GS RUTHENBECK¹, AS CARNEY¹,², S TAN², KJ REYNOLDS¹
¹Flinders University of South Australia. ²Flinders Medical Centre, Adelaide, Australia.
It is recognised that even experienced surgeons demonstrate a learning curve when attempting new procedures1. Due to recent advances in computer graphics and force-feedback (haptic) technology, it is now possible to simulate a wide range of surgical scenarios so that patients do not suffer complications as a result of a surgeon's learning curve. Simulators have numerous benefits including the ability to simulate atypical anatomy and tasks the surgeon could reasonably expect to encounter on an infrequent basis. Surgical simulators in ENT are not entirely new and temporal bone and sinus surgery simulators are currently being used in clinical practice2. However, the combined use of virtual simulation and haptic technology has not previously been used to simulate tonsil surgery.
Subtotal tonsillectomy or intracapsular "tonsillotomy" is increasingly being used as a safer and less morbid intervention for sleep disordered breathing due to adenotonsillar hyperplasia3. Several studies have now shown its benefits over traditional tonsillectomy in terms of reducing postoperative pain and a faster return to normal diet4. The technique is completely different to that of traditional dissection tonsillectomy and few surgeons have experience in the technique. The technique is dependent on a surgeon removing most of the tonsil tissue but being aware of the approaching capsule, by a combination of identifying the slower dissection speed and recognition of the firmer tissue. If the capsule is breached, then muscle is exposed with increased post-operative pain and bleeding risk. The benefits of the subtotal approach are then negated. Hence, a haptic simulator would be ideal to train both specialist and junior surgeons in this new technique.
To create a physically and visually interactive simulation to help teach and practice subtotal tonsillectomy.
Realistic 3-dimensional models were prepared of a patient (Fig. 1). Detailed textures and realistic shading techniques were used to give the simulated patient a realistic appearance. Detailed models of the mouth, teeth, and throat were added and animated into a pose similar to that commonly encountered in theatre.
Particular attention was given to accurately simulating surgical interactions. A new method of tissue simulation, recently developed in-house, was used to provide accurate tactile feedback. The tissue simulation5 (Fig. 2) realistically models the behaviour of the tissue in response to user interactions. This is achieved using specialized algorithms that leverage recent advances in the parallel computing power of graphics processing units (GPUs) to perform a physically-based simulation of tissue dynamics in real-time. The simulated tissue can be interactively manipulated, cut and ablated.
Precise force-feedback was delivered via a haptic control device (Fig. 3 [left]) with a replica Coblation handpiece (Fig. 3 [right]).
Regular feedback from surgeons was used during development to ensure an accurate haptic experience was achieved. Current limitations include the absence of bleeding and the shape of the tissue which will benefit from further refinement to more accurately represent tonsil anatomy. These limitations should be easily correctable with further development. The surgeon receives accurate force feedback as tissue is palpated or removed. This allows a surgeon to recognise when the capsule has been breached. Fig. 1 and Fig. 4 show screen captures of the current version of the simulator.
We have successfully produced a prototype virtual reality haptic simulator for subtotal tonsillectomy. The simulator provides a risk free environment for surgeons to practice subtotal tonsillectomy using the Coblation handpiece. Early feedback suggests that tactile feedback improves learning and thereby reduces the learning curve normally encountered during development of expert proficiency. Other ENT techniques could also be taught using this computer methodology.
1. A.S. Carney, P.K. Harris, P.L. McFarlane, S. Nasser, A. Esterman (2008) The coblation tonsillectomy learning curve. Otolaryngology-Head and Neck Surgery, 138: 149-152
2. K-e.A. Abou-Elhamd, A.I. Al-Sultan, U.M. Rashad (2010) Simulation in ENT medical education. The Journal of Laryngology & Otology, 124: 237-241
3. E. Hultcrantz, A. Linder, A. Markstrom (2005) Long-term effects of intracapsular partial tonsillectomy (tonsillotomy) compared with full tonsillectomy. International Journal of Pediatric
Otorhinolaryngology, 69: 463-469.
4. P.J. Koltai, C.A. Solares, J.A. Koempel, K. Hirose, T.I. Abelson, P.R. Krakovitz, J. Chan, M. Xu, E.J. Mascha (2003) Intracapsular tonsillar reduction (partial tonsillectomy): Reviving a historical procedure for obstructive sleep disordered breathing in children. Otolaryngology-Head and Neck Surgery, 129: 532-538
5. G.S. Ruthenbeck (2010) Interactive Soft Tissue for Surgical Simulation. PhD Thesis. Flinders University of South Australia.