In this study, we conducted 65 cases of full dissection of LPLNs with TME of rectal cancer using the Da-Vinci Si and Xi platforms and found favorable safe and feasible outcomes. The robotic platform has potential benefits, allowing for a fine dissection through magnification and three-dimensional views and articulated arm movement in a narrow operation space [6, 7, 14–16]. This has consequently increased the number of robot-assisted rectal cancer surgery worldwide [17]. We believe that with the increasing adaptation of robotic surgery and the accumulation of surgical techniques, the number of patients undergoing surgery for advanced low rectal cancer with LPLN metastasis will be increasing.
Our data were comparable to the literature in three main aspects. The first aspect is the procedure time. Procedure time may have a potential effect on short-come complications [18]. Our mean operation procedure time of 306.8 min is comparable to the mean of 476 min (320–683) min reported by Kagawa et al. [9], a median of 420 (313–530) min reported by Peacock et al. [11], and a mean of 260 min reported by Choi et al. [5]. The unilateral LPND time was 38.6 min, which is comparable with 41.0 min in the report by Choi et al. This study also reported laparoscopic LPND time of 35 min.
The second aspect is the number of retrieved LPLNs. Better oncologic results strongly correlated with the number of retrieved LPLNs [12]. Our study reported an average of 6.8 (1–24) lymph nodes, and 15 (23.0%) patients were positive for metastasis, which is comparable to results from studies of patients undergoing open and laparoscopic surgery [5, 11, 19, 20]. In other reports, the median number of retrieved LPLNs ranged from 4 to 10, and the positivity of the lymph nodes ranged from 10.5–37%, which was comparable to our results.
The final aspect refers to the postoperative morbidity within 90 days. Our value of 15.4% was comparable to 10–22.9% in other reports [5, 9, 11] although the definition of complication in these reports included those arousing from mesorectal excision. In this study, we focused on the complications directly related to LPND, such as urogenital dysfunction, lymphocele, pelvic abscess, and neuropathies, found within 90 days after the operation. Lymphocele was the most common postoperative morbidity, followed by pelvic abscesses. However, the occurrence rate of lymphocele is quite difficult to compare with those in other studies because only a few studies have focused on lymphocele in low rectal cancer [21]. Considering that the occurrence rate of infected lymphocele after lymphadenectomy for gynecologic malignancy was 4.4% [22], the occurrence rate of lymphocele and pelvic abscess in this study is thought to be comparable.
One technical tip that we utilized to shorten the operation time and assure clear and safe dissection of LPLNs was the shift of docking ports when performing right-sided LPND. Several docking methods of robotic LPND are reported in the literature, that is, some methods were similar to laparoscopic approaches [14], and other methods were based on placements of the robot arm [9]. In the case of the docking method of our institute for right-sided LPND, the camera arm is shifted to the third port to have two left arms. This may provide a mirror-like image to the left-sided LPND and would help show familiar planes to the operator. Another possible advantage of this shifting technique is overcoming the limited range of robot arm motion by switching the direction of the camera. Although further studies are needed to fully evaluate the potential advantages of this technique, we are confident that this achieved a convenient working space.
This study has some limitations. First, selection bias may exist as this study was held retrospectively. To mitigate this, we included all consecutive patients undergoing robotic LPND during the study period. Second, our data was not validated from laparoscopic or open LPND. Although our center also performs open and laparoscopic LPND, a systemic registry is lacking, and there is heterogeneity in the treatment and results. Thus, the only way to validate our study was to compare it with the literature. Finally, complications such as urogenital dysfunction may be underreported because the outcomes were not actively surveyed and were collected from electronic medical record data.