Surgical robot dependability : propositions and examples

Surgical robotics is a domain where the robot has to interact with human beings in order to treat patients in a very constrained working environment; therefore dependability cannot be ignored. In this paper, we discuss some requirements of this specific domain, and based on the “dependability on design” principle, we propose several directions for improving safety, reliability and man/machine interaction. This discussion will be illustrated by several on-going projects. 1. Introductive discussion Computer-Assisted Surgery (CAS) is aimed to help the surgeon in the accurate, safe and efficient realization of minimally invasive interventions. The access reduction to the organs makes the perception of the surgeon more limited and his actions more difficult and less dexterous. This is why sensors and a priori information are introduced for better planning and action monitoring and guiding systems enable the surgeon to transfer an accurate pre-planned strategy to the operating site and to realize it safely and accurately. Classical taxonomies in CAS distinguish three categories of guiding systems : active, passive and semi-active systems. In this division, the degree of passivity corresponds to the type of interaction between the surgeon and the device. Passive systems such as [1,2] display information to the surgeon about the position of the surgical tool relative to anatomical data or to a pre-planned strategy. The surgeon is totally responsible for the execution of the surgical action. Active systems realize a part of the intervention autonomously. A robot may machine a bone, or hold a sensor or a surgical tool without the need for interaction with a human operator who generally supervises the action. See for instance [3]. A semi-active system involves a combined action with the human operator for the complete realization of the task. Such a system basically constrains the surgeon actions using a dedicated hardware. For instance, a mechanical guide brought in position by a robot [4] or manually [5] may align a linear drilling trajectory that the surgeon will execute. Another type of systems has been introduced more recently : Tele-robotic systems for which the surgeon remotely controls a surgical tool held by a robot (see for instance [6]). These systems are somewhat difficult to classify in the three categories listed below since the master and slave manipulators involve different types of interaction. Orthopedics is the surgical domain where robots were developed and pushed to the market most rapidly. The typical application is bone machining for cavity preparation when a prosthesis (hip or knee) has to be installed. This type of application is rather close to a manufacturing problem and the idea of using a robot to improve the cavity accuracy came naturally. Industrial robots were therefore modified to fit the domain constraints. However, about two decades after the first demonstrations, robots have not yet invaded the surgical operating rooms as it was predicted at that time. There are probably several reasons for that. First, having products in the medical domain may be very long and expensive as it is for drug introduction to the market. There are several development stages; as in many domains, the robot has to be developed to fit the application requirements and evaluated. The evaluation ranges from laboratory technical experiments quantifying accuracy, robustness, etc. to clinical experiments through a continuum : with phantoms, isolated organs, cadavers, animals, healthy volunteers (when the application makes it possible) and finally with patients. Clinical evaluation means that the system developers have to prove in close collaboration with clinicians from several hospitals, that the developed system has some clinical added-value and does not result in some extracomplications, accidents, excessive blood-loss or operating time, etc. as compared to conventional reference techniques. This clinical evaluation with patient follow-up for several months up to 1 A phantom is an artificial object reproducing as accurately as possible an organ or a part of the body. several years is very strictly regulated and requires application to ethical committees (CCPPRB in France). [7] is a very interesting reporting of such a product development from the very first research ideas to provisional clinical conclusions and to still open questions about the system clinical added-value. The second reason for a rather limited use of robots in surgery is, from our point of view, related to the real difficulty of introducing a robot in a surgical operating room for everyday clinical practice. This is due to the machine complexity and size, and to its generally limited userfriendliness. Price is also most likely a limiting factor. For many clinical applications, passive systems which are simpler and cheaper that robotic ones, are perfect tools : this also contributed to keep robots out of the operating rooms. The surgical use of robots could probably be amplified by improving robot dependability. 2. Surgical robot dependability Surgical robotics is different from industrial robotics from which it got its inspiration and many of its prototypes, in several points: Human beings – at least the patient, and most often the medical staff – are in the workspace of the robot. For some interventions, the risk is potentially very high : for instance when a cutting tool has to be operated by the robot very close to critical structures which damage could have dramatic consequences. 2 Comité de Consultation pour la Protection des Personnes dans la Recherche