Article - Issue 58, March 2014
Robots in theatre
Professor Brian Davies FREng
Doctors at St Mary’s Hospital in Paddington carried out a world first in June 2013 using a surgical robot to tackle a common cause of infertility in women, fibroids, or non-cancerous growths in or around the womb. Interventional radiologists were able to treat fibroids in five patients without complications by blocking the blood supply. Dr Mo Hamady, using the Magellan robotic system master, controls the position and force of a catheter. The left screen shows a 3D view of the anatomy and the right screen shows a view of the catheter as it approaches the fibroid © Imperial College Healthcare NHS Trust
Professor Brian Davies FREng, Emeritus Professor of Medical Robotics at Imperial College London, was the inventor of the surgical robot, PROBOT, which in April 1991 became the first in the world to remove tissue from a living human being. He writes for Ingenia about the current state of robotic surgery, and assesses its future prospects.
Recent years have seen surgical robots scoring a number of successes in the operating theatre. Most notable are their roles in radical prostatectomy (the partial removal of a cancerous prostate gland), and accurately positioning replacement joints in orthopaedic surgery. In spite of intensive research and development over the past two decades, the number of robotic procedures in routine use is still small. Why so? If robots are good for the tasks mentioned, it might be thought that they could equally be applied in operations on the lungs, the liver, the kidneys and, indeed, every other organ in the body.
Despite many claims that robotic surgery would soon be widely performed, even in the absence of a surgeon, this has not come about. Real achievements have turned out to be, in most respects, more modest. So, what are the possibilities for surgical robots, and what is holding back their more widespread use?
Autonomously following the surgeon's plan, the robot prepares the surface of the upper end of the femur, and then reams out a space inside it to ensure a perfect fit when the surgeon comes to insert the shaft of the implant.
Working with robots
Broadly speaking, there are three ways in which surgeons can work with robots. First, they can use computerised tomography (CT) or other forms of 3D imaging to locate the target tissue and plan the operative procedure on a computer. Once the appropriate instructions have been delivered to the robot, it can execute the task autonomously with the surgeon acting simply as an observer, ready to step in if anything goes wrong – see An autonomous robot.
The second method of working is by telesurgery based on a master/slave relationship in which the robot performs the operation, but does so in response to a surgeon manipulating a set of controls housed in a remote console with a viewing screen. In this case, the surgeon still controls the actions of the instruments relative to the patient’s organs, albeit indirectly – see Telesurgical robots.
The third type of robot is a hands-on system in which the surgeon holds and manipulates the end of the robotic arm bearing the tool, but is confined by the robot to working within a predetermined region of the patient’s body – see Hands-on robots.
An Autonomous Robot
Designed for use in hip and knee joint replacement, the Robodoc® was one of the first surgical robots to enter the market. In 1992, it made medical history as the first of its kind to be used on humans, assisting a surgeon in a total hip arthroplasty procedure. It has been used in over 25,000 joint replacement procedures worldwide.
The surgeon chooses a suitable artificial joint for hip replacements, having first consulted a computer image derived from a CT scan of the upper end of the patient's femur. The surgeon manoeuvres images of this implant and of the patient's bone on a computer screen to give the best fit. The robot then receives the relevant positional data.
In the theatre, the surgeon exposes the patient's joint, anchors the leg bone to avoid movement, and advances the robot's rotating cutting ball towards the joint surface. Autonomously following the surgeon's plan, the robot then prepares the surface of the upper end of the femur, and reams out a space inside it to ensure a perfect fit when surgeon comes to insert the shaft of the implant.
Surgeons practice using the ‘da Vinci’ robotic surgical system. It is often used to resect cancer from the prostate using minimally invasive laparoscopic incisions, while ensuring continued prostate function © Intuitive surgical
This branch of robotic work grew out of minimally invasive laparoscopic (keyhole) surgery in which instruments are inserted into the patient's body cavity through three or four small incisions. In the case of telesurgery, however, the instruments are operated not by the surgeon but by a robot.
The surgeon sits at a remote console and views the tips of the instruments and the target tissue on a screen connected to a 3D endoscopic camera. Controls mounted on the console allow the surgeon to perform the operation remotely, but with the versatility and dexterity that would be expected in conventional hands-on surgery.
The da Vinci® machine made by the Intuitive Surgical has proved to be the most popular of this type of robot for radical prostatectomy. The da Vinci has four spider-like arms, controlled by the surgeon, which hold cutting instruments to make tiny incisions and remove the prostate or cancerous part using images from the telescope to guide the surgeon. Evidence shows that using these robots means significantly less blood loss, reducing the need for blood transfusion and probably leading to shorter overall recovery times.
Another simpler telemanipulator, Hansen Medical's Sensei X robot, is designed to control catheter movements in robot-assisted treatment of atrial fibrillation, one of the most common causes of heart arrhythmia. It has been used in more than 10,000 patients already, according to Hansen. Surgeons control a robotic arms to place a catheter in the patient's heart atria, guided by a 3D navigation system, with a master system that also controls the forces applied.
