The findings of this study using cumulative sum analysis denote that a laparoscopic surgeon required 20 cases to master the procedure of intracorporeal overlap anastomosis. The CUSUM score of IAT increased up to the 20th case in Phase 1 (initial learning). The surgical technique was immature in Phase 1, peaked at the 21st case, and the score gradually decreased during Phase 2 (mastery), and a mature state was reached [7]. According to other reports, the number of cases necessary for the learning curve of laparoscopic colectomy was 15–35 cases [15, 16, 17]. These studies stated the learning curves for the overall surgical procedure. Meanwhile, our study was unique in that it focused on intracorporeal anastomosis, which is a process that requires advanced laparoscopic skills and is prone to the smallest differences in technical skill. During our analysis, the CUSUM score of ST was divided between Phase 1 (initial learning), Phase 2 (consolidation), and Phase 3 (mastery). When guiding and inserting the stapler into the small entry hole that was created in the bowel under the motion restriction by the laparoscopic port, there is a need for coordination between the surgeon who controls the stapler and the assistant who holds the bowel. In this process, the learning curve comprises of multiple factors related to the surgeon and assistant; therefore, it is thought that the CUSUM score of ST plateaued (consolidation phase) before transitioning into the downward trend of Phase 3 (mastery). Reducing the learning curve of this process requires shortening of Phase 2 by increasing training for coordination between the surgeon and assistant through simulations such as wet lab training. Meanwhile, the CUSUM score of LST depends on the skill of a single surgeon and was separated into 2 phases, with a peak reached at 22 cases. In general, there are three surgical sewing techniques: hand sewing, laparoscopic sewing, and robotic sewing. Hand sewing, which is the oldest, is the basis of open surgery and familiar to most surgeons. Robotic sewing, which uses advanced technology, is useful for intracorporeal anastomosis due to joint function [18]. Although there is no doubt that robotic surgery will become widespread among minimally invasive surgeries, it will still take some time to be accepted and available worldwide due to its high cost [19], and laparoscopic surgery will account for a large proportion of minimally invasive surgeries until then. Laparoscopic sewing is difficult because it is needle controlled and sutured with straight forceps without a joint function, and it takes time to master this technique. Therefore, it is of great significance to analyze the learning curve of the laparoscopic sewing. The number of cases required to shift to a downward trend in the CUSUM score of LST is lower than that of ST. In other words, it may be suggested that improving the skill of laparoscopic sewing may lead to a shortened learning curve of intracorporeal anastomosis in laparoscopic colectomy.
We have previously reported that the incidence of organ/space SSI was high in a study where saline that underwent lavage during surgery around the anastomosis was sampled after intracorporeal anastomosis and an examination of bacterial culture was conducted [20]. In this study, the incidence of organ/space SSI was significantly lower in Phase 2 than in Phase 1 of IAT for postoperative complications. This is thought to be due to the shortened Phase 2 in IAT, which reduced the intestinal release time and exposure time of the intestinal bacteria to the intracorporeal space. Furthermore, intracorporeal anastomosis has been reported to increase post-operative inflammatory responses such as white blood cells and C-reactive protein [20, 21]. Prolonged post-operative inflammation increases the duration of antibiotic use, time taken for first diet intake, and recovery of intestinal function. In this study, all four cases with organ/space SSI were drained by computed tomography-guided aspiration. For these reasons, it is thought that the postoperative hospital stay was significantly extended in Phase 1 relative to that in Phase 2. It was suggested that shortening of the learning curve of intracorporeal anastomosis may reduce the time for intestinal release into the abdominal cavity. This may lead to reduced postoperative complications and promote postoperative recovery.
The learning curve of a surgical procedure is thought to be governed by organizational factors (facilities, equipment), surgical team-related factors (experience, cooperation), case complexity, and surgeon-related factors (previous experience, natural abilities, motivation) [22]. Additionally, the operation time is affected by the surgeon’s competency, disease severity, and patient characteristics. Therefore, conventional chronological analysis or logistic regression analysis for operation time is not suitable for learning curve analysis, unless only cases with the same disease and patient factors are included. Furthermore, these analyses, even with selective inclusion of perfectly homogeneous groups, cannot reflect the actual clinical situation [23]. Meanwhile, the CUSUM method is suitable for observing the slow learning curve process from quantitative skills to qualitative changes, and it is more practical and accurate due to the small sample size and lack of need for grouping [24, 25]. The CUSUM analysis applied in this study is a good statistical method for determining the likelihood of changes and adverse events [22]. However, CUSUM analysis is not well suited for comparing differences between surgeons, and therefore, only one surgeon was included in this study. When introducing a new surgical procedure, it is important to understand the number of cases required to achieve skill proficiency and safety from the perspective of both efficient surgical education and patient safety management. Anastomotic leakage, which is the most critical complication in this study, was not observed in Phase 1 (initial learning) or Phase 2 (mastery). It was suggested that a surgeon who is a “qualified surgeon”, according to the Endoscopic Surgical Skill Qualification System, can safely perform intracorporeal anastomosis and achieves expertise after working on 20 cases. To the best of our knowledge, there have been no reports of research on learning curves that are specific to intracorporeal anastomosis in laparoscopic colectomy, and it is thought that these results will serve as a reference when facilities that have been conducting extracorporeal anastomosis introduce intracorporeal anastomosis in the future.
This retrospective observational study has several limitations. The number of cases was small (51 cases), only one surgeon with extensive experience in laparoscopic procedures participated, and only the CUSUM method was used to evaluate the learning curve, with multiple other methods not adopted. In the future, a multicenter clinical trial that involves multiple surgeons with difference levels of surgical experience and uses multiple evaluation criteria is necessary in order to evaluate the learning curve of intracorporeal anastomosis.
In conclusion, in our study, 20 cases were required for a laparoscopic surgeon to achieve expertise when conducting intracorporeal anastomosis in laparoscopic colectomy for colon cancer. Compared to the initial learning phase, the master phase had a significantly faster IAT, significantly decreased incidence of organ/space SSI, and significantly decreased postoperative hospital stay.