Virtual reality simulator: demonstrated use in neurosurgical oncology.

BACKGROUND: The overriding importance of patient safety, the complexity of surgical techniques, and the challenges associated with teaching surgical trainees in the operating room are all factors driving the need for innovative surgical simulation technologies. TECHNICAL DEVELOPMENT: Despite these issues, widespread use of virtual reality simulation technology in surgery has not been fully implemented, largely because of the technical complexities in developing clinically relevant and useful models. This article describes the successful use of the NeuroTouch neurosurgical simulator in the resection of a left frontal meningioma. CONCLUSION: The widespread application of surgical simulation technology has the potential to decrease surgical risk, improve operating room efficiency, and fundamentally change surgical training.

Fundamentals of neurosurgery: virtual reality tasks for training and evaluation of technical skills.

BACKGROUND: Technical skills training in neurosurgery is mostly done in the operating room. New educational paradigms are encouraging the development of novel training methods for surgical skills. Simulation could answer some of these needs. This article presents the development of a conceptual training framework for use on a virtual reality neurosurgical simulator. METHODS: Appropriate tasks were identified by reviewing neurosurgical oncology curricula requirements and performing cognitive task analyses of basic techniques and representative surgeries. The tasks were then elaborated into training modules by including learning objectives, instructions, levels of difficulty, and performance metrics. Surveys and interviews were iteratively conducted with subject matter experts to delimitate, review, discuss, and approve each of the development stages. RESULTS: Five tasks were selected as representative of basic and advanced neurosurgical skill. These tasks were: 1) ventriculostomy, 2) endoscopic nasal navigation, 3) tumor debulking, 4) hemostasis, and 5) microdissection. The complete training modules were structured into easy, intermediate, and advanced settings. Performance metrics were also integrated to provide feedback on outcome, efficiency, and errors. The subject matter experts deemed the proposed modules as pertinent and useful for neurosurgical skills training. CONCLUSIONS: The conceptual framework presented here, the Fundamentals of Neurosurgery, represents a first attempt to develop standardized training modules for technical skills acquisition in neurosurgical oncology. The National Research Council Canada is currently developing NeuroTouch, a virtual reality simulator for cranial microneurosurgery. The simulator presently includes the five Fundamentals of Neurosurgery modules at varying stages of completion. A first pilot study has shown that neurosurgical residents obtained higher performance scores on the simulator than medical students. Further work will validate its components and use in a training curriculum.

A literature review of the numerical analysis of abdominal aortic aneurysms treated with endovascular stent grafts.

The purpose of this paper is to present the basic principles and relevant advances in the computational modeling of abdominal aortic aneurysms and endovascular aneurysm repair, providing the community with up-to-date state of the art in terms of numerical analysis and biomechanics. Frameworks describing the mechanical behavior of the aortic wall already exist. However, intraluminal thrombus nonhomogeneous structure and porosity still need to be well characterized. Also, although the morphology and mechanical properties of calcifications have been investigated, their effects on wall stresses remain controversial. Computational fluid dynamics usually assumes a rigid artery wall, whereas fluid-structure interaction accounts for artery compliance but is still challenging since arteries and blood have similar densities. We discuss alternatives to fluid-structure interaction based on dynamic medical images that address patient-specific hemodynamics and geometries. We describe initial stresses, elastic boundary conditions, and statistical strength for rupture risk assessment. Special emphasis is accorded to workflow development, from the conversion of medical images into finite element models, to the simulation of catheter-aorta interactions and stent-graft deployment. Our purpose is also to elaborate the key ingredients leading to virtual stenting and endovascular repair planning that could improve the procedure and stent-grafts.

NeuroTouch: a physics-based virtual simulator for cranial microneurosurgery training.

