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The Role of Mixed Reality Simulation for Surgical Training in Spine: Phase 1 Validation

Coelho, Giselle, MD; Defino, Helton L.A., PhD, MD

doi: 10.1097/BRS.0000000000002856

Study Design. This study shows the first phase of validation of a new model for realistic training on spine surgery, conducted from January 2014 to November 2015.

Objective. To propose and validate a new tool for neurosurgical education, associating virtual and realistic simulation (mixed reality), for spine surgery.

Summary of Background Data. Surgical simulation is a relatively new filed that has a lot to offer to neurosurgical education. Training a new surgeon may take years of hands-on procedures, increasing the risk to patient's safety. The development of surgical simulation platforms is therefore essential to reducing the risk of potentially serious risks and improving outcome.

Methods. Sixteen experienced spinal surgeons evaluated these simulators and answered the questionnaire regarding the simulation as a beneficial education tool. They evaluated the simulators in regard to dissection by planes, identification of pathology (lumbar canal stenosis), instrumentation and simulation of cerebrospinal fluid (CSF) leak, and the relevant aspects of the computerized tomography (CT) imaging.

Results. The virtual and physical simulators for spine surgery were approved by an expert surgery team, and considered adequate for educational purposes. The proportion of the answers was estimated by the confidence intervals.

Conclusion. The surgery team considered that this virtual simulation provides a highly effective training environment, and it significantly enhances teaching of surgical anatomy and operative strategies in the neurosurgical field. A mixture of physical and virtual simulation provided the desired results of enhancing the requisite psychomotor and cognitive skills, previously acquired only during a surgical apprenticeship. The combination of these tools may potentially improve and abbreviate the learning curve for trainees, in a safe environment.

Level of Evidence: 3

Pediatric Neurosurgery Center/CENEPE – Beneficência Portuguesa Hospital, São Paulo, Brazil.

Address correspondence and reprint requests to Giselle Coelho, MD, Pediatric Neurosurgery Center / CENEPE – Beneficência Portuguesa Hospital, São Paulo, Brazil; E-mail:

Received 14 September, 2016

Revised 17 November, 2016

Accepted 14 December, 2016

The manuscript submitted does not contain information about medical device(s)/drug(s).

The SIEDI Research Institute funds were received in support of this work.

No relevant financial activities outside the submitted work.

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Website (

Back pain comprises an array of nonspecific complaints, being usually the beginning of a benign process, yet causing concern of a more serious disease, and overimaging can lead to no identifiable pathology.1,2 In order to increase patient safety and improve treatment outcomes, several strategies as problem-based learning and objective structured clinical examination have promoted the development of new curricula in surgical education.3–7 Furthermore, objective measures of surgical competence are needed to offset the tendency towards bias in skill assessing.8,9 The necessity of innovative surgical curriculum development that incorporates safe learning environments and objective skills assessments is thus obvious, and needs to be led by trained surgical educators.10,11

Since the Flexner Report in 1910,12 there has been a revolution in medical education, reaching every level of education, and even one that is driven by new methodologies and innovative technologies. Although all other industries (aviation, mining, military, textile) have already been using virtual design simulation for prototyping and evaluation, training and assessment, simulation has been made available to medical education only in the past decade. Yet, its impact has been truly profound.13 One of the most important benefits of simulation is that it gives “permission to fail” in a safe environment, and students can learn from their mistakes.

A Yale University study demonstrated that criterion-based simulator training decreased operating time by 30% and operative errors by 85%.10,14 Surgical simulation, in this context, can help address shortcomings in the traditional apprenticeship-training model by providing residents with opportunities to practice important procedures that they may not otherwise encounter and practice efficiently until competency is achieved, and mainly without exposing patients’ lives to undue risk.15 Also, we emphasize that the learning process is not only technical, it requires theoretical knowledge and training.

There are reports of simulators to intracranial and spinal neurosurgical procedures,16,17 both human and animals.18,19 Thus the main goal of this study was to propose a new tool for Neurosurgical Education that combines virtual and realistic simulation (mixed reality) in order to create an authentic surgical safe training environment for spine surgery that can be ethically and financially adequate, that is complementary to the options available today.

