Abstract
INTRODUCTION: Reverse shoulder arthroplasty (RSA) is performed for various shoulder pathologies. Inadequate tensioning of the deltoid muscle can lead to complications, highlighting the need for optimization. Preoperative quantification of deltoid health may improve operative execution and outcomes. Shear wave elastography (SWE) quantifies stiffness as a marker for muscle health and tensioning. This study establishes normal reference values for the deltoid in healthy individuals. METHODS: 40 participants were enrolled, 10 in each 18-30, 31-40, 41-55, and 55 + age groups. Two operators performed SWE in 3 deltoid regions, and the intra- and inter-operator agreement was assessed. RESULTS: Mean values were 23.2 ± 4.6, 26.4 ± 5.6, and 17.9 ± 5.2 kPa for the anterior, lateral, and posterior regions. The posterior region did not show any age dependency. However, there were significant differences between the age groups of 18-30 and 55 + years in the anterior (19.7 ± 3.7 vs. 26.7 ± 5.3 kPa) and lateral (22.0 ± 5.4 vs. 30.2 ± 8.8 kPa). Intra-operator reliability ranged from 0.45 to 0.60, and inter-reader agreement from 0.57 to 0.85. CONCLUSION: This study provides reference values of deltoid stiffness which could serve as a comparison with clinical measurements for RSA operative planning and execution and prediction of surgical outcomes.