BACKGROUND: A virtual reality neurosurgery simulator with haptic feedback may help in the training and assessment of technical skills requiring the use of tactile and visual cues. OBJECTIVE: To develop a simulator for craniotomy-based procedures with haptic and graphics feedback for implementation by universities and hospitals in the neurosurgery training curriculum. METHODS: NeuroTouch was developed by a team of more than 50 experts from the National Research Council Canada in collaboration with surgeons from more than 20 teaching hospitals across Canada. Its main components are a stereovision system, bimanual haptic tool manipulators, and a high-end computer. The simulation software engine runs 3 processes for computing graphics, haptics, and mechanics. Training tasks were built from magnetic resonance imaging scans of patients with brain tumors. RESULTS: Two training tasks were implemented for practicing skills with 3 different surgical tools. In the tumor-debulking task, the objective is complete tumor removal without removing normal tissue, using the regular surgical aspirator (suction) and the ultrasonic aspirator. The objective of the tumor cauterization task is to remove a vascularized tumor with an aspirator while controlling blood loss using bipolar electrocautery. CONCLUSION: NeuroTouch prototypes have been set up in 7 teaching hospitals across Canada, to be used for beta testing and validation and evaluated for integration in a neurosurgery training curriculum.

Modeling the thermal effect of the bipolar electrocautery for neurosurgery simulation.

Real-time surgical simulation requires computationally-fast models describing the interaction between surgical instrument and tissues. In this study, a model for predicting the temperature distribution in brain tissue when using a bipolar electrocautery is proposed and validated against experimental in vitro animal data. Joule heat generation and heat conduction in the tissue are considered. The agreement between simulated temperature distributions and experimental data could be improved by modeling the output power as a function of electrical resistance between the electrodes, and by considering the heat exchange with surrounding air and bipolar tips.

A computer model of soft tissue interaction with a surgical aspirator.

Surgical aspirators are one of the most frequently used neurosurgical tools. Effective training on a neurosurgery simulator requires a visually and haptically realistic rendering of surgical aspiration. However, there is little published data on mechanical interaction between soft biological tissues and surgical aspirators. In this study an experimental setup for measuring tissue response is described and results on calf brain and a range of phantom materials are presented. Local graphical and haptic models are proposed. They are simple enough for real-time application, and closely match the observed tissue response. Tissue resection (cutting) with suction is simulated using a volume sculpting approach. A simulation of suction is presented as a demonstration of the effectiveness of the approach.

In-vivo validation of a stent implantation numerical model.

A large deformation finite element model for the patient-specific prediction of stent implantation is presented as a potential tool to assist clinicians. The intervention simulation includes the complete stent deployment under balloon inflation and deflation in the artery. This paper describes the proposed model and presents an in-vivo validation of the model using pre- and post-intervention data from a patient who underwent stent implantation. Predicted cross-section areas at different artery positions are compared to post-intervention measurements. This work demonstrated the model's potential to become a relevant tool for predicting the arterial response to the intervention.

Computer prediction of balloon angioplasty from artery imaging.

The success of angioplasty depends on a balance between two conflicting objectives: maximization of artery lumen patency and minimization of mechanical damage. A finite element model for the patient-specific prediction of angioplasty is proposed as a potential tool to assist clinicians. This paper describes the general methodology and the algorithm that computes device/artery friction work during balloon insertion and deployment. The potential of the model is demonstrated with examples that include artery model reconstruction and prediction of friction on the arterial wall during balloon insertion and deployment.

Kinematics of the ankle joint complex in snowboarding.

Because snowboarders are known to injure their ankles more often than Alpine skiers, it has been postulated that stiffer snowboard boots would provide better protection to the ankle than current soft boots do. Snowboarders are also known to injure their front ankle more often than their back ankle, presumably because of the asymmetrical rotations of the ankles due to asymmetrical binding adjustement. To test these hypotheses, we measured the kinematics of the feet and legs of 5 snowboarders wearing soft boots and stiffer step-in boots during snowboarding maneuvers using an electromagnetic motion tracking system. The results were expressed in anatomically relevant rotations of the ankle joint complex, namely dorsi-/plantar flexion, eversion/inversion, and internal/external rotation. The measured ankle rotations show differences in the movement patterns of the front and back legs. Step-in boots were shown to allow less dorsiflexion, eversion, and external rotation than softer boots, possibly explaining why they are associated with a lower rate of fractures of the talus than soft boots.

