Learning curves for minimally-invasive intersphincteric resection using risk-adjusted cumulative sum curves

Background: Achieving competency is crucial to ensure optimal outcomes in minimally invasive Intersphincteric resection. This study documents the learning curves for minimally invasive Intersphincteric resection using risk-adjusted cumulative sum curves with the surgical failure as a composite endpoint, providing a dynamic assessment of performance and competency attainment. Methods: All consecutive minimally invasive Intersphincteric resections performed by a single team of surgeons at a tertiary referral colorectal cancer unit were audited. Surgical failure was defined as any of the following: positive resection margin, local recurrence, or unreversed ostomy at one year. Risk-adjusted cumulative sum and Bernoulli cumulative sum curves were used for sequential assessment of performance. Results: Amongst 310 Intersphincteric resections, surgical failure was observed in 66 patients (21%). A positive margin was seen in 11 patients (3.5%), unreversed stoma at one year in 53 (17%), and local recurrence in 18 patients (5.8%). The risk-adjusted cumulative sum identified the first inflexion point corresponding to the achievement of competency after the 40th case. Further, other instances of higher-than-predicted surgical failures were observed and explained. While laparoscopic Intersphincteric resection risk-adjusted cumulative sum curves mirrored the curves for entire cohort, the robotic curves could not identify any discernable inflexion. Conclusions: The learning curve for Intersphincteric resection by minimally invasive technique was achieved after the 40th case for a team that was trained in minimally invasive colorectal surgery. The broader applicability of cumulative sum curves for early detection of deterioration in outcomes highlights the need for their wider use in procedural monitoring.