Obesity is a negative predictor of success after surgery for complex anal fistula

Background: It was the aim of this study to compare the outcome of surgery for complex anal fistulas in obese and non-obese patients. Methods: All patients with complex anorectal fistulas who underwent fistulectomy and/or rectal advancement flap repair were prospectively recorded. Surgery was performed in a standardized technique. Body mass index (BMI [kg/m(2)]) was used as objective measure to indicate morbid obesity. Patients with a BMI greater than 30 were defined as obese, and patients with a BMI below 30 were defined as non-obese. The parameters analyzed related to BMI included success or failure, and reoperation rate due to recurrent abscess. Success was defined as closure of both internal and external openings, absence of drainage without further intervention, and absence of abscess formation. Results: Within two years, 220 patients underwent advancement flap repair and met the inclusion criteria. 55% of patients were females, mean age was 39 (range 18-76) years, and the majority of fistulas were located at the posterior site. 69% of patients (152/220) were non-obese (BMI < 30), whereas 31% (68/220) were obese (BMI > 30). After a median follow-up of 6 months, primary healing rate ("success") for the whole collective was 82% (180/220). Success was significantly different between non-obese and obese patients: In non-obese patients, recurrence rate was significantly lower than in obese patients (14% vs. 28%; p < 0.01). Moreover, reoperation rate due to recurrent abscess with the need for seton drainage in the failure groups was significantly higher in obese patients when compared to non-obese patients (73% vs. 52%; p < 0.01). Using multivariate analysis, obesity was identified as independent predictive factor of success or failure (p < 0.02). Conclusion: Obese patients are at higher risk for failure after surgery for complex anal fistula.