JSES - 2026-05-01 - Journal Article
The impact of rotator cuff muscle volume on functional outcomes following reverse total shoulder arthroplasty: the use of a validated muscle segmentation software.
Werthel JD, Bowler AR, Vervaecke AJ, Diestel DR, Arnold RP, McDonald-Stahl M, Jawa A
Topics
Key Takeaway
Normalized rotator cuff muscle volume showed no significant correlation with functional outcomes or ROM after rTSA in either OA or CTA patients across 528 cases at mean 29.1 months follow-up.
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Summary
This study asked whether preoperative rotator cuff muscle volume, quantified via validated CT segmentation software, predicts functional outcomes after rTSA in OA versus CTA patients. CTA patients had significantly lower normalized supraspinatus, infraspinatus, and subscapularis volumes and higher intramuscular fat across all four cuff muscles compared to OA patients (P<.001), yet neither muscle volume nor intramuscular fat correlated with postoperative ASES, SSV, VAS, or active ROM in either group. The only notable correlation was a moderate negative relationship between deltoid intramuscular fat and preoperative ASES (r=-0.43) and VAS (r=0.43) in the CTA cohort, which did not persist postoperatively.
Key Limitation
The retrospective single-institution design with a short mean follow-up of 29.1 months may not capture late functional changes driven by progressive muscle atrophy or fatty infiltration after rTSA.
Original Abstract
BACKGROUND
The indications for reverse total shoulder arthroplasty (rTSA) have progressively expanded, and it is now implanted for a wide range of clinical scenarios, including cases with an intact rotator cuff. The objective of this study was to use a validated computed tomography (CT) muscle segmentation software to evaluate the relationship of rotator cuff muscle volume and postoperative clinical outcomes.
MATERIALS AND METHODS
A retrospective study was conducted using an institutional database including all patients who underwent rTSA between 2016 and 2022, with a minimum of two years of follow-up. Patients were divided into 2 groups based on the indication: centered osteoarthritis (OA) and cuff tear arthropathy (CTA). Clinical outcomes were assessed preoperatively and postoperatively, including active range of motion (ROM), American Shoulder and Elbow Surgeons score, Subjective Shoulder Value, and visual analog scale for pain. Preoperative CT scans were automatically segmented with a validated CT muscle segmentation software to isolate the scapula, humerus, deltoid, and the 4 rotator cuff muscles. Muscle volume and the percentage of intramuscular fat were measured and normalized to scapular volume. Statistical analyses were performed to investigate correlations between muscle volume, functional outcomes, and ROM.
RESULTS
A total of 528 patients (460 OA, 68 CTA) with an average follow-up of 29.1 ± 8.6 months were included. Normalized muscle volume of the supraspinatus, infraspinatus, and subscapularis was significantly greater in OA patients than in CTA patients (P < .001). No significant differences were observed for the deltoid (P = .92) or teres minor (P = .81). The percentage of intramuscular fat was significantly higher in the supraspinatus, infraspinatus, teres minor, and subscapularis in CTA patients compared to OA patients (P < .001). No significant difference was observed for the deltoid (P = .97). No significant correlation was found between normalized muscle volume (cuff or deltoid) and functional scores or active ROM, either preoperatively or postoperatively following rTSA. In the CTA cohort, a moderate negative correlation was observed between deltoid intramuscular fat percentage and preoperative American Shoulder and Elbow Surgeons score (r = -0.43; P = .031) and preoperative visual analog scale (r = 0.43; P = .026). No correlation was found between intramuscular fat percentage (cuff and deltoid) and postoperative functional outcomes or active ROM.
CONCLUSION
rTSA for OA achieves better outcomes than rTSA for CTA. The difference in outcomes showed no correlation with muscle volumes, indicating that rotator cuff muscles may play a less critical role in functional outcomes after rTSA than previously thought.