Preoperative MRI subacromial-subdeltoid bursal thickness and pain severity in patients undergoing arthroscopic rotator cuff repair: a retrospective cross-sectional analysis

Abstract Background Pain severity in rotator cuff tears frequently diverges from structural tear dimensions. The subacromial-subdeltoid (SASD) bursa is biologically active in rotator cuff disease, but whether non-contrast MRI-measured bursal thickness is independently associated with preoperative pain intensity remains unclear. Methods This single-center retrospective cross-sectional study included 153 consecutive patients who underwent arthroscopic rotator cuff repair between August 10, 2023, and February 1, 2024. SASD bursal thickness was measured on preoperative 3.0-T fluid-sensitive MRI by two blinded musculoskeletal radiologists. Exact continuous measurements were used for all primary analyses and were available for every analysed patient, including 37 whose original clinical report recorded only “>3 mm” and whose exact values were recovered at a blinded re-read. Primary outcomes were the preoperative visual analogue scale (VAS) pain score and severe pain (VAS > = 7). Multivariable linear and logistic regressions were evaluated across three chronologically nested adjustment sets (Model A: pre-imaging demographics; Model B [primary]: Model A + preoperative range of motion; Model C [explanatory]: Model B + arthroscopic findings). Model robustness was tested using bootstrap resampling, robust M-estimation, ordinal logistic regression, and influential observation exclusion (Cook’s distance > 4/n); discrimination was evaluated with bootstrap optimism correction and repeated cross-validation. Results Of 153 consecutive records, 148 met primary inclusion criteria (5 excluded for uninterpretable MRI) and 144 had complete multivariable covariate data. Median age was 63.0 years [IQR: 52.0 to 70.0], 84 patients (56.8%) were female, median bursal thickness was 1.5 mm [IQR: 1.0 to 3.0], and 74 (50.0%) reported severe pain. Bursal thickness correlated positively with VAS pain (Spearman rho = 0.353, P < 0.001). In the primary multivariable model (Model B, n = 144), each 1-mm increment in bursal thickness was independently associated with a 0.286-point increase in VAS score (95% CI: 0.074 to 0.498, P = 0.009) and higher odds of severe pain (adjusted odds ratio [aOR] = 1.61, 95% CI: 1.20 to 2.16, P = 0.001). Effect estimates remained stable across nested adjustment sets (Model A: beta = 0.314, aOR = 1.57; Model C: beta = 0.294, aOR = 1.62) and under bootstrap resampling (bias-corrected 95% CI: 0.004 to 0.528), robust regression (beta = 0.259, P = 0.001), ordinal modeling (aOR = 1.48, P < 0.001), and exclusion of 8 influential points (beta = 0.271, P < 0.001). Adding bursal thickness to clinical variables shifted the apparent area under the curve (AUC) from 0.743 to 0.793 (DeLong P = 0.040), yielding an optimism-corrected AUC of 0.742 (calibration slope = 0.75). Conclusion Preoperative MRI-measured SASD bursal thickness is independently associated with preoperative pain severity in patients undergoing arthroscopic rotator cuff repair, showing high consistency across adjustment sets and modeling assumptions. Given the surgical selection context, moderate multivariable overfitting, and the absence of a validated cutoff, bursal thickness is best characterized as a continuous imaging correlate of preoperative pain burden rather than a predictive instrument.