Effects of Rectal Anastomotic Configuration and Circular Stapler Diameter on Postoperative Low Anterior Resection Syndrome: A Comparative Clinical Study

Background Low Anterior Resection Syndrome (LARS) is a major determinant of long-term anorectal dysfunction after sphincter-preserving rectal cancer surgery. The mechanical properties of the anastomosis—including its configuration and circular stapler diameter—may influence neorectal compliance, sensory function, and postoperative evacuation dynamics. This study aimed to define the independent contributions of anastomotic configuration and stapler diameter to LARS development. Methods A retrospective cohort of 446 patients who underwent total mesorectal excision (TME) and low anterior resection between 2015 and 2023 was reviewed. A total of 309 patients who had at least 18 months of functional follow-up and validated LARS assessment were included. All anastomoses were created using double-row circular staplers, in either end-to-end or side-to-end configuration. Stapler diameter (28–29 mm vs 31–33 mm), anastomotic level, neoadjuvant treatment protocol, tumour morphology, and total dissected lymph node count were recorded systematically. Functional outcomes were assessed with the validated LARS score. Independent predictors of LARS were identified using backward stepwise multivariable logistic regression. Results The overall LARS incidence was 28.5%. In the end-to-end subgroup, age (OR 1.096) and metastatic lymph node count (OR 1.221) were independent predictors of LARS. In the side-to-end subgroup, a larger stapler diameter (31–33 mm) markedly increased LARS risk (OR 6.910), while age remained an independent determinant (OR 1.055). In the full cohort, advanced age (OR 1.063), long-course neoadjuvant radiotherapy (OR 2.248), and larger stapler diameter (OR 2.395) were independently associated with LARS. Conclusion Anastomotic configuration was not independently associated with postoperative LARS development, whereas larger stapler diameter was significantly and independently associated with an increased risk of LARS, particularly in side-to-end anastomoses. Advanced age and long-course neoadjuvant radiotherapy were also consistently associated with impaired long-term functional recovery. These findings underscore the importance of meticulous intraoperative stapler selection and individualised surgical planning, as technical decisions may have measurable long-term effects on anorectal function.