Clinical Review State of the Art Review

# The role of robotics in colorectal surgery

BMJ 2018; 360 (Published 12 February 2018) Cite this as: BMJ 2018;360:j5304
1. Christina L Cheng, fellow in colorectal surgery1,
2. Craig Rezac, lead physician colorectal surgery2
1. 1Colon and Rectal Clinic, Swedish Medical Center, 1101 Madison Avenue, Ste 510, Seattle, WA 98104, USA
2. 2Virginia Hospital Center Physician Group, 1625 N George Mason Drive, Ste 334, Arlington, VA 22205, USA
1. Correspondence to: C L Cheng christinal.cheng{at}gmail.com

## Abstract

Studies of laparoscopic approaches in colorectal surgery support the use of such methods. Compared with the open approach, laparoscopy reduces rates of postoperative complications and decreases length of stay, while providing equivalent oncologic outcomes. Nevertheless, much of colorectal surgery is still being performed by the open approach. This may be partly due to the technical challenges in performing laparoscopy, particularly when working in narrow spaces such as the pelvis. Moreover, some of the current literature has questioned the oncologic outcomes after laparoscopic surgery for rectal cancer. Robotic surgery has been heralded as the minimally invasive tool that can overcome these challenges. It has the advantages that it provides a three dimensional image, uses wristed instruments, and has a computer interface that allows for fluid and accurate movements. Overall, current evidence suggests that robotics is safe and feasible in colorectal surgery, and that short term and long term outcomes are comparable to those seen for laparoscopic approaches. Studies on the costs of robotic surgery show conflicting results, and this is arguably one of the biggest disadvantages of its use. Because robotic surgery is a relatively new technology, few large high quality studies are available. Most of the published studies in this area consist of retrospective reviews, case matched studies, and national database reviews. Large randomized prospective studies are needed to further support its use.

## Introduction

The use of minimally invasive surgery has increased dramatically over the past four decades and more recently robotic assisted surgery has led the advances in this field. Robotic surgery has been used in most surgical fields, including gynecology, urology, cardiothoracic surgery, general surgery, surgical oncology, bariatric surgery, and colorectal surgery. Many procedures such as hysterectomies, prostatectomies, hernia repairs, cholecystectomies, and colectomies have been performed with robotics.

Robotics in colorectal surgery has been gaining interest since the da Vinci surgical system (Intuitive Surgical) entered the market in 2001. The “surgical robot” emerged to overcome the disadvantages of laparoscopic surgery.

This review will assess the evidence on the feasibility, safety, efficacy, and costs of robotics in colorectal surgery and compare it with open and laparoscopic approaches.

## Sources and selection criteria

We used the PubMed database to search the terms “robotic,” “robotic versus laparoscopic,” and “colorectal surgery” from the year 2007 to April 2017. Other searched terms included “rectal cancer,” “right colectomy,” “low anterior resection,” “tatme,” “tamis,” “tme,” “intracorporeal anastomosis,” “obesity,” and “cost.” The reference sections of articles were also searched for relevant studies. Because robotic surgery is a relatively new technique, the number of large prospective multicenter randomized studies is limited. To present a thorough review of the current literature, we included a wide variety of studies, including single center retrospective reviews, large database studies, systematic reviews, meta-analyses, case matched studies, and prospectively randomized studies. We included studies from countries outside of the United States. Case reports and observational studies were excluded. We also included abstracts from the 2015 (Boston, Massachusetts) and 2016 (Los Angeles) annual meetings of the American Society of Colon and Rectal Surgeons (ASCRS).

## Use of laparoscopy in colorectal surgery

The use of laparoscopy began in the field of gynecology and it was first introduced into general surgery in the late 1980s1; the first laparoscopic appendectomy was performed in 19832 and the first laparoscopic cholecystectomy in 1987.3 This led to the use of laparoscopy in all surgical subspecialties,4 including colorectal surgery. The first laparoscopic-assisted sigmoidectomy was performed in 1990.5

As the surgeons’ technical skill in laparoscopic surgery rose, so did its acceptance. The advantages of laparoscopy became clear–smaller, more cosmetic incisions, a reduced risk of wound infections and venous thromboembolism, decreased pain and use of narcotics, shorter hospital stays, quicker return to work, and improved postoperative immune function.6789 Studies of laparoscopy in colorectal surgery showed evidence of the benefits of this approach.

