Prior experience in laparoscopic rectal surgery can minimise the learning curve for robotic rectal resections: a cumulative sum analysis

The learning curve for robotic colorectal surgery is ill-defined. This study aimed to investigate the learning curve of experienced laparoscopic rectal surgeons when starting with robotic total mesorectal excision (TME) using cumulative sum (CUSUM) charts. This retrospective case series analysed patients who underwent curative and elective laparoscopic or robotic TMEs for rectal cancer performed by two surgeons. The first consecutive robotic TME cases of each surgeon were 1:1 propensity score matched to their laparoscopic TME cases using age, body mass index, American Society of Anesthesiologists grade, T stage (AJCC) and tumour location height. The matched laparoscopic cases defined individual standards for the quality indicators: operating time, R stage, lymph node harvest, length of hospital stay and major complications (Clavien-Dindo grade 3-5). Deviation of more than a quarter of a standard deviation from the mean for the continuous indicators, or exceeding the observed risk for the binary indicators was defined as off-target with an upward inflection in the CUSUM curve. From 2006 to 2015, 384 (294 laparoscopic; 90 robotic) TMEs met the inclusion criteria. Surgeon A performed 206 (70.1%) of the laparoscopic and 43 (47.8%) of the robotic cases. Surgeon B performed 88 (29.9%) of the laparoscopic and 47 (52.2%) of the robotic cases. After matching, no covariate exhibited an absolute standardised mean difference > 0.25. For surgeon A, the CUSUM curves showed no apparent learning process compared to his laparoscopic standards. For surgeon B, a learning process for operation time, lymph node harvest and major complications was demonstrated by an initial upward inflection of the CUSUM curves; after 15 cases, all quality indicators were generally on target. For experienced laparoscopic colorectal surgeons, the formal learning process for robotic TME may be short to reach a similar performance level as obtained in conventional laparoscopy.