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This study shows the first phase of validation of a new model for realistic training on spine surgery, conducted from January 2014 to November 2015. Sixteen experienced spinal surgeons evaluated these simulators and answered the questionnaire regarding the simulation as a beneficial education tool (SDC questionnaire, They evaluated the simulators in regard to dissection by planes, identification of pathology (lumbar canal stenosis), instrumentation and simulation of cerebrospinal fluid (CSF) leak, and the relevant aspects of the computerized tomography (CT) imaging.

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Spine Physical Simulator

The physical simulator, developed by Brazilian company ProDelphus, was made with a synthetic thermo-retractile and thermo-sensible rubber which, when combined with different polymers, produces more than 30 different formulas. These formulas present textures, consistencies, and mechanical resistance similar to many human tissues. It was possible to perform computerized tomography images for all simulators due to the radio-opacity and to compare the pre and postoperative images.

The spine realistic simulator is composed of: a lumbar area with skin, subcutaneous and muscular tissues, ligaments, lumbosacral vertebrae, spinal cord, CSF, and nerve roots (Figure 1). Some tests were made with different materials in order to achieve optimal spinal consistency to perform the instrumentation. The porcine vertebral model was also tested to try to obtain adequate haptic feedback during the surgical procedure.20 The presence of the spinal cord and dura mater, filled with saline solution to represent the CSF, allows the simulation of some realistic intraoperative challenges, such as CSF leak, making it possible to solve the problem. It was possible to obtain CT imaging, consequently allowing the comparison between the pre and postoperative images (Figure 2A–D).

Figure 1

Figure 1

Figure 2

Figure 2

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Spine Virtual Simulator

The spine virtual simulator comprises the representation of lumbar stenosis and its surgical approach at 2 levels (L2–L3 and L3–L4), and allows exploration from different angles. The modules available in the spine trainer were: patient position, skin incision, pedicle screw placement, lumbar decompression, and spinal instrumentation (Figure 3A–E). The simulator is able to perform the following techniques: nerve root decompression, spine instrumentation, microdiscetomy, and surgical complication CSF fistulae.

Figure 3

Figure 3

The main goal was to prove that the virtual simulations could provide the realistic training with a physical platform. Although these virtual models are limited in regard to their real-time interactions with the trainee, their goal is to stimulate the ability to mentally manipulate objects in three dimensions, recreating the intraoperative scenario, essential to the practice of these operations. All of them were built with real surgical procedures (surgeon expertise and pictures) and correspondence of the physical simulators to the relevant pathological findings.

Sixteen experienced spinal surgeons (both spine surgeons and orthopedic surgeons) evaluated these simulators and answered the questionnaire regarding the simulation as a beneficial education tool. They evaluated the simulators in regard to dissection by planes, identification of pathology (lumbar canal stenosis), instrumentation and simulation of CSF leak, and the relevant aspects of the CT imaging.

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Sample Size Calculation

Sample size calculation was performed to support the number of surgeons in the study. In São Paulo there are around 300 full professors in spine surgery. From these 300 surgeons, approximately 30% are renowned in the international literature. For this reason, we used a range of 10% to 20% of the surgeons. The standard deviation for the difference between the scores was 20% (calculated from population control), with a confidence interval of 95% and 80% power, the number of participants to detect a measurable sensitivity, was calculated in 16 surgeons. Assuming a loss rate and waiver of 10%. The study was considered complete when 16 doctors joined the research.

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Questionnaire Sensitivity

Cronbach α is a method used to check the internal consistency of the data. This method has been widely used to estimate the reliability of measuring instruments. Before beginning the results we defined a standard error of 5%. The internal consistency of the questionnaire of 23 questions was calculated at α = 0.45. Two ratio equality tests were applied to characterize the distribution of relative frequencies (percentages) of all questions.

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Clinical and Anatomical Evaluations Questionnaire

The following aspects were evaluated: consistency, resistance, tactile identification, applicability of the simulator for training novice surgeons, and an overall score of realistic simulation capacity (Supplemental digital content (SDC) Tables 1, 2, and 3,, for the procedures described above. Consistency was defined as the degree of density or firmness of the material that the simulator exhibited. Resistance was defined as the behavior of simulator structures to procedural stresses and strains. To be considered adequate for a procedure, the simulator must be able to reproduce similar anatomy and surgical techniques as those required in the equivalent real procedure.

