Recent advances in computing and haptic devices now allow the pressure and temperature sensory receptors in human skin to be cheated. In order to create the sensation of touching and manipulating virtual objects in real time, we need to generate the reaction force over them. These receptors are spread over a large area and are extremely fast, so the reflecting force must be recalculated over 1000 times per second. This is a complex challenge when we deal with deformable bodies as in MIS.
MIS techniques offer important advantages, such as decreasing patient trauma and reducing costs, but they also have an important drawback: they are complex procedures and difficult to master. Traditional learning methods, assuming the importance of force feedback, use real surgical instruments with phantoms (plastic models) for training. However this set of instruments is expensive and delicate; moreover, the plastic models degrade due to the incisions until they become unusable.
Here virtual reality and haptics have come up with the solution. Our team, in cooperation with the company GMV, is developing a successful advanced arthroscopy training simulator, based on virtual reality. Using this simulator, the practitioner learns to handle the surgical instruments and to recognize pathologies. The incorporation of a haptic device facilitates triangulation and navigation learning, making it possible to feel and distinguish between different tissues.
Current haptic MIS training systems can be classified as either general purpose devices (eg from SensAble PHANToM) or brand new devices dedicated to surgical simulation (eg Immersions Laparoscopy Impulse Engine, Virtual Laparoscopic Interface-VLI without force-feedback, and Laparoscopic Surgical Workstation with force-feedback). We have designed a dedicated system, but there remain some limitations that we want to solve.
Shoulder arthroscopy requires a very flexible working area, especially regarding inter-trocar distance (this is fixed in current devices at 135mm). Human body dimensions differ from one patient to another, and this technique necessitates the simultaneous positioning of each trocar on every side of the patients shoulder.
We need both surgical instruments to face on, one trocar against the other: this is not normally possible because of the main stand structure. It is therefore necessary to include this additional degree of freedom.
It is crucial to ensure that even if the instruments face each other, and the minimum lateral distance between them has been established, they do not touch one another.
The suggested design, the Laparoscopy Training System, provides the usual five degrees of freedom (including a scissors handle option in order to simulate grasping forces), plus two additional degrees. These are a lateral displacement of every actuator set (adaptive inter-trocar distance) and a rotation of these sets around the device symmetry axis. Moreover, the design allows an ergonomic positioning of the surgical instruments depending on the preference of the trainee.
Our work is focused on designing an MIS training system to simulate specific laparoscopy techniques that are not generally considered. Having finished the design stage, a prototype is under construction, and a working device should be achieved by summer 2005.
Nowadays, the features of physical devices restrict programmers due to limitations in the number of degrees of freedom. We think that this design will help to solve these constraints
José San Martín, Universidad Rey Juan Carlos/SpaRCIM, Spain