Preoperative MRI-Derived Deltoid Morphometry and Early Pain and Functional Recovery After Arthroscopic Rotator Cuff Repair: A Size-Normalized, Segment-Specific Analysis

Abstract

The deltoid is a primary compensatory motor for shoulder elevation and may influence early recovery after rotator cuff repair. The purpose of this study was to evaluate whether preoperative magnetic resonance imaging (MRI)-derived deltoid morphometry, normalized to humeral head diameter, is associated with early postoperative function and pain after arthroscopic repair of full-thickness supraspinatus tears (± infraspinatus involvement). We hypothesized that greater size-normalized deltoid thickness—particularly posterior thickness—would be associated with superior early functional outcomes and lower pain. Cohort study; Level of evidence, 3. A retrospective cohort of 38 patients who underwent primary arthroscopic rotator cuff repair (ARCR) for full-thickness supraspinatus tears (± infraspinatus) was analyzed. Preoperative MRI was used to quantify anterior, middle, and posterior deltoid thickness, deltoid cross-sectional area (CSA), and humeral head diameter. Size-normalized indices were calculated as thickness/diameter for each deltoid segment and as (CSA/diameter 2 ). Clinical outcomes included Constant score and visual analog scale (VAS) pain assessed preoperatively and at the standardized routine 3-month postoperative follow-up; change scores were calculated as ΔConstant and ΔVAS. The mean age was 56.7 ± 6.4 years, and 60.5% of patients were women. Clinical outcomes improved significantly at the routine 3-month postoperative follow-up, with the Constant score increasing from 38.8 ± 6.7 to 51.6 ± 8.5 and the VAS pain score decreasing from 6.7 ± 1 to 3.4 ± 1.1 (both P < .001). After false discovery rate correction, posterior deltoid thickness index showed the strongest associations with early outcomes. Posterior deltoid thickness index was associated with higher 3-month postoperative Constant score ( r = 0.686 [95% CI, 0.469 to 0.825]; P < .001; Q < 0.001) and lower 3-month postoperative VAS pain ( r = −0.600 [95% CI, −0.771 to −0.346]; P < .001; Q = 0.001). In exploratory adjusted regression, posterior deltoid thickness index remained associated with 3-month postoperative Constant score and VAS pain after adjustment for age, sex, and tear size. Preoperative size-normalized, segment-specific deltoid morphometry on MRI, particularly posterior deltoid thickness, may be associated with early pain and functional recovery after ARCR. These exploratory findings require prospective validation before clinical use.