Reliability and validity of a new deltoid muscle area measurement method after reverse shoulder arthroplasty

Katsumasa Nakazawa; Tomoya Manaka; Yoshihiro Hirakawa; Yoichi Ito; Ryosuke Iio; Naoki Oi; Hiroaki Nakamura

doi:10.1016/j.jseint.2023.08.002

Reliability and validity of a new deltoid muscle area measurement method after reverse shoulder arthroplasty

JSES Int. 2023 Sep 3;7(6):2500-2506. doi: 10.1016/j.jseint.2023.08.002. eCollection 2023 Nov.

Authors

Katsumasa Nakazawa¹, Tomoya Manaka¹, Yoshihiro Hirakawa², Yoichi Ito³, Ryosuke Iio¹, Naoki Oi³, Hiroaki Nakamura¹

Affiliations

¹ Department of Orthopaedic Surgery, Osaka City University Graduate School of Medicine, Osaka, Japan.
² Department of Orthopaedic Surgery, Ishikiriseiki Hospital, Higashiosaka, Japan.
³ Osaka Shoulder Center, Ito Clinic, Osaka, Japan.

Abstract

Background: Accurate deltoid muscle assessment after reverse shoulder arthroplasty (RSA) is difficult using magnetic resonance imaging due to metal artifacts. We hypothesized that measuring the deltoid muscle area (DA) in the middle part of the deltoid's total length postoperatively would reduce metal artifacts and allow for an accurate assessment. This study aimed to assess the reliability and reproducibility of magnetic resonance imaging and evaluate its impact on postoperative outcomes.

Methods: The DA in the middle part of the muscle's total length was measured twice by four examiners using pre and postoperative magnetic resonance imaging in 60 patients who underwent RSA (22 men, 38 women; mean age: 77.4 years). The DA at the greater tuberosity was measured preoperatively, and its correlation with the middle part of the deltoid's total length was evaluated. The Constant-Murley Score was measured at 2 years postoperatively, and its correlation with the DA in the middle part of the deltoid's total length pre- and postoperatively was assessed.

Results: Intraclass correlation coefficients for intraobserver measurements of preoperative and postoperative DA in the middle part of the deltoid's total length were almost perfect, with mean values of 0.98 and 0.97, respectively. The intraclass correlation coefficients for interobserver reliability regarding the first and second DA measurements in the middle part of the deltoid's total length were 0.95 and 0.95 (preoperatively) and 0.89 and 0.90 (postoperatively). The Constant-Murley Score was assessed at 2 years postoperatively in 51 patients. Muscle strength was weakly and moderately correlated with preoperative DA (r = 0.33, P = .02) and postoperative DA (r = 0.49, P < .01), respectively.

Conclusion: DA measurement in the middle part of the deltoid's total length after RSA was not affected by metal artifacts and had excellent reproducibility. This measurement method positively correlated with postoperative muscle strength, suggesting its usefulness for predicting postoperative muscle strength.

Keywords: Constant–Murley Score; Cuff tear; Deltoid muscle area; Metal artifacts; Muscle strength; Reverse shoulder arthroplasty.