Several randomized controlled trials (RCTs)—the Clinical Outcomes of Surgical Therapy (COST) study with about 400 patients in each group,8 the Conventional versus Laparoscopic-Assisted Surgery in Colorectal Cancer (CLASICC) trial (526 laparoscopic v 268 open)67; the Colon Cancer Laparoscopic or Open Resection (COLOR) trial, which had more than 600 patients in each group9; and the Barcelona trial, with around 100 patients in each group10—have compared laparoscopic surgery with open surgery for colon cancer. These trials demonstrated improved postoperative recovery, such as reduced use of drugs and shorter length of stay, in the laparoscopic cohorts, with similar rates of cancer recurrence, complications, and long term survival between open and laparoscopic groups.

However, laparoscopy has disadvantages. Tactile feedback is limited and tremors can be projected through the instruments, making delicate tissue handling challenging. Laparoscopic instruments are limited by 4° of motion, whereas the human wrist has 7° of motion. Hand to eye coordination is crucial because of the loss of depth perception, and the fulcrum effect—where the surgeon must move the instrument handle in the opposite direction to that in which he or she wants to move the working end—is also a challenge.11 Visualization and coordination can be difficult while simultaneously holding a camera, moving instruments, and watching a two dimensional monitor. Unlike in open surgery, the surgeon cannot look at his or her hands and the surgical field at the same time. In addition, improper positioning of the table height, monitors, and instrument ports can lead to back, joint, and muscular pain and injury.12

The challenges in laparoscopy may explain why, despite the advances in minimally invasive surgery in the past four decades, most colorectal operations in the US are still performed by the open approach.13 A large retrospective review of the US National Inpatient Sample (NIS) database looked at patients who underwent abdominoperineal resections for rectal cancer between 2009 and 2012.14 Of the more than 18 000 patients sampled, 69.5% had open surgery, 25.8% had laparoscopic surgery, and 4.7% had robotic surgery. Another review of the NIS database from the same time period looked at patients undergoing elective colectomies; of the 509 000 procedures performed, 52.3% were open, 46.2% were laparoscopic, and only 1.5% were robotic.15 At the time of this review, more than half of all cases of colorectal surgery in the US were being performed with open techniques as opposed to minimally invasive techniques. As might be expected, laparoscopic and robotic surgery are more often performed at larger high volume centers.1315

### Glossary

• ACOSOG: American College of Surgeons Oncology Group

• AESOP: automated endoscopic system for optimal positioning

• ALaCaRT: Australasian Laparoscopic Cancer of the Rectum Trial

• ASCRS: American Society of Colon and Rectal Surgeons

• BMI: body mass index

• CLASICC: Conventional versus Laparoscopic-Assisted Surgery in Colorectal Cancer trial

• COLOR: Colon Cancer Laparoscopic or Open Resection trial

• COREAN: Comparison of Open versus laparoscopic surgery for mid or low RErectal cancer After Neoadjuvant chemoradiotherapy non-inferiority trial

• COST: Clinical Outcomes of Surgical Therapy trial

• CRM: circumferential resection margin

• ECA: extracorporeal anastomosis

• ICA: intracorporeal anastomosis

• IIEF: International Index of Erectile Function

• NIS: National Inpatient Sample

• NOTES: natural orifice transluminal endoscopic surgery

• RCT: randomized controlled trial

• RHC: right hemicolectomy

• ROLARR trial: RObotic versus LAparoscopic Resection for Rectal Cancer trial

• RRICA: robotic right colectomy with intracorporeal anastomosis

• TAMIS: transanal minimally invasive surgery

• TME: total mesorectal excision

## Types of robotic models

Robotic surgery evolved from attempts to minimize the disadvantages of laparoscopy. One of the earliest robotic models developed in 1994, the automated endoscopic system for optimal positioning (AESOP), used a voice activated arm that held the camera, allowing for a stable image while the surgeon operated with two hands. In early 2000, the Zeus robotic surgical system (Computer Motion) combined the AESOP technology with robotic arms that were controlled at a separate surgeon console. This led to the development of the da Vinci surgical system, which is currently the most widely used robotic assisted surgical platform. The surgeon sits at a console to view a three dimensional high definition video feed. Ergonomically positioned hand controls and footswitch pedals are used to manipulate four robotic arms, which carry the instruments and the endoscope.16 The three dimensional high definition video feed allows for advanced optics and depth perception, and it eliminates the challenge of hand to eye coordination. The fulcrum effect in laparoscopy is eliminated because the movement of the instruments follows that of the surgeon’s hands in the console. The wristed instruments have 7° of motion and are modeled after the human wrist, allowing for improved dexterity. These features reduce the challenges of laparoscopic intracorporeal suturing. The accuracy and fluidity of movements allow for precise dissection, particularly in narrow spaces like the pelvis. Other features of the robotic system are the EndoWrist Stapler, the EndoWrist Vessel Sealer, and the integration of FireFly fluorescence imaging to help assess perfusion and identify vessels and other structures.17 These advantages may overcome the challenges that laparoscopy poses for colorectal procedures.