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Statistical Analysis

Cronbach α was used to verify the internal consistency of the questionnaire consisted of 23 questions. The two-proportion equality test (Chi-square) was used as a means of comparing the proportion of answers for two specific variables. Data are presented as absolute and percentage. Differences were considered significant at P < 0.05.

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Questionnaire Validation

All the aforementioned simulators (virtual and physical) were submitted to a scientific validation process. This consisted of a questionnaire presented to the expert surgeons after their interaction with the simulators (SDC). The formulated questions covered several aspects of the experience. For instance, in the virtual model, the evaluation addressed the geometric and the anatomical representation, the multiangular view, and if and how it could improve the neurosurgical resident understanding. Regarding the physical models, questions about consistency and resistance of the tissue, size, anatomical correspondence to the real patient and radiological interface were emphasized. The results shown in Figure 4 below regarding the answers given by the physicians, and were estimated by the confidence intervals. At the end of the assessment, an index was created to summarize all the answers: the general score of realistic simulation, with a Cronbach α value of 0.845.

Figure 4

Figure 4

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Spine Realistic Simulator

The physical simulators allowed the practice of pedicle screw placement and lumbar stenosis decompression surgery. Many components of the procedures could be practiced using this simulator such as: the skin incision; the subcutaneous, muscular and subperiostal dissection; the laminectomy and placement of the pedicle screws. The presence of the spinal cord and dura mater, filled with saline solution representing CSF, allowed the simulation of intraoperative challenges such as CSF leak (Figures 5 and 6A, B).

Figure 5

Figure 5

Figure 6

Figure 6

Regarding material resistance, 56.25% of the surgeons considered that the anatomical structures of the simulator were different from normal tissue with no effects to the surgical simulation, or considered the material similar to normal tissue, without the need to for structural alteration (Figure 4A and SDC Table 2, In terms of the comparative size and shape of the anatomical structures (SDC Tables 4–16,, the participants assessed the simulator to be adequate, with scores of 100% and 95% for these two aspects, respectively (Figure 4B and SDC Table 3, The majority of the participants (94%) felt that the simulator was able to provide a field for developing skills and/or alter the attitudes of trainee surgeons (Figure 4C). Radiologic evaluation demonstrated that the structural positioning, the anatomical scale, and the radio-opacity were unanimously considered appropriate (100%) (Figure 4D). Finally, an overall score for realistic simulation was created, as illustrated in Figure 7. Thereby, it was observed that 11 of the experienced surgeons (68.75%) judged the spine simulators to be useful for practical application with trainees (Figure 4E).

Figure 7

Figure 7

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Spine Virtual Simulator

Regarding the spine virtual simulator, the following items were evaluated: patient positioning; dissection by planes, spinal instrumentation, lumbar decompression; multiangular observation, and tridimensional representation. Fifteen experts (93.75%) considered the 3D reconstruction adequate and the 3D material was endorsed for presentation to spine surgery trainees (SDC Tables 17 and 18,

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Many models have been created as an initial step in training residents and young spine surgeons to gain experience with surgical procedures. The majority of these have used animal models, human cadaveric specimens, or even synthetic materials.21–26

Cadaveric dissection is still considered the gold standard for non-clinical surgical training, but it does not accurately replicate fine operative manipulations and it does not provide operating during specific pathologies. Moreover, it can have ethical implications in some countries and restrictions in its use for obtaining CT and scan. Cadaver acquisition and maintenance are also expensive and available only at major centers.27

Cadaveric brains have small ventricles, being difficult to cannulate and rendering ventriculostomy extremely difficult and not representative of the actual circumstances of the procedure. Some advance has been accomplished in an adult cadaver with induced ventricular dilatation.28 The same cadaveric anatomical restrictions can be cited for spine and craniosynostosis training. Animal models are also limited because of the ethical issues, problems with anesthesia, lack of reproducibility, and formidable cost.