The Acrobot system used clinically for unicondylar knee surgery. A ball-ended cutter is attached to the draped robot, while the leg position is tracked with a passive arm. In the background, a display shows the cutter position and the tibia, with colours denoting the stages of cutting © B Davies
A hands-on robot is one in which the surgeon holds the end of the robot arm adjacent to the interventional tool. The surgeon can manipulate the tool only within a region previously defined using computerised scans. The robot stops the surgeon cutting outside this area.
The arrangement provides synergy between surgeon and robot, with the former using his or her experience in performing the procedure, and the latter providing accuracy and safety by confining interventions to the chosen region.
Examples include the Acrobot ® orthopaedic robots which the author helped develop in the early 1990s, the name deriving from ’Active Constraint Robot’. Designed for replacing one of the knee condyles, this robotics system used CT-scans to obtain data for pre-operative planning. During the operation, the robot applies resistive force to the surgeon’s hand based on the defined surgical region. The use of active constraints confines the surgeon’s actions to the safe region and assists the surgeon to achieve accurate cuts and trajectories. Mako Rio acquired Acrobot Technology in April 2013 and was in turn acquired by Stryker in December 2013.
Popularity of robotic surgery
Few surgeons are enthusiastic about the autonomous systems. Many feel that a machine operating at their command but not under their moment-by-moment control has the effect of sidelining them in their own theatres. For that reason, the Robodoc is one of only a few such machines now commercially available.
The Acrobot hands-on robot is mounted on a trolley and has pitch, yaw and in/out powered motions. At its end it carries a high-speed ball-ended cutter mounted on a passive orientation device. A separate passive arm independently tracks the patient’s knee bone, updating the robot’s safety constraints if the patient moves © B Davies
Telesurgical robots are more popular, particularly for urological procedures. Their emergence followed that of laparoscopic minimally invasive surgery (MIS) with its virtues of smaller wounds, less scarring, less pain and shorter hospital stays. In non-robotic MIS, the surgeon operates using long-handled tissue manipulators that can variously grip and snip and are inserted into whichever body cavity - often the abdomen - houses the target organ or tissue.
In the hands of experienced and skilled laparoscopists, the results can be excellent. However, the problem with instruments of this kind is that they are relatively cumbersome, deny surgeons their normal wrist articulation, create problems of eye-hand coordination and in other ways inhibit normal manual dexterity.
In addition, it takes surgeons up to 30 procedures to acquire the skill needed to use the robotically manipulated instruments via a telesurgery console. Its advantage is that it sidesteps the main drawbacks of conventional MIS. Controlled by the surgeon with a 3D view of the operating site, the robotic slave can use more versatile instruments that replicate wrist movements, eliminate hand tremor and offer motion scaling for very fine work. The slave’s tools are mounted on tubular structures. Fine wires inside the tubes are driven by electric motors outside the body to control the actions of the tools.
Unless the target tissue can be securely anchored, as in Robodoc, robotic systems need some method of coping with any movement that may occur during the procedure. Hands-on systems such as Acrobot use a mechanical arm lightly pinned to the patient’s bone to detect any movement and make compensating real-time adjustments to the position and path of the cutting tool.
Telesurgical systems rely on surgeons themselves responding to what they can see. More sophisticated arrangements are emerging, as in the case of efforts to allow robots to work on rhythmically moving tissue, such as the heart. One technique under development tracks the motion of the heart using an endoscopic camera and feeds the information back to a mechanism that moves the instruments on the same axis and to the same rhythm. To surgeons viewing a stabilised image of the scene, it appears that the robot under their control is operating on a target that remains motionless.
Normally, when using any handheld instrument, we rely on sensory feedback to judge the rigidity of the material being worked, and the pressure being applied. When direct contact with a tool is lost, as it is in laparoscopic or robotic surgery, so too is this feedback. Attempts have been made to simulate it. Thus far, a surgeon operating by conventional open body methods has more sensitivity to pressure or small anatomical differences, even through rubber gloves, than can be provided by any existing technology designed to mimic these sensations. The da Vinci robot has almost no force feedback; it relies on good 3D vision. The Hansen Sensei X robot uses a sophisticated force-sensing master to indicate the force exerted by its slave. Clues about the pressure being applied to soft tissue can also be inferred from the visual appearance of structures being deformed - but it takes much practise to acquire the necessary skills.
The technology of the visual imagery used in telesurgical systems is far more advanced. This has the advantage of a sophistication born of R&D carried out over a long period for all sorts of other unrelated purposes. Better tactile sensing remains a major research topic, and is now generating encouraging results.
Many of the barriers to the wider clinical use of robots lie not in the technology but in the broader context. The costs of robotic systems, not only capital but cost per procedure, are high and need to be justified by clearly demonstrated benefits. The translation from R&D into products available for clinical use is also proving difficult. Recent legislation has made the move from early prototype to ‘first in man’ trials lengthier and more costly. Venture capital funds have been difficult to obtain, particularly with the threat of patent litigation from large aggressive competitors. Even when such litigation has no validity, contesting it can cost millions. Domination by a few large companies with big patent portfolios is helping to fuel a move away from large complex robots to simpler, lower-cost devices specific to a few tasks.