### Robotics versus laparoscopy

The indications for the use of robotics in colorectal surgery are the same as for laparoscopy. Robotics can be used in the treatment of any colorectal disease, such as malignant and benign tumors, diverticulitis, inflammatory bowel disease, colonic inertia, and rectal prolapse.181920 Similar to laparoscopy, the relative contraindications for its use include emergency surgery, inability to tolerate insufflation, uncontrolled bleeding, and poor visualization.21

The American College of Surgeons National Surgical Quality Improvement Program database was used to compare laparoscopic and robotic approaches in 11 477 patients undergoing colorectal surgery.22 Operative times were significantly longer when robotics was used (P<0.001), but length of hospital stay was significantly shorter (P<0.001). In patients undergoing pelvic surgery, the rates of conversion to open surgery were lower with robotic surgery (P=0.01), whereas patients undergoing abdominal surgery showed no significant difference in conversion rates. No significant differences were found in rates of surgical site infection, anastomotic leak, 30 day readmission, or 30 day reoperation.

A retrospective cohort study of the Michigan Surgical Quality Collaborative registry analyzed laparoscopic and robotic colorectal operations from 2012 to 2014.23 Of the more than 2700 minimally invasive cases analyzed, conversion rates and length of stay were significantly lower in the robotic group. No significant difference was found in rates of complications including surgical site infection, anastomotic leak, and 30 day readmission.

Two NIS databases of laparoscopic and robotic colectomies from 2008 to 200924 and 2009 to 201025 found no differences in overall complication rates or length of stay, but conversion rates were significantly lower in the robotic group (6.3% v 10.5%; P<0.001). However, a prospective analysis of a database from Singapore that compared a laparoscopic group, an open group, and a converted laparoscopic group found no differences in length of stay up to five years.26 Other retrospective studies have similarly shown no statistical differences in length of stay or time to return of bowel function.2728

### Robotic right colectomy

Laparoscopic right hemicolectomy (RHC), most often performed for cancers or tumors of the ascending or proximal transverse colon, is a relatively uncomplicated colorectal procedure with evidence supporting its feasibility, safety, and clinical and oncologic outcomes.293031 A retrospective review that compared 77 laparoscopic with 105 open right colectomies found that patients who underwent laparoscopic RHC had a lower median length of stay (5.5 days v 7 days; P<0.001) and similar rates of lymph node harvest (P=0.742) and overall survival (P=0.904) when compared with those who had undergone open right colectomy.32

Overall, current evidence shows that robotic assisted RHCs are safe and feasible.3334 A single institution RCT compared 40 robotic assisted RHCs with 135 laparoscopic RHCs and found no significant differences in lymph node harvest, estimated blood loss, conversion rate, length of stay, or incidence of complications.33 A systematic review and meta-analysis in 2014 included both randomized and non-randomized studies; seven studies (234 robotic RHCs and 415 laparoscopic RHCs) were included in the analysis.34 It found that the robotic group had significantly lower overall complications (mean difference 0.62, 95% confidence interval 0.42 to 0.92; P=0.02), faster return of bowel function (−0.79, −1.10 to −0.48; P<0.000001), and lower estimated blood loss (−18.79, −28.7 to −8.88; P=0.0002). There were no significant differences in conversion rate, length of stay, or anastomotic leak rates. An RCT, which was analyzed in the systematic review, equally randomized 70 patients at a single institution with right sided colon cancer to robotic or laparoscopic right hemicolectomy.35 No significant differences were seen in length of stay (7.9 days v 8.3 days), conversion rates (0 v 0), surgical complications (6 v 7), or quality of the pathologic specimens, although operative times were significantly longer (195 minutes v 130 minutes; P<0.001) in the robotic group. Overall, hospital costs in the robotic group were significantly higher ($8714 (£6536; €7313) v$5110; P=0.018).

### Robotic right colectomy with intracorporeal anastomosis

Extracorporeal anastomosis (ECA), which requires additional mobilization of the colon to exteriorize the bowel through a mini-laparotomy incision, is the most common method used to create an ileocolic anastomosis during a laparoscopic RHC. This is because the use of straight, non-articulating laparoscopic instruments makes a laparoscopic RHC with intracorporeal anastomosis (ICA) difficult and time consuming to perform.36 However, some studies have shown benefits of ICA over ECA in RHC, such as faster return of bowel function, shorter length of stay, and reduced use of drugs.37

Two retrospective reviews (n=86, n=50) compared the use of ICA versus ECA in laparoscopic RHC.3839 They found that laparoscopic ICA is feasible and safe, with no difference in postoperative complications such as rates of anastomotic leak, wound infection, or intra-abdominal abscess.

