Laparoscopic surgery has become the standard of care in colorectal surgery. However, laparoscopic surgery can be challenging when operating with straight and rigid instruments in the confines of the narrow pelvis. Furthermore, there is still concern about the safety of laparoscopic rectal surgery compared with open surgery. These concerns increased following the AlaCart and the ACOSOG Z6051 trials both of which failed to show non-inferiority of laparoscopic surgery to open surgery for pathological outcomes [14, 15].

The development of robotic assisted laparoscopic surgery with superior views, improved instrument articulation and enhanced dexterity has emerged as a potential solution to the limitations of conventional laparoscopic surgery. Despite this, the role of the robotic system in colorectal surgery is still debated, and its utility in obese and morbidly obese patients has been less than clear. To date, there has been sparse literature on whether the technical challenges associated with obesity may be improved by the technical advantages offered by robotic surgery, or whether obesity may hinder the robotic platform due to the difficulties of port placement, docking and arm collisions.

In this study, we compared 561 patients who had robotic assisted rectal resection with 1824 patients who had conventional laparoscopy using data from the ACS-NSQIP database. The unplanned conversion to open following laparoscopic surgery for obese patients was very high (24%). In comparison, the rate of conversion to open in previous studies that included experienced laparoscopic surgeons was much lower (9–12%) [7, 14, 15]. One explanation to this is that obesity represents a significant challenge to laparoscopic rectal surgery, especially within the confines of a narrow pelvis in a morbidly or ‘extremely’ obese patient. Another explanation is that the results of this data come from surgeons with varying experience in laparoscopic surgery.

Overall, robotic surgery significantly reduced the rate of unplanned conversion to open compared to conventional laparoscopy (14 vs 24%, P < 0.0001) but was associated with longer operative time (248 min vs 215 min, P < 0.0001). There was no significant difference in systemic sepsis, surgical site infection or length of hospital stay. When looking at the subset of morbidly obese patients (BMI 35 or greater), the reduction in the rate of conversion to open was also significantly lower in the robotic group. This demonstrates that the benefits of robotic technology with its articulating wrists, 3D vision and surgeon-controlled robotic arms can still counter the challenges associated with not only obese but also morbidly obese patients. A sub-analysis for ‘extreme’ obesity was not performed due to small numbers in this group.

Multivariate logistic regression analysis of variables predicting unplanned conversion to open showed that robotic-assisted surgery was associated with fewer unplanned conversions to open with adjusted odds ratio 0.28. Other predictors of increased rate of unplanned conversion to open included male gender, ASA 3 or more, preoperative weight loss, prolonged operative time, stoma formation and hypertension. Previous studies have identified male sex, advanced tumour stage, and hypertension as additional risk factors for unplanned conversion to open in both laparoscopic and robotic colorectal surgery [16,17,18]. Preoperative weight loss and the formation of stoma could be indicators for more advanced disease, and this could explain their association with increased risk of conversion to open. The evidence to support ASA as a predictor of conversion to open is conflicting. While some studies identified ASA of 3 or more as a predictor of unplanned conversion to open, other studies failed to confirm this [16, 19].

Robotic assisted rectal resection has been compared to laparoscopy in four retrospective studies using data from the ASC-NSQIP [20,21,22,23]. All studies showed reduction in the rate of unplanned conversion to open associated with robotic surgery and three of them reported reduced length of hospital stay with robotic surgery [20,21,22]. The rate of post-operative complications including anastomotic leak and surgical site infections was the same following both laparoscopic and robotic rectal resections. Ahmed et al. [24] prospectively compared laparoscopic and robotic rectal resection in high-risk patients. High risk factors included male gender, obesity (BMI > 30), preoperative chemoradiation, tumour lower than 8 cm from the anal verge and previous abdominal surgery. In 184 high-risk patients (99 robotic surgery and 85 laparoscopic surgery), robotic surgery was associated with fewer conversions to open (0 vs 5%, P = 0.043), shorter hospital stay (7 vs 9 days, P = 0.001) and higher sphincter preservation rate (86 vs 74%, P = 0.045).

Two studies compared robotic and laparoscopic rectal resections in obese patients (BMI > 30) [12, 13]. Panteleimonitis et al. [12] retrospectively matched 63 patients with robotic rectal resection with 61 patients who had laparoscopic surgery. As expected, operative time was longer in the robotic group compared to conventional laparoscopy (260 min vs 215 min, P = 0.0001). However, length of hospital stay was shorter in the robotic group (6 vs 8 days, P = 0.014) and 30-day readmission rate was lower (6.3 vs 19.7%, P = 0.033). On the other hand, there was no difference in the rate of post-operative complications, anastomotic leak, lymph node yield or Ro clearance between the two groups. Although conversion to open surgery was fewer with robotic surgery, this did not reach statistical significance (0 vs 3.3%, P = 0.24). Gorgun et al. [13] retrospectively compared 29 patients who had robotic rectal surgery with 27 patients who had laparoscopic surgery. Like the previous study, there were fewer conversions to open with robotic surgery, but this did not reach statistical significance (3.4 vs 18.5%, P = 0.09). We may assume that this result was underpowered due to small sample size. Return of bowel function was faster following robotic surgery (3 days vs 4 days, P = 0.01), and hospital stay was shorter (6 days vs 7 days, P = 0.02). There was no difference in the rate of postoperative complications including anastomotic leak and surgical site infection between robotic and laparoscopic surgery. There was also no difference between completeness of mesorectal fascia excision or lymph node yield between the two groups.

Shiomi et al. compared short-term outcomes of robotic versus laparoscopic rectal cancer resection in obese patients defined by visceral fat area of ≥ 130 cm2, assessed by computer tomography (CT) [25]. They compared 52 patients who had robotic rectal surgery with 30 patients who underwent conventional laparoscopy. There were no conversions to open in both groups. Overall complication rate was significantly lower in the robotic group (9.6 vs. 30%, P = 0.04) and there was shorter hospital stay following robotic surgery compared to laparoscopy (7 days vs 9 days, P = 0.001).

Our study has several limitations. The study is a retrospective analysis of a prospectively maintained database which makes it prone to inclusion bias. In this study, more patients in the robotic group had mechanical bowel preparation, received preoperative oral antibiotics and had a formation of stoma. Although these do not directly impact on the rate of conversion to open, these peri-operative interventions may influence many of the post-operative outcomes including anastomotic leak, systemic sepsis and surgical site infection. There were also differences in patient demographics, lack of standardization of surgical technique and definition of conversion to open, inclusion of outcomes from low volume centers as well as surgeons with different levels of expertise in both laparoscopic and robotic colorectal surgery.