Single-port Robotic Transanal Total Mesorectal Excision in a Porcine Model (Sus scrofa domesticus)

Summary

This protocol demonstrates Single-port (SP) robotic transanal total mesorectal excision (taTME) in a porcine model, highlighting procedural feasibility, technical steps, and preclinical applicability for minimally invasive rectal surgery.

Abstract

This study presents a step-by-step protocol by using a robotic system for performing SP robotic transanal total mesorectal excision (taTME) in a porcine model. The goal is to evaluate the feasibility, procedural characteristics, and immediate postoperative outcomes of this novel approach. Compared to conventional laparoscopic and robotic systems, this technique offers potential advantages in maneuverability and visualization within the narrow pelvic space. This protocol involves sequential abdominal and transanal phases, providing clear guidance for surgical preparation, robotic docking, dissection, specimen retrieval, and anastomosis. The study includes ethical considerations and detailed intraoperative management to ensure reproducibility. Representative results demonstrate successful rectal resection without intraoperative complications. The total operative time was 140 min, including 25 min for robotic docking, 45 min for the abdominal phase, 35 min for transanal dissection, and 35 min for anastomosis and closure. Estimated blood loss was approximately 10 mL. This protocol utilized the SHURUI SP robotic system, with a dual-continuum snake-like arm design offering enhanced dexterity and instrument control in confined anatomical spaces. The described method establishes a standardized and reproducible preclinical framework, serving as a valuable platform for technical training, advanced device testing, and the refinement of SP robotic taTME protocols prior to clinical translation.

Introduction

Minimally invasive surgery has revolutionized rectal cancer treatment by reducing surgical trauma and improving postoperative recovery. TaTME provides excellent access to the deep pelvis and improves the visualization of distal resection planes^1,2. However, conventional laparoscopic taTME is limited by suboptimal ergonomics, restricted instrument mobility, and a steep learning curve within the narrow pelvic cavity³.

Recent robotic surgical systems have been developed to address these challenges and have shown promising applications in colorectal surgery^4,5. While single-port (SP) platforms like the da Vinci SP reduce invasiveness, they remain expensive and rely on articulated instruments composed of rigid links and joints. These conventional designs typically depend on single-cable actuation, where the breakage of one cable causes the entire instrument to fail, offering no actuation redundancy.

In response, the SHURUI Endoscopic Surgical Robotic System was developed to overcome these mechanical limitations (Figure 1). Unlike rigid-link systems, this system features a unique dual continuum mechanism (Snake-like arm) that utilizes redundantly arranged super-elastic nitinol backbones to achieve motion via continuous deformation. This design not only enables a tight bending wrist for superior intra-abdominal dexterity but also enhances payload capability and safety through actuation redundancy, ensuring the system remains functional even under stress. This protocol demonstrates the application of the system for robotic taTME in a porcine model, aiming to assess procedural feasibility and establish a standardized workflow.

Protocol

All procedures involving animals were approved by the Institutional Animal Care and Use Committee of Daping Hospital, Army Medical University (Approval No. 2024(325)). The study was conducted in compliance with national and institutional guidelines for the care and use of laboratory animals.

1. Preoperative preparation

1. Acquire a healthy female pig (Sus scrofa domesticus) weighing approximately 65 kg from a licensed laboratory animal supplier. Confirm health status with an official veterinary health certificate.
2. Fast the animal for 12 h before surgery, allowing free access to water.
3. Administer premedication via intramuscular injection of atropine (0.02 mg/kg) to reduce secretions. Induce general anesthesia using a tiletamine–zolazepam injectable anesthetic (1:1 combination, 0.08 mL/kg) intramuscularly. Following endotracheal intubation, maintain anesthesia with 1.5%–2% isoflurane inhalation. Administer prophylactic antibiotics intravenously during the procedure.
4. Place the animal in the supine position on the operating table. Disinfect the abdominal, perianal regions, and the rectal lumen using povidone-iodine solution.
5. Insert a urinary catheter to prevent bladder injury during pelvic dissection.

2. Robotic abdominal phase

1. Create a 3–4 cm periumbilical incision and insert the SP access device into the abdominal cavity.
2. Establish pneumoperitoneum at 12 mmHg with CO₂ insufflation. Confirm successful port placement by the ability to maintain a stable 12 mmHg pneumoperitoneum throughout the abdominal phase.
3. Dock the SP robotic system to the access device, positioning it perpendicular to the operating table on the left lateral side. Configure the four instrument arms as follows: Arm 1 for bipolar dissecting forceps, Arm 2 for grasping forceps, Arm 3 for the endoscope, and Arm 4 for monopolar electrocautery scissors (Figure 1). The docking configuration during the abdominal phase is shown in Figure 2A.
4. Begin abdominal exploration to confirm no unexpected lesions or abnormalities.
5. Identify the inferior mesenteric artery (IMA) and skeletonize the vessels, performing a lymphadenectomy along the root of the IMA. Exercise caution with electrocautery to minimize thermal spread to surrounding tissues.
6. Clip and divide the IMA distal to the origin of the left colic artery (LCA), preserving the LCA to maintain adequate blood supply to the proximal colon.
7. Mobilize the sigmoid colon and descending colon by dissecting along the mesocolic plane.
8. Perform pelvic dissection following the mesorectal plane down to the level of the peritoneal reflection.