Robotic surgery, with its advantages of wristed instruments and a three dimensional image, in addition to the release of the Robotic EndoWrist Stapler, may help overcome the difficulty of performing ICA, while maintaining the benefits that have been shown for laparoscopic ICA. Two small single center retrospective reviews published in 2013 and 2015 reported their outcomes of 20 and 52 patients, respectively, who underwent a robotic right colectomy with intracorporeal anastomosis (RRICA). They found no conversions, intraoperative complications, or 30 day mortalities and concluded that RRICA is a safe and feasible approach.4041 Another retrospective review found that RRICA (n=89) was associated with shorter incision lengths, decreased rates of incisional hernias, and less estimated blood loss when compared with laparoscopic right colectomies with ECA (n=135).42

A large retrospective multicenter study of 236 patients found no significant difference in conversion rates, morbidity or mortality rates, or average number of lymph nodes harvested when RRICA was compared with laparoscopic right colectomy with ICA and ECA.43 In addition, RRICA showed significantly decreased time to flatus and shorter length of stay compared with laparoscopic right colectomies with extracorporeal anastomosis. At this time, no published prospective randomized trials have investigated the outcomes of RRICA. The current literature suggests that RRICA is safe and feasible but confirmation is needed from large randomized studies.

### Laparoscopic surgery in rectal cancer

Total mesorectal excision (TME) is the complete removal of the lymphatics and lymph nodes of the perirectal mesorectum. This crucial pelvic dissection is the standard of care in the surgical treatment of rectal cancer. Both the quality of TME and the involvement of the circumferential resection margin (CRM) are associated with rates of recurrence and long term survival.4445

To discuss the role of robotic surgery in the treatment of rectal cancer, it is important to understand the evidence on laparoscopy in rectal cancer (table 1). Its use has been controversial because studies have shown mixed results. The 2007 CLASICC trial was a large, randomized trial of 794 patients, comparing laparoscopic versus open surgery for rectal cancer.7 No significant differences were found between the laparoscopic and open surgery groups in the three year endpoints of overall survival, disease-free survival, or local recurrence.

Table 1

Studies on laparoscopic surgery in rectal cancer*

View this table:

The Comparison of Open versus laparoscopic surgery for mid or low REctal cancer After Neoadjuvant chemoradiotherapy non-inferiority (COREAN) trial randomized 340 patients at three centers in South Korea to open or laparoscopic surgery.4647 It found no significant differences between CRM positivity rates or quality of TMEs. Because the differences in three year disease-free survival (difference: −6.7%, 95% confidence interval −15.8 to 2.4; P<0.0001) did not exceed the pre-specified non-inferiority margin (15%), it was concluded that laparoscopic surgery, when performed by qualified surgeons, can result in non-inferior survival outcomes compared with open surgery.

Two large multicenter non-inferiority RCTs published in 2015, the Australasian Laparoscopic Cancer of the Rectum trial (ALaCaRT)48 and the American College of Surgeons Oncology Group (ACOSOG) Z6051 trial,49 assessed whether the laparoscopic approach for rectal cancer is non-inferior to open resection. The ALaCaRT trial of Australia and New Zealand randomized 475 patients with T1-T3 rectal cancer within 15 cm of the anal verge. Successful resection was measured by CRM, distal resection margin, and completeness of TME. The laparoscopic group did not demonstrate non-inferiority to the open group. The ACOSOG study randomized 486 patients with stage II or III rectal cancer less than 12 cm from the anal verge. Successful resection was assessed by laparoscopy but neither trial could establish non-inferiority of laparoscopic to open resection and the authors concluded that the evidence did not support the use of laparoscopy for rectal cancer. Whether these differences in pathologic outcome translate to poor long term clinical outcomes has yet to be established. Data are still being collected in both trials and secondary endpoints, such as local recurrence and disease-free survival, have yet to be reported.

### Robotic surgery in rectal cancer

With its wristed instruments for improved dexterity in narrow spaces like the pelvis, robotic surgery for rectal cancer has been promoted as an improved minimally invasive alternative to standard laparoscopy. The current literature comparing robotic, laparoscopic, and open resections for rectal cancer includes systematic reviews, meta-analyses, large retrospective series, and single center reviews. These studies compare endpoints including operative times, conversion rates, length of hospital stay, lymph node status, circumferential and distal margin status, quality of TME, complications, disease-free survival, urologic and sexual function, and local recurrence rates (table 2).

Table 2

Studies on robotic surgery in rectal cancer*

View this table:

#### Peri-operative outcomes

A large US national database review looked at 16 275 patients from the National Cancer Database who underwent robotic (n=956), laparoscopic (n=5447), or open (n=9872) low anterior resection.50 It found no significant differences between open versus laparoscopic surgery, or open versus robotic surgery in rates of positive margins, number of retrieved lymph nodes, readmission rates, or 30 day mortality. Laparoscopic and robotic surgery were associated with decreased length of stay compared with open surgery (P<0.001), and robotic surgery was associated with lower rates of conversion to open surgery compared with laparoscopic surgery (P<0.001).