Realistic physical adult models have previously been used successfully with outstanding reality.21,27 Here we show the first validation phase for a spine realistic simulator and a virtual spine simulator previously described by our group.21 The use of imaging allows integration with neuronavigation systems, consequently associating another training modality, as demonstrated before by Coelho et al.29 Considering the spine simulator, the radiological interface can also permit the minimally invasive techniques training. These anatomical models are composed of nontoxic materials and are easy to use, avoiding the difficulties inherent to cadaver and animal models, and providing an alternative to their use.21

Moreover, these physical simulators present other advantages that need to be highlighted: (1) the material maintenance is convenient and there is no need for any kind of special preparation. It is easier to maintain when compared with animal models and does not require anesthesia; (2) the model expresses the appropriate spine size and the dimensions observed in real patients. Thereby, the identification of anatomical landmarks and, more importantly, the depth perception are feasible; (3) these virtual and physical simulators include all the necessary planning steps of the surgery, from positioning to skin closure. The user is also allowed the normal degree of freedom for the surgical instruments to accurately perform the complex approaches; (4) the presence of CSF circulation in the spine simulator permit the handling of emergency situations; (5) the ability to obtain realistic imaging studies provides knowledge of the pathological condition and its diagnosis, and allows pre- and postoperative comparison studies; (6) the reproducibility is important and possible for both virtual and realistic simulators. This parameter is important for both scientific studies and the learning of surgical skills. Lastly, there are no ethical restrictions to its use or the necessity of a specific place to work with these simulators.

On the other hand, it is important to emphasize some disadvantages of these simulators. Although the handmade and hand tuned process of developing such a simulator has the most preferable characteristics (to represent the tissue properties adequately and to express the anatomical structures with precise localization), it can be difficult and extremely time consuming to create.

Virtual reality simulation is a promising alternative to surgical rehearsal for assessing the technical feasibility and skill. However, such components as tissue deformation and haptic feedback are missing, and these are necessary to provide a realistic training platform. Furthermore, virtual simulators do not allow the use of real instruments and have very high cost.27

However, when combined with physical simulation the teaching potential of virtual simulation can be strengthened. Virtual reality acts as a complementary tool, allowing varying degrees of immersion and realism. It provides a notion of physical reality, offering symbolic, geometric, and dynamic information. Although the virtual simulation described does not provide the haptic feedback (once the surgical procedures can be visualized), this technology enables: the detailed anatomical relationship understanding, the multiangular vision (through tissues not directly viewed during real surgery), and the simulation of all surgical steps with rich tridimensional visualization.

Kahol et al 30 published a study that proves the effectiveness of virtual reality simulation in preoperative warm-ups. In all of these pioneering efforts the measure for success has not only been decreasing time while increasing precision in performance of the competencies, but also in reducing errors while conducting a procedure or process, thereby improving patient safety.

As shown by Filho et al 31 the number of technical errors can be significantly reduced after the sixth procedure performed. There is therefore valuable potential for this realistic model to train a resident to a high level of objectively measured skill before he or she is permitted to attempt the procedure on a patient.27

Surgical simulation can decrease the operating time and the numbers of errors, increase the efficiency, and should thereafter be able to decrease liability.13 Previous investigators have reported class I data that supports the ability of simulators to improve performance in the operating room (OR).32–34

This report represents not only the description of the simulation tool, combining virtual and physical training platforms, but also reinforces their promising prospects. It should be considerably useful to abbreviate the learning curve during the qualification of young surgeons while minimizing the consequences of technical errors. Future studies will address scientific validation using well-defined performance measures, possibly followed by integration of this new educational tool into the neurosurgical curriculum. We believe that this teaching method will soon have the ability to improve the learning curve for technical skills on a simulator rather than on a patient.

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Key Points

  • Physical and virtual simulators developed for spine surgery by ProDelphus.
  • Questionnaire developed for evaluation by experienced surgeons.
  • Simulators were approved by neurosurgeons for resident training.

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The authors thank Marcos Lyra; Jair Lyra; Georgina Barretto, and Josemi Fabricio da Silva for their attendance and notable dedication in developing the physical simulators, and Gustavo Zagatto for the virtual simulators creation; Maíra Coelho R. Caselato and Valéria Aires Cruz for their assistance in preparing the pictures. Finally, the authors thank the simulation center SIEDI for the financial support.

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education; neurosurgery; physical simulator; realistic; simulation; spine; surgeons; training; validation; virtual; virtual simulator

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