Abstract
To assess the current state of robot-assisted urological surgery, the literature concerning surgical robotic systems, surgical telemanipulators and laparoscopic systems was reviewed. Aspects of these systems pertaining to maneuverability were evaluated, with a view to quantifying their stability and locomotive properties and thereby determining their suitability for use in assisted laparoscopic procedures, particularly robot-assisted laparoscopic urological surgery. The degree of maneuverability and versatility of a robotic system determine its utility in the operating room, and the newer-generation surgical robotic systems have been found to possess a higher degree of maneuverability than older class 1 and class 2 systems.
It is now clearly established that robots have an important place in the urologist's armamentarium for minimally invasive surgery; however, the long-term outcomes of several urological procedures (other than robot-assisted radical prostatectomy) performed with the da Vinci surgical robotic system have yet to be evaluated.
Introduction
Robotic surgery evolved in an era of technically cumbersome laparoscopic surgery with its associated steep learning curve. The difficulty faced by laparoscopic surgeons in negotiating this learning curve led to the evolution of robotics Citation[1]. In 1985 an early industrial robot, the PUMA 560, was first put to clinical use in CT-guided needle brain biopsy, and in 1988 the PROBOT™ (Imperial College, London) was used in prostate surgery. In 1992 the ROBODOC™ (developed by Integrated Surgical Systems, Inc., Sacramento, CA) was used for precise bone cutting of the femur in hip replacement procedures, and subsequent robots evolved with increasing power and maneuverability in order to perform intricate surgical tasks. Following the 2003 merger of the companies that had developed the competing ZEUS™ Robotic Surgical System and da Vinci™ Surgical System (Computer Motion, Goleta, CA, and Intuitive Surgical, Inc., Sunnyvale, CA, respectively), the ZEUS system was phased out and the da Vinci system emerged as the leading master-slave surgical robotic system, having progressed from experimental use to clinical applications Citation[2].
The real benefits of robotic surgery stem from the enhanced surgical precision, miniaturization of the incision, diminished blood loss, reduced pain, and more rapid convalescence. Other advantages of robotic-assisted laparoscopic surgery are the possibility of articulation beyond the normal limits of the human wrist and three-dimensional stereoscopic vision with higher magnification. The advantages of robot assistance with regard to many ablative and reconstructive uro-surgical procedures are too numerous for urologists to ignore, and some of these are discussed later in this review. However, the long-term benefits of robotic assistance in urological laparoscopic surgery (other than in robot-assisted radical prostatectomy) and the associated cost-utility issues remain to be ascertained.
Classification and evaluation of surgical robots
Maneuverability
One dictionary definition of maneuverability would be the ability to make a series of changes in direction and position for a specific purpose. In surgical terms, this quality may be defined as the ease of making planned error-free motion(s) in all possible surgically intended planes, directions and degrees of motion. This can be quantitatively gauged by the index of maneuverability Citation[3], which has been previously described in the literature as a means to quantify and analyze locomotion and the degree of dynamic stability of a device Citation[4]. The quantitative index of maneuverability is based on the concept of ideal repetitive responses; it simply implies that the operator can maneuver the system as though they were directly attempting to manipulate a remote object across an obstacle by themselves Citation[5].
Classification of robots on the basis of maneuverability
The following three classes of robot have been described in the literature Citation[6], Citation[7]. This classification appears to be motivated, in part, by safety considerations, and is based on the robots’ design, maneuverability and degree of autonomy.
Class I robots: These are discrete passive robots. The robotic arms are unactuated and lack any autonomy whatsoever. They are basically conventional manipulators that possess the lowest degree of maneuverability.
Class II robots: These are semi-active robots, in which the power supply to the arms is curtailed or cut off during critically demanding tasks so as to limit their motion in certain restricted or delicate organs/anatomical spaces within the patient. The arms may be serpentine in nature, and the range of motion is extended by means of an increase in the number of discrete joints. These manipulators function as an arrangement of a small number of serially connected links and actuated joints. While effective at performing a number of tasks, they are still limited by their lack of maneuverability and in terms of the total number of degrees of freedom (DOF).