A 2015 systematic review and meta-analysis included 2224 patients from 17 studies that compared robotic versus laparoscopic approaches for rectal cancer.51 It found that, compared with the laparoscopic approach, robotic surgery was associated with significantly lower rates of conversion (P<0.001) and decreased time to flatus (P=0.03). A systematic review and meta-analysis of seven studies with 1074 patients compared the safety and efficacy of robot assisted versus open surgery in rectal cancer.52 Robotic assisted surgery was associated with decreased estimated blood loss (P<0.00001), shorter length of stay (P=0.003), and shorter time to flatus (P<0.00001), but a longer operation time (P<0.0001). It found no differences in complications, distal resection margin, or disease-free survival between the two groups.

Another meta-analysis assessed 24 studies, including two RCTs, with 3318 patients, that compared robotic versus laparoscopic surgery for colorectal cancer.53 The robotic group had significantly lower rates of conversion. There was no difference in postoperative complication rates, distal resection margins, or costs. Although estimated blood loss and length of stay were lower in the robotic group, there was significant heterogeneity between the groups (P=0.000).

#### Sexual and urologic outcomes

Recovery of sexual and urologic function was also better in patients who had undergone robotic surgery compared with laparoscopic surgery for rectal cancer. A retrospective review with 40 patients in each group showed greater improvement of sexual function using the International Index of Erectile Function (IIEF) score at three and six months after robotic resection compared with laparoscopic resection (P=0.006 and P=0.016, respectively).51 A retrospective cohort study found similar rates of erectile dysfunction in both groups one month after surgery; however, one year after surgery function was completely restored in 100% of sexually active patients in the robotic group and only in 43% of sexually active patients in the laparoscopic group.54 A single center cohort study compared a prospective robotic group (n=69) with a retrospective laparoscopic cohort (n=69).55 It evaluated postoperative urinary function with the International Prostate Symptom Score (IPSS). The study found earlier return of urinary function at three months after surgery in the robotic group compared with the laparoscopic group (P=0.036). However, at one year, there were no differences in function between the two groups (P=0.827). Sexual function, as evaluated by the IIEF score, showed no significant differences between the two groups.

#### Oncologic outcomes

Matched cohort studies have also assessed whether robotic surgery provides good oncologic outcomes with regard to the quality of TME, rates of CRM positivity, and disease-free survival. A retrospective cohort study compared short term outcomes in 263 patients with rectal cancer who received robotic, laparoscopic, or open resection.56 It found no significant difference in the quality of TME or complication rates, whereas the laparoscopic and robotic cohorts had significantly decreased recovery time (P<0.05). A subsequent similarly designed matched cohort study compared robotic versus open and laparoscopic techniques for rectal cancer, with 165 patients in each group.57 Time to flatus, resumption of diet, and length of stay were significantly lower in the robotic and laparoscopic groups compared with the open group (P <0.001 for each). Rates of CRM involvement were also reduced in the robotic group compared with the open group (P=0.034), and no differences were seen in disease-free survival at two years between any of the groups. Another matched cohort study that compared patients undergoing robotic assisted TME with those who had undergone laparoscopic TME in the past found that the robotic group had significantly better CRM than the laparoscopic group (P=0.022) but no differences in the number of harvested lymph nodes (P=0.053).54

A more recent retrospective cohort study published in 2017 compared robotic versus laparoscopic resections and similarly found no significant difference in length of stay, overall morbidity rates, quality of TME, or rates of CRM positivity.58 Two retrospective studies that compared three year59 and five year60 overall survival found similar rates between robotic and laparoscopic cohorts.

An RCT in Korea evaluated TME quality and complication rates on the basis of a single surgeon’s experience in 113 patients who were randomized to robotic or laparoscopic resections.6164 It found no significant differences between the two groups in operative times, estimated blood loss, average lymph node harvest, distal resection margin, or CRM. Days to soft diet (P=0.008), length of stay (P=0.001), and conversion rates (P=0.013) were significantly lower in the robotic group than in the laparoscopic group. However, macroscopic TME grading was significantly better in the robotic group (P=0.033). This trial, where the average body mass index (BMI) was 23, has limited generalizability to the US, where patients have a much higher average BMI.

