Association of narrow pelvis and body composition with anastomotic stricture following total proctocolectomy with ileal pouch–anal anastomosis for ulcerative colitis

Abstract Background Anastomotic stricture (AS) is a significant complication following total proctocolectomy with ileal pouch–anal anastomosis (TPC–IPAA) for ulcerative colitis (UC) that impairs defecation and quality of life. However, the underlying mechanism remains unclear. This study aimed to investigate the association between body composition, narrow pelvis, and AS development. Methods This retrospective cohort study included 55 patients with UC who underwent TPC–IPAA between 2010 and 2023. Preoperative computed tomography was used to assess the skeletal muscle index (SMI), visceral fat index (VFI), and pelvic dimensions, including interspinous distance, true conjugate line and pelvic outlet line. To account for both anteroposterior and transverse pelvic dimensions, the product of the true conjugate line and interspinous distance was calculated as a composite measure of pelvic size and was defined as the pelvic index. Severe AS was defined as a stricture requiring endoscopic balloon dilatation within 1 year after surgery. Firth penalized logistic regression analysis was conducted to evaluate factors associated with severe AS. Results Severe AS occurred in 11 patients (20.0%) and was associated with a significantly lower pelvic index ( p = 0.022), higher SMI ( p = 0.029), and shorter interspinous distance ( p = 0.030). Receiver operating characteristic analysis using the Youden index was performed to determine cutoff values for the continuous variables. In the univariable Firth penalized logistic regression analysis, high BMI, SMI, and VFI, as well as short interspinous distance, short pelvic outlet line, short true conjugate line, and low pelvic index were significantly associated with severe AS. In the multivariable Firth penalized logistic regression analysis including SMI, VFI, and the pelvic index, a low pelvic index remained significantly associated with severe AS (OR, 6.76; 95% CI, 1.35–38.50; p = 0.019), whereas high SMI showed a tendency toward an association with severe AS but did not reach statistical significance (OR, 4.82; 95% CI, 1.00–25.59; p = 0.0504), and the association between high VFI and severe AS lost statistical significance. Conclusions A narrow pelvis, particularly a low pelvic index, may be associated with severe AS following TPC-IPAA for UC. Body composition characterized by high skeletal muscle mass and increased visceral fat may also be relevant, although these findings remain exploratory. These findings highlight the potential importance of preoperative evaluation of pelvic anatomy and body composition.