Association between preoperative MRI-measured membranous urethral length and early urinary continence recovery after robot-assisted radical prostatectomy: a retrospective cohort study

Background Robot-assisted radical prostatectomy (RARP) is a key surgical approach for localized prostate cancer, yet early postoperative urinary incontinence remains a major functional concern. Membranous urethral length (MUL), measurable by preoperative MRI, may predict continence recovery, but its relationship with early outcomes warrants further clarification. Objective To investigate the association between preoperative MRI-measured MUL and early complete urinary continence recovery after RARP, and to evaluate its dose-response relationship and discriminative ability. Methods This retrospective cohort study included 152 patients who underwent RARP (October 2024–March 2026). MUL was measured on preoperative T2-weighted MRI by two independent observers. Urinary continence (0 pads/day) was assessed at 1 and 3 months after catheter removal. Multivariable Logistic regression (1 month) and Firth penalized Logistic regression (3 months) were used. Restricted cubic spline, ROC curves, and propensity score matching were performed. Results Median MUL was 13.49 mm. Interobserver agreement was excellent (ICC = 0.946). Complete continence recovery rates at 1 and 3 months were 51.32% and 79.61%, respectively. Each 1-mm MUL increase was independently associated with higher odds of continence recovery at 1 month (OR = 1.758, 95% CI: 1.450–2.132, P<0.001) and 3 months (OR = 1.502, 95% CI: 1.247–1.809, P<0.001). Older age and higher BMI were associated with lower odds of 3-month recovery (both P<0.05). RCS analysis showed a linear dose-response relationship (P overall<0.001; P nonlinearity=0.540). MUL demonstrated moderate discriminative ability for 1-month (AUC = 0.822) and 3-month (AUC = 0.773) continence recovery. Conclusion Longer preoperative MUL was independently associated with higher likelihood of complete urinary continence recovery at 1 and 3 months after catheter removal, with an approximately linear dose-response relationship. MUL has good measurement reproducibility and moderate predictive value, supporting its potential as an imaging biomarker for preoperative continence risk stratification in RARP patients.