Part of a process
While the robots themselves are the most eye-catching element of robotic surgery, they constitute only one part of a process. They are dependent on other technologies, including the computer systems with which surgeons plan their operations. For orthopaedic robots especially, good image registration is crucial. Preoperatively, using 3D CT scans, the surgeon chooses the ideal position for a selected joint replacement, so allowing the computer to map the coordinates of the volume of tissue to be removed. During the operation, the robot uses these coordinates to achieve perfect registration, or alignment, between the scope of its actions and the surgeon’s plan of the target tissue. A variety of methods of effecting good registration are available. In the case of hard tissue, these may exploit details of the surface morphology, or specific anatomical landmarks or cone-shaped artificial markers inserted into bone.
Safety is of paramount importance, especially in autonomous systems, and the emergency off-switch is self-evidently an absolute necessity. But hands-on systems too need arrangements for avoiding accidental damage. Hence the importance of the firm resistance that will be encountered by a surgeon attempting to move the electrically powered cutting tool of the Acrobot beyond a pre-determined safe region. An alternative method of achieving the same end is the NavioPFS system which uses a cutting tool with a retractable burr. When the surgeon approaches the margins of the safe zone, the burr is automatically retracted into a protective sleeve.
Uncertain evidence of benefit
The benefits of robotic surgery have yet to be backed up by a substantial body of evidence. The cost-effectiveness of a robotic system is determined not by the extent to which the engineers and surgeons hit their own short-term targets, but by how far this success offers longer-term clinical advantage to the patient. In the case of partial, unicondylar knee replacement, an error of no more than 2o of misalignment (which robotic surgery achieves) is considered an excellent result, while one of 6o would probably cause problems.
What is not clear is the point at which misalignment is clinically significant. It takes years of follow-up to demonstrate lasting success, and requires measurements such as leg length, range of movement and the ability to climb stairs. But even these apparently objective metrics are not entirely satisfactory, not least because different patients may have different innate capacities to adapt to imperfect surgery.
Something similar is also true of telemanipulator procedures. Robotic surgery for prostatectomy causes less blood loss and is less likely to result in impotence or incontinence than open procedures. However, so far it has not been possible to demonstrate that it gives better results than the non-robotic laparoscopic approach in skilled hands. And that term ‘skilled hands’ is a factor to be borne in mind when assessing any new surgical procedure. There is a learning curve when starting to use these techniques, and no assessment is fully fair until the surgeon has done the operation 25-30 times – or even more, according to some.
Radical prostatectomy by robot is undoubtedly popular, not least with patients. Some now insist on it, even where a skilled laparoscopist is available. Having purchased costly and complex robots, hospitals and their suppliers are naturally exercised to find new applications, not all of which can be justified by improved outcomes.
Recent increases in litigation, primarily on the basis of poor outcomes resulting from inadequate robotic training, dictate caution in predicting further progress. Current trends towards simpler, smaller, lower-cost systems limited to tasks that the surgeon finds difficult imply that large complex robots are unlikely to represent the future and will gradually be superseded. Throughout all surgical procedures, better planning, sensing and assessment are leading to a new understanding of the critical features to be achieved and how robots can help.
Challenging surgical tasks continue to exercise an irresistible fascination for imaginative biomedical engineers. The heart, the womb, the spine, the cochlea and the retina are among the areas that have attracted the interest of medical robotics researchers. Several groups are investigating the potential of snake-like devices to reach parts of the body that would be difficult or even impossible to access without this degree of hypermobility. A system being developed at Imperial College, for example, uses a tube built up of short articulated subsections powered by tiny motors. Its flexibility is such that it can even turn back on itself.
Returning to currently available systems, the benefits of robotic surgery in its accurate targeting of defined volumes of tissue, its precision in performing (or helping the surgeon to perform) intricate work, and its value in handling repetitive work have to be weighed against a clutch of drawbacks. These include a high capital cost, extra staff, additional training and increased set-up and/or operating times. The position of the cost-effective tipping point remains uncertain.
The short history of robotic surgery has already witnessed a move away from autonomous systems and towards what might more accurately be described as multi-sensor intelligent tools. Surgeons are becoming reassured that they need have little fear for the future; robots seem likely to extend rather than diminish the role of the human surgeon.
Emeritus Professor Brian Davies FREng was Professor of Medical Robotics at Imperial College London. He started research into surgical robots in 1988 and has researched a number of applications, including that of a unicondylar orthopaedic robot in 1992. He then formed the spin-off company Acrobot Ltd to provide the UK’s only commercial clinical surgical robot system. He is currently involved in a number of UK and EU robotic research projects.
The author would like to thank Geoff Watts, science and medical writer and broadcaster, for his help in writing this article.