Flexible Robotics

Robotic technology is being increasingly used for a variety of surgical procedures. This article describes some novel flexible robotic platforms that may enhance the capabilities of flexible endoscopy and provides a rationale for robotic technology’s further development and future use. It also reviews some recent experimental and clinical usages of flexible robotic technology to perform ureterorenoscopy and to provide treatment of stones.

The initial foray into the use of robotics in urology began with transurethral resection of the prostate. However, robotics in urology truly came into its own with the application of robotics to assist in laparoscopic surgery. The initial application of robotics in laparoscopy was the use of a voice-controlled robotic arm as a responsive and accurate camera holder (Aesop, Computer Motion). This was followed by the development of more complex surgical robotic systems that operated on the master–slave principle (Zeus, Computer Motion; da Vinci, Intuitive Surgical). The development of the Zeus system was halted after Intuitive Surgical acquired Computer Motion in 2003.

The da Vinci system is a currently available, widely used surgical robotic system that features wristed instruments with increased degrees of freedom, three-dimensional visualization with depth perception, motion scaling, and elimination of tremor. Although the da Vinci system is a rigid, master–slave surgical manipulator designed and used for laparoscopic applications, recently several flexible robotic systems have been introduced primarily for intravascular catheter-based applications. In this article, the authors describe these novel flexible robotic platforms, review the initial experimental and clinical applications for flexible endoscopy, and postulate possible future roles for the platforms in performing single-port laparoscopic and natural orifice transluminal endoscopic surgery (NOTES).

The need for flexible robotics

With miniaturization and refinement in fiberoptic and endoscopic technology, endoscopic imaging of myriad bodily viscera through a multitude of natural orifices has become routine, and almost every body cavity is now accessible to some form of endoscopic inspection and manipulation. Despite significant progress, currently available endoscopic equipment continues to have limitations inherent to the manual control of endoscopes and their effectors. The ability to have fine control of the effector tip of flexible endoscopes and flexible catheters and to maintain these devices in a stable position in three-dimensional body cavities may be limited when using manual control. Using manual steering technologies for flexible endoscopes that provide navigation within a three-dimensional body cavity requires experience and expertise because moving the tip to a specific location requires a combined insert, roll, and articulation input that is complex and somewhat arbitrary. Additionally, the long duration of many procedures exposes the physician to considerable amounts of x-rays and the risk of nonergonomic strain. Despite these limitations when using manual endoscopes, the experienced endoscopist can perform a wide variety of diagnostic and therapeutic procedures.

Thus, there may be an advantage in developing a computer-controlled robotic platform that allows precise, controllable, complex, and reproducible maneuvers of flexible endoscopes inside hollow organs and three-dimensional anatomic spaces to further enhance the capabilities of manual endoscopy. Such a system should facilitate surgical manipulation within these complex spaces, thus transferring the advantages of a rigid robotic system into the endoscopic environment.

Two other philosophically similar but technically different, emerging areas have prompted renewed interest in flexible robotics. One such area is the use of NOTES, which involves traversing intact hollow viscera (eg, stomach, vagina, rectum, bladder) to access intra-abdominal organs for ablative or reconstructive surgery. The instrumentation required to accomplish NOTES through various natural orifices is in evolution; clearly, additional work needs to be done. Safe, reliable, and reproducible techniques for foolproof visceral closure remain undefined. Whereas the tubular, hollow viscera are generally amenable to conventional endoscopy, NOTES will require far more complex movements in the peritoneal cavity, including complex retraction and suturing maneuvers. It is in this role that robotic platforms may provide an advantage in facilitating the performance of NOTES procedures.

The other emerging area is single-port laparoscopic surgery, or laparoendoscopic single-site surgery (LESS), which is a term recently coined to describe various techniques that are used to perform laparoscopic procedures through a single skin incision, which is often concealed within the umbilicus. With currently available technology, the major limitations with LESS include the lack of triangulation of the closely situated instruments that are clustered together at the common entry point and the limited retraction and countertraction for heavy intra-abdominal tissues and organs. Although the current da Vinci system has been used for robot-assisted NOTES and LESS procedures, challenges still remain from the clashing of the robotic arms and the instruments, which result in reduced range and precision of motion. Dedicated robotic platforms with a smaller profile or with steerable, flexible effector arms are likely to help circumvent these issues and make these procedures easier and more reproducible.

