximizing impingement-free arc of motion and subscapularis repair in patients with mobile scapulothoracic joints, adequate preoperative humerothoracic extension, and low body mass index.