Sarcopenia of the deltoid as an indicator of outcome following reverse total shoulder arthroplasty: a systematic review and meta-analysis.

Background: Reverse total shoulder arthroplasty (rTSA) is increasingly utilized for managing rotator cuff tear arthropathy, shoulder osteoarthritis, and proximal humerus fractures. The deltoid generates the key mechanical force after rTSA. The functional success of a rTSA is dependent on the status of the deltoid muscle. Sarcopenia, defined as age-related loss of skeletal muscle mass and function, has been linked to poor outcomes in various surgical contexts. This systematic review investigates the impact of radiologically measured deltoid sarcopenia on functional and patient-reported outcomes following rTSA. Methods: A systematic search of MEDLINE, PUBMED, and SCOPUS was conducted to identify studies assessing deltoid sarcopenia via radiological imaging in rTSA patients. Inclusion criteria included studies reporting both radiological measurements of the deltoid and functional or patient-reported outcome measures. Risk of bias was assessed using the Newcastle-Ottawa Scale and the Methodological Index for Nonrandomized Studies. Results: Fourteen studies comprising 1,681 shoulders were included. Studies ranged from 2010 to 2024. Eight studies used a prosthesis based on the Grammont concept design, four studies used a reduced neck shaft angle of 135°, and two studies in which the prosthesis was not stated. Radiological modalities included magnetic resonance imaging, Computed Tomography, ultrasound, and X-ray, with deltoid cross-sectional area being the most frequently measured parameter. Meta-analysis revealed a weak, nonsignificant association between preoperative deltoid cross-sectional area and postoperative Constant-Murley Score (r = 0.12, P = .702) but a moderate positive association with postoperative muscle strength (r = 0.38, P < .001). Deltoid sarcopenia, particularly fatty infiltration and reduced muscle caliber, was associated with poorer outcomes, including lower Constant-Murley Score, reduced strength, and diminished patient-reported outcome measures. Conclusion: Radiological evidence of deltoid sarcopenia correlates with suboptimal functional and patient-reported outcomes after rTSA, the pooled effects of which are not statistically significant. However, methodological heterogeneity and inconsistent use of sarcopenia metrics limit the generalizability of these findings. Standardized imaging protocols and sarcopenia definitions are essential for improving predictive accuracy and guiding clinical decision-making.