Currently, the main therapy for rectal cancer is laparoscopic resection. Rectal cancer is located in a narrow and rigid space of the pelvic cavity that has many important vessels and nerves. This situation poses a great technical challenge to surgeons. Furthermore, TME as a standard operation for rectal cancer, requires complicated laparoscopic manipulations to reach the extremes of the pelvis for the complete resection of the rectum and peripheral lymph nodes . The above situation with the addition of using a straight and rigid laparoscopic instrument makes laparoscopic TME surgery a highly difficult technique. The Micro Hand S robot system, the first domestically produced Chinese minimally invasive surgical robot system, possess the following features: an 3D vision imaging system contributing to a more accurate spatial orientation, motion scaling allowing for a more precise manipulation, and a wristed instrument increasing the dexterity of the instrument. All of these characteristics facilitate TME surgery in a small space. Therefore, based on the above consideration, we selected rectal cancer surgery to evaluate the safety and feasibility of the Micro Hand S robot in it’s initial phase. In the current study, we found that the R-TME group was with a less blood loss, shorter time to first flatus and first liquid intake than the L-TME group, without compromising on other outcomes.
The patient characteristics of the two groups were comparable. Notably, the number of patients who received neoadjuvant CRT was small because selective neoadjuvant CRT was administered in this study. In fact, for tumors and lymph nodes located in the TME plane without suspicious or positive CRM, standard TME surgery can promise a curative resection, and neoadjuvant CRT is not indispensable . Moreover, neoadjuvant CRT may induce tissue edema, which increases the difficulty of pelvic dissection and the risk for intra- and postoperative complications . Therefore, selective neoadjuvant CRT was reasonable in this study. In addition, neoadjuvant CRT decreases the number of positive lymph nodes , so the number of positive lymph nodes in this study (median: 2.5 in the R-TME group and 2.0 in the L-TME group) was higher than that in other series [7, 13].
The R-TME group had less intraoperative blood loss (95.2 vs. 130.0 ml) than the L-TME group (p < 0.05). To our experience, with a high resolution view, the surgeon can easily identify the potential space of anatomy with few vessels and the dissection can be performed more smoothly. The wristed instruments unlike the rigid laparoscopic instruments demonstrated flexible performance during robotic surgery. What’s more, the Micro Hand S was equipped with motion scaling strategies  and the surgeons can downscale the motion of instruments at the ratio of 1:3, 1:6, 1:10 as needed. In the narrow pelvic cavity, the surgeon adopted a ratio of 1:3 to realize a precise dissection. All these features improved accuracy of the manipulations which were helpful to reduce blood loss. Meanwhile, these technical advantages helped to reduce bowel injury and promised a quicker recovery of the bowel.
In this study, the mean operative time was not significantly different between the R-TME and L-TME groups (288.3, 265.0 min), although the operative time of the R-TME group was 23.3 min longer than that of the L-TME group. However, several studies have shown that the da Vinci surgical robot-assisted TME had a significant longer operative time than L-TME for rectal cancer [15–17]. The reasons below may contribute to this fact: (i) The patients characteristics may be responsible for this fact, such as the higher tumor location in the robotic group. The distance from anal verge reflected the depth of dissection in the pelvis and surgical difficulty . Therefore, the relative high location of lesions may decrease surgical difficulty, thus reducing the operative time; (ii) In this study the surgeon had rich experience using the da Vinci surgical robotic system for rectectomy. Meanwhile, the Micro Hand S and da Vinci robot operated in a similar manner. This situation dramatically facilitated the learning curve of the Micro Hand S robot for rectal resection. The surgeon overcame the learning curve and exhibited a stable operation performance after a few cases; (iii) The adopted trocar position, as seen in Fig. 2, permitted completion of the surgery after the initial docking of the robot and avoided a re-docking, further reducing the operative time. Encouragingly, our data was similar to the result of the ROLLAR trial for robotic surgery (288.3 vs. 298.5 min) . A low conversion rate is an important advantage of robotic surgery for rectal cancer, and the reported conversion rate ranged from 1.31–5.68% [20–22]. In our study, one patient was converted because of an ureteral injury due to adhesion, and the conversion rate (4.76%) was acceptable.
The comprehensive complication index (CCI) that integrated all postoperative complications has shown to be an effective measure to evaluate the differences in treatment effects . The current study demonstrated that both groups had similar CCI. The rate of severe complications (≥ grade III) in the R-TME group was 4.8%, similar to the findings of Park et al. (9.8%)  and Shiomi et al. (2.7%) , although the overall morbidity (42.8%) was higher than their results (29.3%,19.4%). In the previous studies the most common complication was anastomotic leakage, but it did not occur in our study. The low anastomotic leakage rate was related in part to the low rate of neoadjuvant CRT and the inclusion of major upper-middle cases.
The quality of the TME specimen and the circumferential surgical margin (CRM) associated with recurrence rate are important prognostic factors for rectectomy [26, 27]. In the current study, 19 patients (90.6%) were classified as the grading of “complete” in the R-TME group. Similarly, in the literature, Kim et al.  reported 32 “complete” patients (97.0%) and Aselmann et al.  reported 43 “complete” patients (97.7%). However, the high-quality evidence from the ROLLAR trail showed that 178 patients (75.4%) were classified as “complete” , significantly lower than our result. The differences might be influenced by the higher tumor location in our study. A clear CRM with a distance of > 1 mm is the most acceptable standard . In our study, two patients in the R-TME group had positive CRMs (< 1 mm) because of the low tumor location and there were no local recurrence during the follow-up. The pathological outcomes indicated that the Micro Hand S robot-assisted TME can be successfully performed. With the aid of the 3D view, the robotic system provided the possibility of visualizing the membrane anatomy and dissected along the space between the two layers of the pelvic fascia around the rectum, which was particularly beneficial to achieve curative resection.
Functional outcomes were assessed in three aspects: sphincter, bladder and sexual functions. Because of inadequate data about female patients, the analysis only included male patients. The scores worsened after operation and progressively improved at 3/6 months post-operation, with no significantly difference between the two groups. As shown by Luca et al. , although the features of surgical robot were helpful in identification and preservation of pelvic autonomic nerves, no evidence shown a superiority in performing nerve-sparing rectal cancer surgery. The scores at 6 months post-operation did not reach the level of pre-operation and need to take longer time to observe the change in the future study.
The limitations of this study were as follows. First, the study was with a small sample size and a study with large sample size is essential to gain a better understanding of robotic surgery. Second, we included the robotic cases in the learning phase, which may bias our results. Third, the Micro Hand S robot as the first generation, is still in the clinical stage. Therefore, we did not include complicated cases in this study, such as ultra-low rectal cancers. This selection bias inevitably impaired the objectivity of the results. By performing complicated cases in the future, the advantages of robotic surgery will be fully demonstrated. In addition, the long-term oncologic outcomes were not included in this study and should be evaluated in future studies.