Discussion

When it comes to surgical education, objective practices must be adopted to improve operative technique and patient safety.^{Reference Agha and Fowler15} In this study, it was shown that the use of synthetic materials allowed us to achieve these goals and ensure reproducibility through the use of readily accessible and affordable supplies, provided that the necessary surgical instruments and magnifying optics are available. In simulation settings, synthetic material, albeit less tactile, elastic and compliant than organic tissue, enables repetitive use because of its characteristic low cost. Furthermore, it eliminates the risk of contamination, ethical conflicts and difficulty of acquisition.^{Reference Tan and Sarker16}

The cost of model fabrication was low and could be made even lower if the service had a 3D printer and a qualified designer on its staff, which would reduce expenditures to the cost of the filament, paint and magnets used. The cost of the simulator is thus limited to the cost of printing and finishing. On comparison with simulators used in other areas of otolaryngology, as reported in a systematic review,^{Reference Nogueira Júnior and Cruz4} the production cost of this model is compatible with its fabrication at scale. Compared with existing models of the same procedure,^{Reference Sparks, Kavanagh, Vargas and Valdez17} the 3D-printed simulator presented here is less expensive and offers the possibility for local production, showing that high-cost devices are unnecessary to achieving an educational objective. Chan et al.^{Reference Chan, Carrillo and Ong18} also published a low-cost model assembled from pre-existing materials. Therefore, simulators for this procedure can be designed to be affordable to interested institutions and reproducible across different otolaryngology teaching environments. There are several examples in the literature of authors pursuing such goals, including in otological surgery.^{Reference Barber, Kozin, Dedmon, Lin, Lee and Sinha9,Reference Sparks, Kavanagh, Vargas and Valdez17,Reference Ganguli, Pagan-Diaz, Grant, Cvetkovic, Bramlet and Vozenilek19,Reference Vaitaitis, Dunham, Kwon, Mayer, Evans and Baker20} As of 27 July 2020, the Brazilian real exchange rate was approximately R$5.55 to the dollar (US$ 1.00 = R$0.18); the total cost of the project was therefore US$88.99.

Anschuetz et al. reported better adaptation to use of the endoscope as opposed to the microscope by otologic surgeons, especially in students and residents with little experience in the field.^{Reference Anschuetz, Stricker, Yacoub, Wimmer, Caversaccio and Huwendiek21} In cadaver training, endoscopy was the method that best avoided accidents, in addition to providing the advantage of wide visualisation in a restricted space.

Nevertheless, both endoscopic and microscopic surgery could be reproduced in the model (Figure 3), although ease of manipulation was greatest with the microscope because there was no technical difficulty due to an excess of instruments in the restricted space of the external auditory canal. Barber et al. ^{Reference Barber, Kozin, Dedmon, Lin, Lee and Sinha9} designed a polylactic acid model for simulation of endoscopic ear surgery in order to improve dominant and non-dominant hand performance through simple transcanal activity; they also noted the difficulty of operating through an endoscope in an inflexible cavity and the challenge inherent to endoscopic surgical technique of being single-handed.

Otological surgery techniques are essentially dependent on operator experience and on the armamentarium available at each service, as evaluated in a comparative pilot study specifically regarding insertion of ventilation tube.^{Reference Martellucci, Pagliuca, de Vincentiis, De Virgilio, Fusconi and Gallipoli22} Therefore, apprentice surgeons have the possibility of acquiring two distinct techniques, depending on how well they adapt to each. It also bears stressing that it is important to invest in the more recent modality of endoscopic ear surgery, as its popularity is on the rise and it allows better visualisation of structures than the operating microscope, which is limited by lighting and angulation constraints.^{Reference Cohen, Landegger, Kozin and Lee23} The model proposed in this article allows training in both modalities.

Another advantage of the model is its portability. Its reduced dimensions mean it is easily transported, as are previous models reported in the literature,^{Reference Sparks, Kavanagh, Vargas and Valdez17,Reference Vaitaitis, Dunham, Kwon, Mayer, Evans and Baker20,Reference Anschuetz, Stricker, Yacoub, Wimmer, Caversaccio and Huwendiek21} and may even allow its later sale and wide distribution.

As for the tympanic membrane simulation, the authors were satisfied with the attributes of a clear plastic bag, which is readily acquired anywhere at little to no cost and can be used countless times. Sparks et al. used tympanic membranes made from rubber at a cost of a few cents of a dollar each; however, these still had to be made to order.^{Reference Sparks, Kavanagh, Vargas and Valdez17}

The use of magnets at the interface between the base and detachable portions of the simulator provided some degree of seal. However, considering that the presence of fluid effusion in the middle ear is common in diseases which indicate tympanostomy, an improved watertight design would be required to simulate this; infusion of water into our simulator caused rapid extravasation. We are planning a new version of the design with this capability, in addition to the possibility of increasing volume in the tympanic cavity, to better simulate the volume of effusion aspirated during the procedure and to avoid leakage during model assembly. In another study, the authors assembled their model from individually printed parts which join together and allow simulation of surgery under the operating microscope.^{Reference Vaitaitis, Dunham, Kwon, Mayer, Evans and Baker20}

Future research might test improvements of the model described herein, which would allow its use for simulation of other invasive techniques, such as transtympanic injection of medication and type I (inlay) tympanoplasty with tragus cartilage graft, for example. Adjustments will be planned for a new and enhanced version of the simulator.

As for the limitations of the model, its light weight was found to cause some difficulty during manipulation, as it was easily displaced during both endoscopy and microscopy, increasing training time during tests performed by the authors.

Additionally, dealing with synthetic materials reduces the technical difficulty inherent to the anatomy and physiology of each individual ear. Such materials do not simulate complicating elements such as bleeding, tortuous or stenotic external auditory canals, manipulation of the ossicular chain, facial nerve canal dehiscence, or adhesive otitis, among others.^{Reference Ragab, Mohammed, Abdel-Fattah and Afifi24} These are not necessarily disadvantages, but the resulting ease of the simulated procedure is beyond the realm of probability in human patients. Therefore, the aim of the simulator is to provide the surgeon-in-training with the ability to handle instruments in restricted surgical fields, such as the external auditory canal and the tympanic cavity, improving fine motor dexterity in a near-optimal setting before applying these skills to real cases.

It is also worth noting that this is the only description of a model capable of simulating myringotomy and tympanostomy both by microscopy and by endoscopy. The proposed model fulfilled the authors’ expectations and criteria as a safe, inexpensive, reproducible, user-friendly and accessible surgical education tool, which can be improved and reassessed for further research.