Long-term relation between deltoid muscle volume and clinical outcomes in a reverse shoulder arthroplasty

Abstract

BackgroundDeltoid muscle function is important in reverse shoulder arthroplasty (RSA). Concerns are raised on the resistance of the deltoid muscle against the postoperative distalization. We hypothesize that a decreased volume of the deltoid muscle is related to worse clinical outcomes after a long-term follow-up. An observational study was conducted to evaluate the relation between volume of the deltoid muscle and clinical outcomes after a long-term follow-up on RSA. MethodsEligible for inclusion was patients who underwent RSA for cuff arthropathy after minimum 3 years follow-up. Fifty-nine patients were enrolled in this study. Preoperative volume was measured on magnetic resonance imaging or computed tomography. Postoperative deltoid volume was evaluated on ultrasonography. Distalization of the humerus was measured on radiographs. Clinical outcomes were measured by the Constant-Murley Score (CMS), Oxford Shoulder Score, and range of motion. Multivariable linear regression models were used to examine the association between the deltoid volume and clinical outcomes, and between distalization and deltoid volume or clinical outcomes. ResultsThe mean follow-up period was 88.7 ± 29.1 months. Postoperative deltoid volume positively correlated with both CMS (P = .045) and abduction strength, in both operated (P = .01) and contralateral side (P < .001). No association between deltoid volume and Oxford Shoulder Score or range of motion, and no association between preoperative volume and postoperative CMS was found. The mean distalization of the humerus was 21.2 mm [95% CI: 19.4-22.9 mm]. Distalization negatively correlated with deltoid volume (P = .012) and CMS (P = .009). ConclusionsPostoperative deltoid volume correlated with clinical outcomes as measured by CMS and abduction strength after a long-term follow-up on RSA.