Simulateur collaboratif de chirurgie d'instrumentation du rachis scoliotique en realite virtuelle avec interface haptique logicielle

The general objective of this research consisted in elaborating the software prototype of a collaborative virtual reality scoliosis instrumentation surgery simulator, including force feedback for the main corrective surgical manoeuvres, as an alternative training and learning tool. We stated two hypotheses. The first hypothesis was that the main corrective manoeuvres of scoliosis instrumentation surgery can be modeled and simulated in immersive virtual reality with a software haptic interface and a patient-specific biomechanical model at +/-15 % of the actual force values as perceived by expert surgeons. The second hypothesis was that a multirate haptic rendering loop, based on a prediction / correction algorithm, will achieve the minimal required update rate (1000 Hz) for a functional force feedback in a realistic training context.;The maximal forces during the rod rotation manoeuvre simulated for four scoliotic patients matched the few data available in the literature. The prediction / correction algorithm led to a haptic update rate surpassing the minimal rate required for a haptic interface. The simulated force profile evaluated by expert surgeons showed a global realistic appearance with slightly inferior values compared to forces applied in the operating room. We also demonstrated that the simulator was fully functional for geographically distant participants and that in a relatively short time, two users on different continents could collaboratively, with mixed equipment, complete a predetermined surgical scenario for scoliosis surgical training on a specific patient. These results allowed us to confirm the second hypothesis and partially confirm the first one.;Scoliosis instrumentation surgery is a new application for a medical haptic system because of its distinctive characteristics. This research project differed from other surgical simulators due to its integration of a complex patient-specific biomechanical model into a virtual reality immersive environment with a realistic software interface. From a complex physical model, unfit for haptic rendering, we developed a software haptic interface fast enough for real-time haptic system control. Our research allowed for a better use of virtual reality technologies and for a better visualization of scoliosis surgery. We have laid the foundations for a quantitative validation of the haptic forces obtained from the biomechanical model by expert surgeons. (Abstract shortened by UMI.);To test these hypotheses, our methodology included a modular client - server software architecture (developed in previous work) composed of three main entities: a collaborative biomechanical server, a telepresence multi-user server, and a virtual reality simulation client able to run on a standard PC as well as on a CAVE-like immersive environment system. We implemented a software haptic interface for the central corrective manoeuvre, the rod rotation. The haptic modelling on the server side relied on an adapted version of a complex patient-specific biomechanical model from a surgical planning tool, and the haptic rendering on the client side relied on a prediction / correction algorithm inside a multirate rendering loop to compensate for time delays mainly due to computations on the server side and to network latency. We took advantage of the fact that it is possible to directly predict the forces rather than having to predict the device position, as it is the case for most of the systems using prediction to deal with time delays. The predictive part thus relied on haptic values precomputed during the training session, and the corrective part used real haptic values and a third-order convergence mechanism. In the absence of a physical haptic interface specific to scoliosis surgery, to be developed in a future project, we used a color-coded visual rendering of haptic values and a pseudo-haptic rendering that modified the control / display ratio, i.e. the surgical tool movement visual restitution gain. We improved users' feeling of telepresence during training sessions by sharing haptic values and implant, rod, and manipulated tool changes in position among clients, and demonstrated through collaborative transatlantic and transcontinental tests that the simulator was functional in realistic conditions. The simulated force profile of a specific scoliotic case has been evaluated by a small group of expert surgeons with a simple mechanical apparatus recreating the rod rotation manoeuvre.