A single center RCT from India published in 2017 randomized 50 patients with rectal cancer to robotic or open surgery.62 Estimated blood loss was significantly less (P<0.001) in the robotic group than in the open group. Neither group had CRM positivity, however the mean distal resection margin (tumor-free margin measured distal to the tumor) was significantly longer in the robotic group (P=0.001). The robotic group had longer mean operative time (P<0.001) but significantly decreased length of hospital stay (P<0.001).

These studies from Korea and India are small with only short term follow-up but they are among the few prospectively randomized studies in the literature. Their results suggest that robotic low anterior resection can be performed safely and with good pathologic results. Current data suggest that robotic TME provides similar clinical outcomes to laparoscopic and open TME and can be an oncologically effective surgical approach for treating rectal cancer.54596365 However, larger prospectively randomized trials are needed to support its use.

The highly anticipated Robotic versus Laparoscopic Resection for Rectal Cancer (ROLARR) trial has recently been published. This international multicenter prospective RCT randomized 471 patients from 29 centers in 10 countries to robotic versus laparoscopic resections for rectal cancer.66 The primary outcome was the conversion rate, and the secondary outcomes included 30 day morbidity and mortality, CRM positivity, three year local recurrence rate, disease-free and overall survival rates, and sexual and urinary complications. The study found no significant difference in conversion rate (unadjusted risk difference 4.1, −1.4 to 9.6; P=0.16) between laparoscopic and robotic approaches. In addition, no significant differences were seen in CRM positivity, TME completion, rates of intraoperative complications, postoperative complications, or 30 day mortality. Subgroup analysis found an improvement in conversion rates in robotic versus laparoscopic surgery in men (odds ratio 0.455, 0.209 to 0.987; P=0.0429), and it has been suggested that robotic surgery may have greater benefit than laparoscopy in the narrower male pelvis. A limitation of the study is that the participating surgeons had a wide range of robotic experience (median experience of 50 robotic cases, interquartile range 30-101). This large multicenter study of surgeons with varying experience did not show a significant benefit of robotics over laparoscopy in the treatment of rectal cancer. Future studies of similar design should involve only surgeons with higher level experience.

### Obesity and minimally invasive surgery

Obesity is a growing epidemic in the US, with more than a third of adults having a BMI over 30.67 Surgery in obese patients is associated with postoperative complications such as deep vein thrombosis, cardiorespiratory complications, wound infections, dehiscence, incisional hernias, and anastomotic leaks.6869707172 Minimally invasive surgery has the advantage of decreasing the risk of these postoperative complications.72 However, laparoscopic surgery in obese patients is technically challenging and is associated with prolonged operative times and higher rates of conversion to open surgery.7071 Several retrospective reviews have shown that conversion to open laparotomy is associated with greater estimated blood loss, increased pain, more postoperative complications, longer operative times, and longer hospital stays.737475

Robotic assisted surgery and its advantages in dexterity, visualization, and surgeon ergonomics may help overcome the challenges of laparoscopy in obese patients. A small (n=90) retrospective case controlled study that compared obese (BMI ≥30) versus non-obese (BMI <30) patients undergoing robotic colorectal surgery found no difference in conversion rates, operative time, intraoperative or postoperative complications, or length of hospital stay.76

A larger (n=216) retrospective case matched study also compared obese (BMI ≥30) and non-obese patients (BMI <30) who underwent robotic colorectal surgery.77 It found no significant difference in operative times, conversion to laparotomy, estimated blood loss, or length of stay between the groups, although wound infection rates were significantly higher in the obese group. While these studies support the feasibility of robotics in obese patients, both are relatively small retrospective series that analyzed only robotic cases.

Current evidence on robotic surgery in obese patients is limited and prospective studies are needed to compare the outcomes between robotic, laparoscopic, and open approaches.

### Costs

One of the biggest criticisms of robotic surgery is its cost. The da Vinci surgical system is the only currently available surgical robot on the market, and it has a high upfront cost, ranging from $1 to$2.5 million per unit.78 The learning curve in robotic surgery must also be considered in the cost analysis. Several studies have shown that as a surgeon’s experience increases, operative times also decrease, which leads to reduced overall costs.78 A retrospective review of a single surgeon’s 85 consecutive robotic assisted rectal dissections from 2010 to 2012 analyzed the difference in operative times and direct hospital costs between the first 43 cases and the last 42 cases.79 The mean operative time was significantly lower in the latter group compared with the first. Direct hospital costs were lower in the latter group but this was not significant.

A similar retrospective study compared the costs of a single surgeon’s first 50 robotic versus laparoscopic rectal resections.80 The study also compared operative times and costs as a function of experience within the robotic group, separating the 50 cases into three phases: the initial learning curve (cases 1-19), the competent period (cases 20-40), and the experienced phase (cases 41-50). On average, the operative times and overall costs were significantly higher in the robotic group than in the laparoscopic group. However, operative times and costs were significantly reduced in the experienced phase robotic cases compared with the initial learning curve and competent phases. When fixed costs (costs of the non-disposable robotic instruments plus the purchasing and maintenance of the robotic system) were excluded, no statistically significant difference was seen between the laparoscopic group and the experienced phase robotic group. These studies suggest that as more surgeons surpass their learning curves and increase their annual caseload, robotic operative times should improve and overall costs should fall.

