Changes in Deltoid Muscle Tension After Reverse Shoulder Arthroplasty as Quantified by Shear Wave Elastography: Relationship with Radiographic Parameters and Functional Outcomes

Abstract Introduction Implantation of a reverse shoulder arthroplasty (RSA) impacts deltoid length, shape and tension. Quantification of changes in deltoid muscle tension with implantation of RSA has remained elusive. The purpose of this study was to use shear wave elastography (SWE) to quantify deltoid muscle stiffness preoperatively, intraoperatively and postoperatively in patients undergoing RSA. Methods Twenty patients scheduled to undergo RSA (ReUnion, Stryker) were prospectively enrolled in this study. A single observer trained in SWE quantified deltoid stiffness preoperatively, intraoperatively, and postoperatively. Clinical evaluation included pain, motion, quickDASH, ASES, Oxford, and subjective shoulder value scores. Preoperative and postoperative radiographs were measured by an independent observer to determine the lateralization and distalization shoulder angles (LSA and DSA). A statistical analysis was then performed to determine whether changes in deltoid muscle stiffness correlated with any of these parameters. Results Implantation of a RSA lead to an increase SWE deltoid stiffness value from 22.4 ± 4.2 kPa preoperatively to 29.9 ± 5.23 kPa (P˂ .0001) immediately after surgery, and 26.6 ± 6.6kPa (P= .03) at most recent follow-up. Preoperative SWE deltoid stiffness values did not differ when measured in the office or under anesthesia. Reverse arthroplasty did not significantly change the LSA (P= .051), but did increase the DSA (P Conclusion After implantation of one RSA design incorporating glenoid and humeral lateralization, deltoid stiffness as measured with SWE increased significantly. Deltoid stiffness seems to correlate with joint distalization, elevation and external rotation. SWE seems to be reliable to quantify deltoid stiffness after reverse shoulder arthroplasty. Level of Evidence Level IV; Diagnostic Study