Class III robots: These robots are active devices with all joints being actuated and intrinsically capable of performing one or more parts of planned or assigned tasks. Simply put, these are “continuum robots”. They possess no discrete joints or rigid links; instead, the manipulator is capable of bending continuously along its entire length in a manner akin to a biological appendage (such as an elephant's trunk or octopus tentacle) that actually possesses 32 actuated degrees of freedom, and thus possess a maximum degree of maneuverability with a much larger number of degrees of freedom. To actuate the serpentine continuum motion, these class III robots use pneumatics, cable or spring, or fluid capsule actuations.
Surgical robots have been broadly divided into (a) image guided and (b) surgeon-driven systems Citation[8]. Those in the former category use a system to pinpoint the target previously identified by the surgeon on an image guidance system, while those in the latter category use the surgeon's inputs in a continuing fashion, translating them into an appropriate instrument manipulation with motion scaling and tremor filtering. Min and colleagues Citation[9] also designed and tested a new method of locomotion for robotic endoscopes intended to facilitate their safe maneuverability within the human gut. This consisted of an actuating mechanism composed of a solenoid at each end of the actuator and a single permanent magnet in the center guide. (This approach was based on the physics principle that if controlled periodic current is applied to two solenoids, attractive and repulsive forces develop between the magnet and solenoid). According to Canes and colleagues Citation[10], with the recent introduction of natural orifice transluminal endoscopic surgery (NOTES), flexible endoluminal or in vivo robots and progressive miniaturization of robots (with a fixed base, magnetic anchoring and guidance systems), it is predicted that some of the above problems associated with the use of standard laparoscopic and endoscopic instruments, such as the lack of a secure platform, impaired orientation, and incomplete maneuverability of the instrument tip, will be substantially overcome in the near future.
To improve instrument tip maneuverability, Degani et al. Citation[11] have also described a “highly articulated robotic probe” (HARP) with conventional actuation for experimental use in cardiac surgery. They reported that this probe could traverse a tight space without upsetting the contiguous viscera, allowing the surgeon to approach inaccessible intra-pericardial locations directly and perform controlled interventions with immense maneuverability.
The ideal uro-surgical robot
A perfect medical robot should be adapted so that it can operate advanced devices both within and outside the human body, and in such a manner that it is able to safely and reliably interact with the human interface, so as to improve health care and ultimately the patient's overall quality of life. A robot adapted for assisting in surgery should be intrinsically safe and reliable, have minimal redundancy, and be able to perform the assigned task accurately and repeatedly without error or causing hazards. Here, intrinsic safety refers to the inherent design of the medical robot and its mechanical arms; reliability refers to the innate ability of the robotic device to perform the assigned task repeatedly with the same degree of accuracy; redundancy refers to the duplication of critical system components to make the system more reliable and/or to ensure its fail-safe behavior; and hazards refers to the potential risks or harmful events arising from the interaction of the medical robot when deployed in the human environment. The hazard levels may vary from little or no potential for injury to minor injury potential to potential for causing disability and mortality in humans. While higher levels of redundancy tend to make a system more complex, they may also reduce its reliability; thus, ideal active medical robotic systems must guarantee safety without compromising their reliability and redundancy Citation[12]. We believe that an ideal surgical robot should be modular in design and lend itself to safe positioning at the urologist-patient interface in such a manner as to overcome most of the constraints imposed on the urologist by traditional rigid laparoscopic instruments. The robot should also be capable of being safely deployed within a restricted anatomical space such as the pelvis, retro-peritoneum or pediatric abdomen.