Some studies have found higher overall operating room costs and hospital charges for robotic cases compared with laparoscopic and open ones.15242581828384 However, operating room cost is not the only important factor when assessing the economics of robotic surgery; overall costs are also affected by length of stay, complication rates, and readmission rates.

A high volume single center retrospective review that compared 227 patients who underwent laparoscopic or robotic colorectal surgery found no significant difference in mean operating room times or mean hospital charges.85 A limitation of this study is that it did not include the fixed cost of the robotic system or costs per case in the analysis.

The contribution margin is the hospital revenue generated by a surgical case minus the costs of labor and supply during the hospital stay. Most of the cost of a hospital stay comes from postoperative care and is affected most by the length of stay. At our previous institution, Robert Wood Johnson Medical School at Rutgers University, we retrospectively analyzed the costs of robotic abdominoperineal resections and laparoscopic abdominoperineal resections between 2009 and 2013 as well as robotic cases for diverticulitis between 2010 and 2015.86 We evaluated the length of stay, contribution margin, costs, and profits of robotic colorectal surgery compared with laparoscopic and open cohorts.8788 Our results were presented at the 2015 and 2016 ASCRS conferences in Boston and Los Angeles. In our calculations of contribution margins and operating room costs, we incorporated the charge per case for use of the robotic system and the annual maintenance fees of the robot but not the purchase cost of the robot. Although the average operating room costs were significantly higher in the robotic group ($4859 v$3530; P=0.0006), this was offset by the significantly lower mean length of stay (3.9 days v 7.2 days; P=0.0032), making the average total hospital costs the same between the two groups ($21144 v$23149; P=0.073). The average contribution margin in the robotic group was higher than that in the laparoscopic group. The literature on robotic surgery and its costs is still conflicting. As shown in our review, the robotic approach to colorectal surgery has been associated with decreased length of stay as well as decreased readmission and complication rates.

With these improvements in clinical outcomes, the increasing expertise of surgeons in robotics, and efforts to reduce the fixed costs of the robotic surgical system, robotic surgery may prove to be the most cost effective approach. However, further investigations and cost analyses are needed to show this.

## Guidelines

Many studies support the notion that, with an experienced surgeon, the use of robotic colorectal surgery is safe, efficacious, and has similar outcomes to open and laparoscopic surgery. However, no guidelines are available on the use of robotic colorectal surgery because of the lack of clinical data to support a consensus. Robotics is a relatively new surgical approach—laparoscopy has been around for decades longer but there are still no guidelines on its use in colorectal surgery. In the surgical treatment of rectal cancer, guidelines on the quality of the resection (complete TME) are available,4445 but currently there are no guidelines as to which approach should be used to achieve this. The available data are promising, and as more surgeons gain experience in robotic surgery, future guidelines may arise from large prospective multicenter trials that establish a significant benefit of the robotic approach.

## Emerging treatments

### Single incision robotic surgery

Single incision laparoscopic surgery uses a multi-channel port in a single skin incision. It has been used in cholecystectomies and colectomies and has similar outcomes to multi-port laparoscopic approaches.89 However, single incision laparoscopic surgery has its challenges—clashing instruments and the inability to triangulate or articulate instruments result in poor ergonomics. The da Vinci Single Site System was developed to rectify some of these disadvantages, but its use is limited to single quadrant procedures with limited dissection, such as cholecystectomies.909192

The technique of single incision robotic colectomy using a GelPOINT port (Applied Medical) is described in the largest retrospective review of 59 patients.93 There were four conversions to open laparotomy, three conversions to multiport robotic laparotomy, and one conversion to single port laparoscopy. Conversions were caused by poor visualization, extensive adhesions, and malfunctioning equipment. Although this study, among other smaller case series,9495 has shown that the technique is feasible, further investigation is warranted.

To date, no published studies have compared single incision robotic colectomy with multi-port robotic or laparoscopic approaches, and no studies have assessed the oncologic outcomes with this technique. The da Vinci Sp Single-Port Robotic Surgical System is a platform in which wristed instruments and a flexible endoscope enter together through a 25 mm port and can articulate inside the abdomen. This device was recently approved by the Food and Drug Administration, but it has yet to be released to the market.

