Supplementary Material for: Effect of First Assistant on Anastomotic Leakage after Rectal Cancer Surgery with Double-Stapling Anastomosis: A Propensity Score Matching Analysis

Background: Proper handling and firing of the circular stapler are important for secure anastomosis in rectal cancer surgery. This study aimed to investigate the association between the first assistant and anastomotic leakage (AL) after rectal cancer surgery with double-stapling anastomosis. Methods: Patients with primary rectal cancer who underwent low anterior resection with double-stapling anastomosis between January 2015 and September 2019 were included. Data on clinicopathological characteristics, including the first assistant’s sex and experience level, were retrospectively reviewed, and the risk factors for AL were analyzed using propensity score matching analysis. Results: Among 758 rectal cancer surgeries, residents participated in 401 (52.9%) surgeries and fellows participated in 357 (47.1%) surgeries as first assistants. After propensity score matching (n = 650), AL occurred in 5.4% (35/650). The first assistant’s experience level (resident: 5.5% vs. fellow: 5.2%, p = 0.862) and sex (male: 5.4% vs. female: 4.9%, p = 0.849) were not associated with the occurrence of AL. Male sex in patients was the only significant predictive factor for AL (odds ratio = 2.804, 95% confidence interval 1.070–7.351, p = 0.036). Conclusion: The first assistant’s sex and experience level were not associated with AL after rectal cancer surgery with double-stapling anastomosis. These findings may justify resident participation in rectal cancer surgeries in which circular staplers are used.