Technical aspects of robotics
Aspects such as dexterity, accuracy, reliability, repetitiveness, tremor-free movements, kinematics, high degrees of motion, and planes of vision are essential considerations when making any computer-assisted motion for surgical procedures. The degree of maneuverability available in robotic-assisted laparoscopy, as compared to manual laparoscopy, appears to overwhelmingly favor the use of the former approach, especially in terms of physician ergonomics. This is chiefly on account of the overall superior robot dexterity and the predictably precise robotic movements, with high reliability and repeatability, whereas manual laparoscopic movement is prone to errors due to surgeon hand tremor or fatigue and the limited degrees of freedom. Similarly, the superior kinematics of robotic arms, compared to the cumbersome movements of pure laparoscopic instruments, also contribute to the superior maneuverability attainable with robotics in laparoscopy. With regard to planes of motion, robots offer a greater number of planes of movement than are available in manual laparoscopy. Likewise, robotic arms fitted with EndoWrist™ instruments (Intuitive Surgical, Inc.) offer seven degrees of freedom, versus only three or four with conventional laparoscopic instruments, and allow an extended range of mobility. Another factor that contributes to the higher degree of maneuverability with robotic systems is the provision of 3D magnified stereoscopic vision provided by the dual 3-chip digital cameras available with the da Vinci Surgical System. The addition of such stereoscopic 3D vision may compensate for the lack of tactile/haptic feedback perception and sensation in several surgical scenarios.
According to Guilloneau Citation[13], surgical robots are surgical tools with the ability to operate on patients with an automatized gesture that is more precise and reproducible for each patient, being related to the specific anatomy and disease of the patient, with the goal of the modern surgical robot being to assist and improve the technique(s) of urological surgery. In general, however, “human haptic perception” and measures to increase its transparency Citation[14] appear to be lacking at present, and this remains an area of relative concern as it may have an impact on performance measures, especially in the context of bilateral tele-operation Citation[15]. It is believed that this concern is probably minimized with the availability of magnified stereoscopic imaging with no time-delay factor and an associated increase in the degrees of freedom of modern surgical slave-manipulator-based robotic systems.
Maneuverability in traditional manual laparoscopy
Manual laparoscopy, with its two-dimensional vision, fails to provide the much-needed third dimension to the laparoscopic surgeon. The limited maneuverability with conventional laparoscopy arises from a combination of factors: (i) the highly limited DOF (as few as three); (ii) the motions being prone to transmission of the surgeon's tremors and also being susceptible to the effects of surgeon fatigue; (iii) the necessity of operating against the background of a restricted, flat 2D view that lacks significant magnification; (iv) the lack of tactile/haptic feedback; (v) the unwieldy nature of long laparoscopic instruments; (vi) the significantly longer learning curves involved, especially for making minute, precise articulate controlled movements (such as when performing intracorporeal anastomosis/suturing) within a restricted space; and (vii) the overall inferior ergonomics as compared to pure laparoscopy.
Benefits of robotic maneuverability
Robotic or computer-assisted motion (CAM) is motorized assisted power movement that allows for computer-controlled surgical manipulation. Robotic instrument designs and accessories continue to evolve, and have enabled a high degree of delicate maneuverability, even within confined spaces such as the pelvis. This has been facilitated in part by the availability of Advanced 3D Vision Control (AVC)-based systems that have allowed robotic-assisted surgery to be performed on patients at locations far removed from the surgeon's own institutional operating room (tele-robotics). The real benefits in terms of patient comfort include (i) precise dissection and accurate suturing due to the availability of AVC- and CAM-based systems that appear to translate into superior surgical function/results; (ii) the elimination of surgeon tremor by the “filtering” process in CAM, which contributes to meticulous surgical gestures; (iii) the provision of a comfortable environment (console) for the surgeon that eliminates fatigue, thereby improving overall surgical outcomes; and (iv) superior ergonomics (motion scaling) of the robotic arms. All of these translate into significantly lower operating room times, negligible blood loss, shorter hospital stays for the patients, and shorter learning curves for the surgeon.
