Essay: Medical robotics—a bright future

Abstract

The history of medical robots, though short, has required much creativity. Since their launch just over 20 years ago, the robotic systems that have been used clinically have evolved substantially. The basic rules and approaches to the use of robots in medicine had to be invented. For example, industrial robots were not intended for use near people, so the whole strategy to ensure the safety of patients and medical personnel had to be worked out from fi rst principles. As in the early days of computing, much of the early promise of medical robotics failed to materialise; only recently have more reliable, better targeted, clinical implementations achieved medical and commercial success. The earliest use of robots in medicine was to hold a fi xture at a specifi ed location and orientation next to the head, so that a surgeon could manually conduct neurosurgical procedures. Subsequently, modifi ed industrial robots were used for hip and knee replacement orthopaedic surgery. Because the leg could be rigidly clamped in position, the bones could be machined in a similar way to a computer numerical control manufacturing process. The cutter was positioned by the surgeon at a desired location, and the robot autonomously carried out the procedure in accordance with a preoperative plan based on CT of the leg. The surgeon had no further part to play other than to hold an emergency off button. Two examples of this type of robot were the Robodoc (ISS, USA) and Caspar (URS, Germany). Both companies ended up in liquidation, for complex reasons. However, in August, 2006, a Korean company (Novatrix Biomedical Inc) invested in Robodoc. As a result, the company is back in business, and an application is being made in the USA to fi nalise approval for Robodoc by the Food and Drug Administration. Early implementations of medical robotics were diffi cult because engineers needed to have a very precise specifi cation of the task. Surgeons, however, are trained in an apprenticeship system, which places little value on precise measurement of displacements, velocities, and forces. Thus, engineers had to visit the operating room and infer the measurements of physical parameters they thought appropriate to a procedure. This very iterative and time-consuming task was necessary to ensure that the design of the robotic system was correct and that the task was universally recognised as one diffi cult to carry out manually, justifying robotic implementation. Although universities can research medical robotics relatively easily in the laboratory by means of industrial systems, clinical application is very much more demanding. My own fi rst experience of clinical implementation of a medical robotic system was for transurethral resection of the prostate in 1991. This was the fi rst time that a robot was used actively to remove tissue from a human patient. The robot was designed with a special-purpose framework that constrained cuts to the desired region and which could also hold an ultrasonographic measurement system that provided a preoperative plan. This autonomous robot could be positioned at the veru montanum and automatically remove tissue while the surgeon had no further part to play other than hold an emergency off button. Although surgeons had thought that this feature was desirable, their unease with being observers of a procedure that was largely in the control of the robot programmer soon became apparent. Subsequently we developed a new type of specialpurpose robot for orthopaedic surgery called the Acrobot, which stands for active constraint robot, in which the robot actively constrains the surgeon to cut accurately within a safe region. It was designed as a hands-on robot, in which a force-controlled handle is placed near the end of the robot arm. The handle is held by the surgeon and moves around under servo-control to compensate for friction and gravitational forces. It has been developed into a system that can accurately achieve minimally invasive surgery, for example for unicondylar knee replacement. Randomised clinical trials have shown that the robot can achieve much better accuracy for this procedure than experts using conventional jigs and fi xtures. The evidence on use of a robot for total knee replacement is less clear, since many surgeons say that they have no diffi culty in achieving the required alignment accuracy. However, even for this less demanding procedure, a large number of revisions Brian Davies is Professor of Medical Robotics at Imperial College of Science, Technology and Medicine, London. He is also founder and Technical Director of the Acrobot Company Limited, which was a spin-off from his research at Imperial College.