Deltoid Muscle Volume Correlates With Patient Outcome After Reverse Shoulder Arthroplasty

Reverse total shoulder arthroplasty (rTSA) relies on a competent deltoid muscle to provide stability and function. This study aims to determine the importance of ultrasonically measured deltoid muscle volume on patient strength, function, and satisfaction after rTSA.

We retrospectively reviewed 56 shoulders in 28 patients underwent rTSA with surveys of American Shoulder and Elbow Society questionnaire (ASES), simple shoulder test, and ultrasonography measurement of deltoid volume. Statistical analysis was done to determine the correlation between deltoid muscle volume and abduction strength, ASES score, Constant-Murley Score, Visual Analog Scale, range-of-motion testing, between surgical shoulder and nonsurgical repair groups, respectively.

A strong positive correlation was observed with deltoid muscle volume and abduction strength, and a moderate positive correlation between deltoid muscle volume and the Constant-Murley Score. No notable difference was observed between the mean deltoid volume for the surgical and nonsurgical sides. No correlation existed between deltoid volume and ASES. A decrease in deltoid muscle volume was observed with patients' age, but no trend regarding length of time since surgery. These findings indicated that deltoid muscle assessment in candidate selection and postoperative care are associated with improved postoperative outcomes.

Deltoid volume is a robust predictor of postoperative abduction strength and has a moderate association with shoulder function including muscle strength and range of motion but does not correlate with pain or satisfaction. The results can inform clinicians to prioritize deltoid evaluation during patient selection and follow-up, guiding additional research on optimizing rehabilitation and implant design.

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