Patient Selection and the Apparent Laparoscopic Advantage in Rectal and Rectosigmoid Adenocarcinoma: A Single-Centre Propensity-Weighted Analysis of Confounding by Indication

Background and Objectives: Observational comparisons of laparoscopic and open colorectal resection are vulnerable to confounding by indication because fitter patients with earlier disease are preferentially offered the minimally invasive approach. Using a single-centre cohort as a worked example, we quantified how far the apparent laparoscopic advantage changed under progressively stricter control for measured confounding. Materials and Methods: In total, 89 adults undergoing elective resection for rectal or rectosigmoid adenocarcinoma were analysed by initiated approach (laparoscopic strategy, n = 61, of whom 19 were converted; planned open, n = 28) and, as a sensitivity analysis, by approach completed (laparoscopic, n = 42; open, n = 47). The primary outcome was major morbidity (Clavien–Dindo ≥ IIIa within 30 days); secondary outcomes were a 90-day textbook outcome and all-cause mortality, analysed with Kaplan–Meier and Cox methods (median follow-up 6 months, interquartile range 2–9). Approach effects were estimated as crude, Firth-penalised covariate-adjusted, stabilised inverse-probability-weighted, overlap-weighted, and doubly robust odds ratios, with balance quantified by standardised mean differences and sensitivity to unmeasured confounding by E-values. Results: Patients who completed laparoscopy were younger, less comorbid, and less often node-positive; baseline characteristics predicted the completed approach with a c-statistic of 0.83 (optimism-corrected 0.77). No patient died within 90 days. By initiated approach, major morbidity was 24.6% vs. 39.3% (crude odds ratio 0.50, 95% confidence interval 0.19–1.31; overlap-weighted 0.90, 0.30–2.70), and the 90-day textbook outcome was 41.0% vs. 42.9% (0.93, 0.37–2.29). By completed approach, the crude odds ratio for major morbidity was 0.17 (0.06–0.50), the Firth-adjusted 0.36 (0.11–1.14), and the overlap-weighted 0.96 (0.33–2.80); the crude mortality hazard ratio of 0.24 (0.07–0.83) became 1.06 (0.30–3.78) after weighting, with one influential patient. Inverse probability weighting left seven of nine covariates above a standardised difference of 0.10; overlap weighting balanced means by construction at the cost of a smaller target population. Conclusions: In this small cohort, the associations between approach and outcome changed substantially after adjustment and weighting, but the adjusted estimates remained imprecise and vulnerable to residual and unmeasured confounding, so neither a benefit nor its absence can be inferred. Observational comparisons of surgical approach should define exposure by initiated approach, report the balance actually achieved, and present sensitivity analyses before any superiority claim.