Flexible robotic systems

Initially developed for cardiovascular applications, including endocardial ablation for arrythmia, Hansen Medical, Inc. (Mountain View, CA) has adapted a flexible robotic catheter system to be used for performing ureterorenoscopy. The robotic catheter consists of a remote master–slave control system ( Fig. 1 ) consisting of: (1) a console for the surgeon, including an LCD display and a master input device (MID); (2) a steerable catheter system; (3) a remote catheter manipulator (RCM); and (4) an electronics rack. At the workstation, three adjacent LCD monitors display endoscopic, fluoroscopic, and other applicable procedure-specific imaging. The MID is a three-dimensional joystick that the surgeon uses to remotely manipulate the catheter tip, whose movements mimic those of the surgeon’s hand. The steerable catheter system ( Fig. 2 ) has two components: an outer catheter sheath (14/12 Fr) that is manually inserted and an inner catheter guide (12/10 Fr) through which the steerable catheter is inserted and manipulated remotely. That the workstation can be positioned at a distance from the patient serves to limit radiation exposure to the surgeon.

Another commercially available flexible catheter manipulator system (NIOBE II, Stereotaxis, Inc.) uses a computer-controlled magnetic field for catheter steering. This system employs computer-controlled magnets placed on opposite sides of the patient, which create a magnetic field within which a catheter with a magnetic tip can be remotely steered with great accuracy. A motor is used to advance or retract the catheter, thus allowing for remote navigation. Manipulation of the catheter tip can be made in 1-mm increments with 1° of deflection. Recent improvements in the Stereotaxis system allow for integration with three-dimensional mapping software and image integration (eg, MRI) that can potentially decrease x-ray exposure to the patient by minimizing the need for real-time fluoroscopy. For cardiac ablative procedures, the external magnets are aligned with the patient’s chest. Because a small magnet is embedded in the tip of the catheter, this system necessitates the use of specific, custom-designed catheters. When the outer magnets change their relative positions, the magnetic field is altered, thereby affecting tip deflection. The magnetic field sequences can be stored and played back to automate certain maneuvers. As with any remotely controlled system, the Stereotaxis system allows the physician to be protected from fluoroscopic radiation by being away from the operative field. The Stereotaxis system has been used predominantly for cardiac applications, and to the authors’ knowledge has not been used for nonvascular endoscopic applications.

Multiple remotely controlled flexible catheters, instruments, and scopes also have the potential to be combined inside a common channel. Separate devices could be positioned at independently desired locations to create necessary triangulation from a common entry point. The EndoVia System is one such system that incorporates independently controlled right- and left-hand effectors that are robotically controlled along with a flexible endoscope. Such a system, when refined further to achieve clinical applicability, has the potential to provide much greater control and capability for flexible endoscopy. In fact, preliminary experimental studies demonstrated that the ability of the EndoVia system to assist physicians in performing complex tasks, such as suturing, that are not possible using current flexible endoscopes. These enhanced flexible robotic systems could also provide the necessary triangulation, degrees of freedom, and tensile strength so that physicians can perform complex intra-abdominal procedures within a compact yet robust platform for NOTES and LESS procedures. Whether the use of the electromechanical or magnetic systems, a combination of the two, or some other configuration not yet conceived will be the ultimate solution remains unknown and a subject of speculation.

Flexible robotic systems

Initially developed for cardiovascular applications, including endocardial ablation for arrythmia, Hansen Medical, Inc. (Mountain View, CA) has adapted a flexible robotic catheter system to be used for performing ureterorenoscopy. The robotic catheter consists of a remote master–slave control system ( Fig. 1 ) consisting of: (1) a console for the surgeon, including an LCD display and a master input device (MID); (2) a steerable catheter system; (3) a remote catheter manipulator (RCM); and (4) an electronics rack. At the workstation, three adjacent LCD monitors display endoscopic, fluoroscopic, and other applicable procedure-specific imaging. The MID is a three-dimensional joystick that the surgeon uses to remotely manipulate the catheter tip, whose movements mimic those of the surgeon’s hand. The steerable catheter system ( Fig. 2 ) has two components: an outer catheter sheath (14/12 Fr) that is manually inserted and an inner catheter guide (12/10 Fr) through which the steerable catheter is inserted and manipulated remotely. That the workstation can be positioned at a distance from the patient serves to limit radiation exposure to the surgeon.