Pre-operative deltoid fatty infiltration as a predictor of outcomes after reverse total shoulder arthroplasty: a systematic review.

Background: Reverse total shoulder arthroplasty (rTSA) has become an increasingly common surgery to address various pathologies of the shoulder. The deltoid muscle is the primary driver for shoulder movement following rTSA, and its functionality is integral to rTSA outcomes. The aim of this systematic review was to investigate the impact of pre-operative deltoid fatty infiltration, as seen and quantified through imaging or by the Goutallier classification, on post-operative outcomes following rTSA. Methods: A systematic review was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A PubMed and Google Scholar search using the following search terms: "deltoid," "fatty infiltration," and "shoulder arthroplasty" was performed. The literature search aimed to identify studies that measured deltoid fatty infiltration and evaluated post-operative outcomes through clinical assessments. One thousand seven hundred sixty-three papers were analyzed and narrowed down for the focus of this review. Inclusion criteria included relevance, quality of research, significance of findings, and number of citations. Results: Five papers met the inclusion criteria and were included in the review. The results of these papers were summarized. All of these papers were retrospective cohort studies. Higher levels of pre-operative deltoid fatty infiltration, measured by computed tomography, magnetic resonance imaging, or quantified by Goutallier classification, were associated with poorer post-operative rTSA outcomes. This was confirmed through clinical and functional assessments including American Shoulder and Elbow Surgeons, Constant Murley score, Shoulder Arthroplasty Smart score, and Korean Shoulder Scoring System. An association between lower assessment scores and higher levels of deltoid fatty infiltration proved positive in all the studies. Conclusion: The health of the deltoid muscle is integral to post-operative rTSA outcomes; the amount of fatty infiltration of the deltoid is one potential predictive measure of post-operative clinical outcomes. It is necessary for orthopedic surgeons to be aware of the impact of deltoid fatty infiltration in order to optimize rTSA outcomes for their patients.