3. Robotic transanal preparation

1. Prior to incision, perform a perianal local infiltration block using a long-acting anesthetic to ensure adequate postoperative analgesia. Use the referenced surgical retraction device to establish circumferential anal retraction and optimize surgical exposure.
2. Insert a lubricated transanal port. Disinfect the rectal lumen using povidone-iodine-soaked gauze followed by irrigation with diluted povidone-iodine solution.
3. Place a circumferential purse-string suture approximately 5 cm proximal to the anal verge to occlude the rectal lumen. The purse-string is confirmed to be successful when complete occlusion of the rectal lumen is achieved, preventing intraluminal contamination during subsequent proctectomy (Figure 2B).
4. Prior to pneumorectum insufflation, thoroughly irrigate the distal rectal lumen with sterile saline to remove debris and residual povidone-iodine solution.
5. Insert a customized SP transanal access platform into the anal canal.
6. Establish pneumorectum with CO₂ insufflation at 12 mmHg. Successful transanal port placement is confirmed by achieving a stable pneumorectum at 12 mmHg and clear endoscopic visualization of the distal rectal lumen.
7. Dock the robotic system to the transanal access port. Assign the instrument arms as follows: the first arm to the bipolar dissecting forceps, the third to the endoscope, and the fourth to the monopolar electrocautery hook.

4. Robotic transanal phase

1. Perform a full-thickness circumferential proctectomy 0.5–1.0 cm distal to the purse-string suture.
2. Enter the mesorectal (holy) plane and initiate bottom-up dissection.
3. Dissect posteriorly along the avascular plane toward the sacrum.
4. Continue lateral dissection, carefully preserving the neurovascular bundles.
5. Proceed anteriorly, separating the rectum from adjacent pelvic structures.
6. Extend dissection cranially toward the peritoneal reflection.
   NOTE: The dissection is confirmed to be complete at the point where the mesorectal (holy) plane dissected from the transanal route successfully connects (rendezvous) with the plane mobilized during the abdominal phase.

5. Specimen retrieval and anastomosis

1. Extract the resected rectum and mesorectum transanally through the access port (Figure 2C).
2. Inspect the resection margins to confirm completeness.
3. Prepare the proximal colon for anastomosis.
4. Perform a hand-sewn coloanal anastomosis under direct visualization using interrupted absorbable sutures (Figure 2D).

6. Closure

1. Remove the transanal port and ensure hemostasis in the pelvic cavity.
2. Desufflate the abdomen and remove the abdominal port.
3. Close the abdominal incision in layers using absorbable sutures for fascia and skin.
4. Remove the urinary catheter.
5. Upon completion of the surgical procedure, while the animal is still under deep general anesthesia, humanely euthanize the animal via an intravenous overdose of pentobarbital sodium (100 mg/kg). Confirm absence of heartbeat and respiration to verify death.

Results

No significant operational problems or hurdles were encountered during the use of the SHURUI SP robotic system, and no notable intraoperative adverse events occurred. The estimated blood loss was approximately 10 mL. The total operative time was 140 min, comprising 25 min for docking, 45 min for the transabdominal phase, 35 min for the transanal phase, and 35 min for anal anastomosis and closure. These findings provide preliminary evidence supporting the feasibility and safety of performing taTME using the robotic system...

Discussion

The successful implementation of SP robotic taTME in a porcine model demonstrates the feasibility and technical reliability of this approach. Several critical steps are essential to ensuring procedural success. Accurate placement of the transanal purse-string suture is fundamental to prevent intraluminal contamination during the proctectomy. Similarly, maintaining a stable pneumorectum is crucial for optimal visualization and precise dissection within the confined pelvic space^6,

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Lone Star Retractor System			surgical retraction device
SHURUI single-port robotic system	Beijing Surgerii Technology Co., Ltd., China	SHURUI SP (SR-ENS-600)	The Shurui single-port robotic surgical system is a novel robotic platform designed for minimally invasive surgery through a single incision. It's known for its snake-like arms and continuous deformation mechanisms, potentially offering advantages in wound appearance and flexibility compared to traditional multi-port robotic surgery or single-incision laparoscopy.
STARport	Shinaide, Xiamen, China		modified single-port robot-assisted transanal minimally invasive surgery platform