Applications of robotic maneuverability in urology
With the availability and commercial deployment of the da Vinci™ Surgical System, several successful uro-surgical procedures have been performed by urologists in the United States and elsewhere. The da Vinci™ surgical robot is well suited to use within the narrow confines of the bony pelvis, where a range of ablative as well as reconstructive robot-assisted laparoscopic urosurgical and uro-gynecological procedures can be performed successfully Citation[16]. Other surgical robot systems are being evaluated for potential application to urological surgical procedures, including retrograde intrarenal surgery (retrograde ureterorenoscopy) Citation[17], trans-urethral resection of the prostate (TURP) and targeted percutaneous renal access Citation[18], radiological interventions Citation[19] and image guided percutaneous procedures Citation[20]. Recently, the use of MRI-compatible robots in prostate biopsy and brachytherapy has also been reported Citation[21]. According to Stoianovici Citation[22], robots will eventually evolve to assist urologists with TURP, percutaneous renal access, laparoscopy and brachytherapy. summarizes the various types of surgical robot that have been developed, organized according to whether the systems are passive (having no intrinsic motion/energy) Citation[23], semi-active/synergistic (possessing some autonomous motion coupled to the surgeon's motion) or active (capable of totally motorized independent motion)/master-slave (motorized motion under the surgeon's control) robots. LARS™ Citation[24], Acrobot™ Citation[25] and NeuroMate™ Citation[26] are examples of semi-active robots, while AESOP™, EndoAssist™ Citation[27], ROBODOC™ Citation[28], CyberKnife™ Citation[29] and PROBOT™ Citation[30] are examples of active robot systems. A recent study Citation[31] suggested that both AESOP™ and EndoAssist™ are useful for providing timely, stable and consistent camera movements to facilitate complex laparoscopic procedures. Prototype master-slave robotic systems function as with kinesthetic coupling devices that enable the operator to maneuver the system as though the operator were directly manipulating the remote object Citation[32].
Table I. Broad classification of surgical robotic systems.
The modern da Vinci™ surgical robotic system comprises a remote console (master control with joysticks), a patient cart (with 3–4 robotic arms) and an InSite® Vision System, all of which combine to provide a highly coordinated, tremor-free, scaled motion resembling the articulations of the human wrist. The benefits of the modern master-slave surgical robotic system include increased range of motion and better instrument maneuverability/stability/ergonomics as compared to the traditional rigid instruments Citation[33]. The current da Vinci S HD Surgical System (Intuitive Surgical, Inc.), with its 3D high-definition vision can provide twice the effective viewing resolution with better clarity. The digital zoom function reduces interference between the endoscope and instruments, and the integrated touch-screen monitor permits telestration for improved proctoring and communication within the surgical team. The TilePro™ multi-input stereo viewer (Intuitive Surgical, Inc.) enables simultaneous display of multiple video inputs on the surgeon's console, integrating display of the patient's ultrasound, CT, MRI and intraoperative ultrasound images. This may be particularly beneficial in procedures like robot-assisted partial nephrectomy. However, a randomized controlled trial is needed to reliably establish the precise utility of TilePro™ in specific robot-assisted urological procedures. Extended-reach instruments are currently available for broader access, with an increased range of motion and a higher working volume Citation[34].
The successful global ingress of surgical robots is well established in several uro-surgical procedures and further expansion appears inevitable.
Robot-assisted radical prostatectomy (RARP) is one of the most widely performed uro-surgical ablative-cum-reconstructive procedures. Our recently published review of global RARP series predicted that in 2010 up to 70% of radical prostatectomies in the United States will be performed with robotic assistance Citation[35]. It appears that the “trifecta” of cure in RARP may be achieved early on with well-established functional and oncological outcomes Citation[36]. The critical benefits of using the da Vinci Surgical System™ in radical prostatectomy are magnified 3D vision, ease of peri-prostatic dissection with preservation of erectile function, simplicity of vesico-urethal anastomosis, negligible blood loss and rapid convalescence.
Robot-assisted partial nephrectomy (RPN) is another ablative-cum-reconstructive procedure that is an effective and minimally invasive surgical alternative to laparoscopic partial nephrectomy, especially for early stage T1 renal neoplasms. In our recent review of 350 global cases of RPN Citation[37], RPN was associated with acceptable initial renal functional outcomes and minimal complications in expert hands. The real benefits of robotic assistance in RPN appear to be related to the robustness of the robotic device in facilitating accurate renorraphy and in ensuring reliable hemostasis.