### Robotic transanal TME and TAMIS

Open, laparoscopic, and robotic TME are performed through a top-down dissection intra-abdominally. The transanal TME uses a bottom-up approach through the anus, which was developed to improve the quality and outcomes of TME in the treatment of rectal cancer.969798 It is a type of natural orifice transluminal endoscopic surgery (NOTES) that mobilizes the rectum using endoscopic and sometimes laparoscopic techniques. Initial small studies comparing transanal TME with laparoscopic TME have shown that this modality is feasible,99100101 and that it can yield longer CRMs, with lower rates of positive CRMs and better quality of TME.3496102103 A robotic assisted transanal TME is being developed. In this approach, robotic trocars are placed through a single incision laparoscopic surgery port, such as the GelPOINT, which is inserted transanally. Several pilot studies have shown the feasibility of this approach.104105106107108109

Transanal minimally invasive surgery (TAMIS) is a relatively new approach to endoluminal excisions of benign or early rectal tumors.107 Similar to the transanal TME approach, a single incision laparoscopic port is placed in the rectal vault and standard laparoscopic instruments are used to resect benign rectal polyps or early stage rectal cancers. Transanal endoscopic microsurgery is an older approach introduced in 1983 in which rectal lesions are excised through an operating proctoscope. Both TAMIS and transanal endoscopic microsurgery have been shown in retrospective reviews and systematic reviews and meta-analyses to be safe and feasible, although transanal endoscopic microsurgery has the disadvantages of higher costs and a steeper learning curve.110111112113114115116117 Like any single incision laparoscopic procedure, TAMIS still has its challenges, such as colliding instruments, torque forces causing leakage of insufflation, and the lack of articulating instruments. Robotic TAMIS was described in 2011, when it was carried out on a cadaveric model.107 To date, only small case series and case reports have demonstrated the feasibility of robotic TAMIS for the local excision of rectal tumors.118119120

Robotic assisted transanal TME and TAMIS are both novel methods being studied for the treatment of rectal tumors. Future large RCTs are needed to investigate the short term and long term clinical and oncologic outcomes in addition to the cost-benefit of these approaches. The advantages of the robotic articulating instruments and improved optics in combination with a NOTES approach may prove to be an emerging technique in the future of robotic surgery.

## Conclusion

Minimally invasive approaches have been shown to improve outcomes in colorectal surgery. Studies have shown shorter hospital stays, less pain, faster return to work, decreased risks of postoperative complications, better cosmesis, and decreased rates of surgical site infections with laparoscopy compared with open methods. However, because laparoscopy is challenging and conversion rates are still high, most cases of colorectal surgery are still performed by the open method.13

Robotic surgery has advantages over laparoscopy in terms of articulating instruments, advanced three dimensional optics, surgeon ergonomics, and improved accessibility to narrow spaces such as the pelvis. The use of the robotic approach has been studied in a range of colorectal procedures and compared with laparoscopic and open approaches. Conversion to laparotomy has been shown to be associated with a higher risk of complications and longer hospital stay. The current literature shows that, compared with laparoscopy, robotic surgery is associated with decreased rates of conversion to open laparotomy. Studies have shown that the robotic approach is safe and feasible in a wide range of colorectal procedures, with no difference in clinical or oncologic outcomes when compared with laparoscopic and open approaches. However, more research is needed in the field of robotics. Most of the literature comprises retrospective studies with short term follow-up, and although initial results are promising, there is no overall proof that robotics is superior to laparoscopic or open methods. The recently published ROLARR study did not show significant benefit of robotic surgery over laparoscopic surgery in rectal cancer. However, the surgeons in the study did not have uniformly high levels of experience in robotic surgery. Multicenter prospective randomized trials that include surgeons who are increasingly experienced in robotic techniques are needed to evaluate the benefits of robotic colorectal surgery. As colorectal surgeons use robotics more and surpass their learning curves, operative times and procedure costs are expected to decrease. Future cost analyses are warranted. The role of robotics in colorectal surgery will become more clear as interest and research in robotic surgery continue to grow.

### Questions for future research

• Is robotic surgery superior to open and laparoscopic surgery in obese patients?

• Is there an advantage to robotics in male patients?

• Does robotic surgery provide equivalent or non-inferior pathologic and long term clinical outcomes compared with open surgery?

• Will there be an effect on operative times and the costs of robotic surgery as surgeons surpass their learning curve?

## Footnotes

• Series explanation: State of the Art Reviews are commissioned on the basis of their relevance to academics and specialists in the US and internationally. For this reason they are written predominantly by US authors

• Participators: CLC performed the research and wrote the paper; CR supervised the research, helped with content and editing, and is guarantor.

• Competing interests: We have read and understood BMJ policy on declaration of interests and declare the following interests: none.

• Provenance and peer review: Commissioned; externally peer reviewed.

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