Learning curves for minimally invasive total mesorectal excision beyond the competency phase - a risk-adjusted cumulative sum analysis of 1000 rectal resections.

Abstract

The learning curve of total mesorectal excision (TME) by minimally invasive surgery (MIS) beyond the competency phase has not been adequately reported with large numbers or using a statistical control limit. The aim of this work was to study the learning curve of MIS TME in the proficiency phase. Risk-adjusted (RA) cumulative sum (CUSUM) and RA Bernoulli CUSUM charts were plotted for sequential MIS TME performed by a surgical team over 1000 cases. Surgical failure, a composite endpoint of conversions, complications of grade IIIA or above, R1 resections and inadequate nodal yield were used to monitor the performance. The RA CUSUM detected an inflection point around the 600th operation. Two peaks were identified that could be traced back to probable causes of surgical failure. Similar inflection points were detected at the 450th case for laparoscopic TME and the 367th case for sphincter preservation. No single definite threshold point was noticed for robotic or abdominoperineal operations. At no point did the curves cross the safety threshold. The probability of surgical failure reduced with increasing experience in the multivariate regression (OR 0.899, p = 0.000). This association persisted irrespective of the surgical approach (laparoscopic versus robotic) or the type of operation (sphincter preservation versus abdominoperineal resection). The learning curves for MIS TME did not cross the safety threshold beyond the competency phase. However, a 10% reduction of relative risk in surgical failure was observed for every 100 cases operated on.