Sex-Stratified Analysis of Maximum Squeeze Pressure Interaction with Rectal Push Pressure and Rectoanal Inhibitory Reflex in External Rectal Prolapse Using High-Resolution Anorectal Manometry

Abstract Purpose External rectal prolapse (ERP) carries high risks of recurrence, incontinence, and constipation. Which three-dimensional high-resolution anorectal manometry (3D HR-ARM) phenotype identifies the most severe functional impairment remains undefined. We established a sex-stratified interaction model between maximum squeeze pressure (MSP) and rectal push pressure (RPP) or the rectoanal inhibitory reflex (RAIR). Methods In this retrospective case–control study, 167 patients with ERP (69 women, 98 men) and 142 healthy volunteers (HVs) underwent 3D HR-ARM, and defecography was performed in all ERP patients. Logistic regression and Rothman's additive interaction models quantified MSP–RPP (women) and MSP–RAIR (men) interactions, with bootstrap 95% confidence intervals (CIs). Results In women, the R 11 phenotype (concomitant MSP and RPP reduction) carried the highest odds of ERP (odds ratio [OR] 213.50, 95% CI 52.50–773.56), with a super-additive effect ( S = 6.14). In men, reduced MSP with preserved RAIR ( R 10 ) carried the highest odds (OR 21.50, 95% CI 6.43–119.07), and the MSP–RAIR interaction was antagonistic ( S = 0.31; multiplicative interaction OR 0.12, P = 0.025). R 11 specificity was 98.6% in women and 88.6% in men. Combined MSP + RPP and MSP + RAIR models yielded areas under the curve of 0.938 and 0.731. Conclusions Sex-specific interaction phenotyping of 3D HR-ARM reveals divergent pathophysiological patterns in ERP—synergistic MSP–RPP failure in women and MSP-dominant dysfunction with antagonistic RAIR modulation in men—and, integrated with defecography-based anatomical classification, may inform risk stratification and individualized surgical planning.