Robot-assisted radical cystectomy (RARC) Citation[38] and lymphadenectomy Citation[39] with preservation of the uterus/vagina in female patients Citation[40], extracorporeal reconstruction Citation[41], or robot-assisted intracorporeal neobladder-urethral anastomosis Citation[42] for urothelial cancer are challenging, complex urological procedures that nevertheless appear to be feasible, and have been successfully attempted at select centers where they may have replaced laparoscopic radical cystectomy Citation[43]; however, the precise benefits of such procedures are not yet well established in the literature Citation[44], Citation[45].
Robot-assisted pyeloplasty (RAP) for secondary and primary ureteropelvic junction (UPJ) obstruction with or without pyelolithotomy has also been successfully attempted with the da Vinci™ Surgical System. Our recent review of a global series of approximately 740 cases of RAP concluded that the initial peri-operative results and intermediate follow-up of cases of repair of the UPJ obstruction with RAP appear to be favorable and comparable to those obtained with open pyeloplasty Citation[46]. The chief benefits of RAP appear to be the accuracy, relative ease and faster pace of laparoscopic suturing when using robotic assistance.
Robot-assisted surgery within the narrow confines of the bony pelvis facilitates both ablative and reconstructive procedures (such as cystectomy, ureterolysis, ureteric re-implantation, repair of genitourinary fistulae, colposuspension, and sacrocolpopexy); in select patients, robot-assisted surgical outcomes for several uro-surgical procedures appear to be relatively better than those obtained with open and purely laparoscopic surgical procedures Citation[16].
Current drawbacks of robotic systems
The demerits of modern master-slave surgical robotic systems such as da Vinci™ include the need to accommodate the bulky hardware in the operating room, where space is already at a premium; the lack of tactile/haptic feedback sensation; the need to undock and re-dock for patient repositioning Citation[47]; and the high initial acquisition costs, along with the recurring cost of associated consumables Citation[48]. Additionally, the robot is a mechanical device that can malfunction. Robot malfunctions may be classified as temporary (recoverable and capable of being electronically overridden) or critical (non-recoverable and thus necessitating a system shut-down or outage), resulting in the robotic assistance having to be aborted. In a large-scale multi-institutional evaluation of robotic equipment malfunction (in more than 8000 robotic-assisted prostatectomies), Lavery and colleagues Citation[49] found that the robotic components that most commonly experienced critical malfunctions were the optics (34%) and robotic arms (34%), followed by the masters (10%) and power supply (15%), and then unknown components (7%), with an overall critical malfunction rate of approximately 0.4%. Other investigators have also reported the incidence of robotic malfunctions requiring conversion or postponement of the case to be 0.5–4.6%, and have suggested that at high-volume centers the availability of an additional or stand-by robot and a spare camera, together with more attentive servicing, may enable recovery from a critical malfunction or system outage, thereby further reducing the chances of a malfunction necessitating conversion to an open procedure Citation[31], Citation[50–54].
In a comprehensive review of the ZEUS™ and da Vinci™ systems Citation[55], Adonian and co-workers reported an overall estimated device failure rate (using the FDA MAUDE database) of 0.38% (189/50,000), with 21 and 168 malfunctions for ZEUS™ (in the period 2001–2003) and da Vinci™ (in the period 2000–2007), respectively. They also reported that the incidence of open conversion due to malfunction of the robotic device decreased from 94% in 2003 to 16% in 2007, and that 9 (4.8%) of the 189 reported device malfunctions were associated with patient injury.
Conclusions
We believe that robot assistance in laparoscopic urological surgery tends to improve the surgeon's level of dexterity and the degree of maneuverability. However, while the place of surgical robots in the urologist's operating room seems to be well established for minimally invasive urological procedures, the actual long-term patient benefits and limitations – if any – are yet to be determined. Further advances in the design and miniaturization of robotic systems will expand the range of potential applications of this exciting technology, but long-term trials and cost-benefit analyses will ultimately be necessary to define its precise role in the years to come.
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