The Department of Computer Science at the University of Hull and the Orthopaedic Department of the Hull Royal Infirmary and Castle Hill Hospital are currently developing a Virtual Environment Knee Arthroscopy Training System (VEKATS) offering trainee surgeons an effective environment to acquire skills such as triangulation, orientation and dexterity, necessary to perform an arthroscopic procedure. VEKATS is trying to integrate the advantages of both video-disc based and computer graphics based surgical simulators in order to serve diagnostic as well as operative purposes. Deformable objects are introduced permitting the trainee to interact in real-time with soft tissue. At present, the research team is working on a prototype force feedback device allowing the student to get a feel for the hardness of the bone and the flexibility of the soft tissues.
Endoscopic training in a controlled setting, outside the operating theatre, outperforms the traditional methods using physical replica anatomy models which rapidly degrade through wear and tear. Moreover, the virtual environment surgery simulator enables research on pathology cases and can easily be enhanced with annotations and multimedia tutorials. At the moment, two types of simulator exist: those which play real endoscopic images stored on a video disc and those which generate anatomical imagery through computer graphics animations. The former offer an impression of smooth motion since the image retrieval is sufficient to produce a relatively high frame-rate. However, surgical training is difficult because the system provides only prerecorded real anatomical images.
There are two categories of computer graphics based surgical simulators, namely systems for diagnostic visualisation of MRI and CT scans and systems for the training of endoscopic techniques. The surgical simulator ideally has to respond to a set of criteria which basically include smooth visual feedback, accurate depiction of anatomy, force feedback, high interactivity and deformable tissues. Simulators actually in use or in development all share the recurring problem of slow rendering rates resulting in a numerical instability which may distract the user. Researchers therefore are striving to achieve a compromise between detailed scenes and smooth rendering rates.
The VEKATS project is aiming to reconcile the best of both worlds. The system comprises a "virtual" geometrical model of the knee, presenting an arthroscope view and an anatomical overview. A video window is provided in which excerpts of real arthroscopic procedures can be replayed. A control panel permits to supervise the simulation. Trainees interact with the system via an electromagnetic tracker input device that will be equipped with a suitable force feedback device in the future. The object modeller is the key component allowing detection of collision with objects, bulk movement of objects and deformation of soft tissues. Deformation is calculated by the Finite Element Method (FEM) which guarantees accurate and stable but still time-consuming results.
The VEKATS system disposes of a wide range of pathologies and will still extend to the modelling of unusual anatomical features for inclusion into the virtual knee. There are also plans to redesign the control panel into a fully-integrated multimedia tutorial package and to develop an objective scoring system evaluating the recorded skill area of each trainee to produce an individual targeted training plan. Last but not least, the force feedback system is constantly being refined. The current system is managed by a specially designed controller, while the force calculations and control process are carried out by the host computer. The introduction of a small amount of viscous damping during hard surface contact has improved the stability. Measurement of forces by a modified surgical instrument fitted with a force/torque sensor combined with video footage from the arthroscope will provide a record of the experienced forces as well as of the physical behaviour seen during typical procedures.
The VEKATS experience proves the necessary fusion of several research areas such as computer graphics rendering, video-image display, force feedback and physically-based modelling techniques. For more information on this issue, we refer to the University of Hull web site.