The impact of lateralization and distalization shoulder angles—A systematic review of range of motion and clinical outcomes following reverse shoulder arthroplasty

Background Due to limitations of the original Grammont reverse shoulder arthroplasty (RSA) design, there has been a shift towards more anatomical implants with greater lateralization and distalization. The lateralization shoulder angle (LSA) and distalization shoulder angle (DSA) were introduced as standardized measurements of these parameters. However, their prognostic value remains controversial. This study evaluates whether LSA and DSA are correlated with range of motion (ROM), clinical outcome scores, and complications following RSA. Methods This systematic review followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and was registered with PROSPERO. PubMed, Embase, and Scopus were searched from inception to April 29, 2024. Studies reporting association between LSA and/or DSA, and post-RSA ROM and/or clinical outcomes were included. Risk of bias was assessed using QUIPS and quality of evidence using GRADE framework. Results Twelve studies comprising 2303 subjects (mean age 71.7 years, 62.6% females) were included. LSA and DSA were significantly correlated with acromial stress, scapular spine fractures, and deltoid stiffness. Neither parameter was significantly associated with ROM or clinical outcome scores. Quality of evidence ranged from “low” to “very low.” Conclusion Although LSA and DSA are simple and reproducible measures, their prognostic value for post-RSA ROM and clinical outcomes remains inconsistent.