Effect of Collagen Adjunct After Fistulotomy and Endorectal Advancement Flap on Healing and Recurrence in Primary Cryptoglandular Anal Fistula: A Retrospective Comparative Study

Background Collagen scaffolds are increasingly used as adjuncts in sphincter-preserving surgery for anal fistula, yet comparative data when combined with endorectal advancement flap are limited. Methods Single-center retrospective cohort of 100 consecutive adults with primary cryptoglandular fistula (January 2023–December 2024). Patients underwent fistulotomy plus endorectal advancement flap with (Collagen, n = 50) or without collagen (Control, n = 50). The prespecified primary endpoint was fistula/surgical site discharge at 2 months. Secondary endpoints were fistula/surgical site discharge at 6 and 12 months, reoperation by 12 months, pain, pruritus, erythema, incontinence, stenosis, and wound dehiscence. Analyses used chi-square/Fisher’s exact tests and multivariable logistic regression adjusting for age, sex, smoking, fistula class, and diabetes. Effect sizes are reported as risk ratio (RR) and absolute risk difference (ARD) with 95% CIs. Results Baseline characteristics did not differ between the groups. Discharge at 2-monts was significantly less likely in the group treated with collagen (32% vs 56%; RR 0.57, 95% CI 0.36–0.90; ARD − 24%, 95% CI − 42% to − 6%; p  = 0.027). In adjusted analysis, collagen adjunct treatment remained associated with reduced discharge (aOR 0.40, 95% CI 0.17–0.95). At 12 months, discharge (14% vs 30%; RR 0.47, 95% CI 0.21–1.05) and reoperation (0% vs 0%) favored the collagen group descriptively, but did not reach conventional significance. No incontinence events occurred in the collagen group. Conclusions Collagen adjunct in patients undergoing fistulotomy plus advancement flap improved 2-month wound outcomes and showed favorable later trends (at 6 and 12 months) without compromising fecal continence. Prospective randomized trials are warranted.