Biomechanical evaluation of the Boston brace system for the treatment of adolescent idiopathic scoliosis: relationship between strap tension and brace interface forces.

STUDY DESIGN: Prospective study to evaluate the association between strap tension and brace interface forces in the treatment of adolescent idiopathic scoliosis using the Boston brace system. OBJECTIVES: To determine the strap tension associated with optimal brace interface forces. SUMMARY OF BACKGROUND DATA: Trim lines, pad placement, and areas of relief for the brace are guided by radiographic studies. However, optimal adjustment of strap tension is unclear and remains mostly empirical. METHODS: Brace interface forces in all regions of the trunk were measured for 41 patients with adolescent idiopathic scoliosis at three standardized strap tensions (20 N, 40 N, and 60 N). The brace interface forces were assessed using a mat made of force-sensing transducers. Equivalent interface pressure for each trunk region was also calculated to estimate the distribution of the interface forces. RESULTS: The brace interface forces and the corresponding effective areas increased along with the strap tension for all patients. For patients with a single right thoracic curve, the interface pressure tended to increase with increasing strap tension. This increase was significant in the left axillary, right thoracic, right pelvic, and sternal regions. For double right thoracic-left lumbar curves, the increase in interface pressure was significant in the left axillary, right pelvic, and sternal regions. However, most of this increase occurred between 20 N and 40 N of strap tension, with only slight increase or even a decrease in interface pressures between 40 N and 60 N. CONCLUSIONS: The strap tension should be set as high as possible (up to 60 N) for right thoracic curves. For right thoracic-left lumbar curves, the optimal strap tension was approximately 40 N. However, clinicians should ensure that the prescribed strap tension does not cause excessive skin pressure or affect the compliance with the brace. A side opening in the right lumbar area may improve the effectiveness of the brace for double right thoracic-left lumbar curves, but care must be taken to avoid skin problems at the opening.

Is Cobb angle progression a good indicator in adolescent idiopathic scoliosis?

STUDY DESIGN: A retrospective follow-up study of spine geometry after posterior instrumentation and fusion for adolescent idiopathic scoliosis (AIS). OBJECTIVES: To evaluate 1) if Cobb angle progression is a reliable indicator of the crankshaft phenomenon; 2) if significant growth of the spine can occur after surgery without the development of a crankshaft phenomenon? SUMMARY OF BACKGROUND DATA: Anterior fusion of the spine is often recommended for skeletally immature scoliotic patients to avoid the risk of a crankshaft phenomenon, a long-term loss of curve correction caused by residual growth of the spine combined with the constraints of a posterior fusion. The crankshaft phenomenon is usually assessed indirectly by documenting progression of the Cobb angle on frontal radiographs. Thus far, no study has directly measured the three-dimensional growth of the spine after surgery in AIS. METHODS: Cobb angle, spine length and spine height were obtained from three-dimensional radiographic reconstructions of the spine in 48 adolescent scoliotic patients undergoing posterior instrumentation and fusion. Measurements were done before surgery, after surgery and at skeletal maturity. A significant growth of the spine was defined as a > or = 10 mm increase in spine length, while a significant curve progression was defined as a > or = 10 degrees increase in Cobb angle at skeletal maturity. RESULTS: In the majority of patients (56%), there was no significant change in spinal length or in Cobb angle measurements at an average 2.4 years post surgery. A crankshaft phenomenon was detected in 6 patients (12%) for which significant increases both in spinal length and Cobb angle measurement were found. Significant curve progression without any change in spine length was noted in 9 patients (19%) while an increase in spine length with no evidence of curve progression was present in 6 patients at last follow-up. CONCLUSION: Spinal growth as indicated by an increase in spinal length can be measured in a significant proportion of adolescents with idiopathic scoliosis after posterior instrumentation and fusion. Some of these study participants will develop a crankshaft phenomenon but Cobb angle progression is not a reliable indicator of this complication, since it may occur without any detectable growth of the spine.