A Novel Low-Cost, Open-Source, Three-Dimensionally Printed Thyroplasty Simulator

Abstract

Objective:

Training of surgical procedures on awake patients, such as medialization thyroplasty, poses challenges to educators and trainees. Three-dimensionally-printed simulators provide opportunity to practice in low-stakes settings. We present the first 3D-printed thyroplasty simulator incorporating a cartilaginous framework, endolaryngeal soft tissue housed in a 3D-printed manikin with endoscopic visualization.

Methods:

Male and female laryngeal cartilages and endolarynx molds were 3D-printed from an existing open-source design. Cartilage models were made of heat-treated polylactic acid (HTPLA), a material chosen for its thermal stability allowing drilling. They were combined with molded silicone endolarynges modeling glottic insufficiency. Larynges were set in a 3D-printed head-and-neck manikin with an attached borescope for internal visualization similar to distal chip laryngoscopy. Eight laryngologists evaluated the simulator by drilling a thyroplasty window, inserting an implant for medialization, and rating the model using a modified Michigan Standard Simulation Experience Scale (1=strongly disagree, 5=strongly agree).

Results:

The model was well-rated in educational value (mean 4.7, SD 0.3), fidelity (mean 3.8, SD 0.2), and overall value (mean 4.8, SD 0.5). Qualitative assessment concluded the model was anatomically realistic and that HTPLA was a good approximation of the density and texture of thyroid cartilage. The materials for one larynx cost $4.09.

Conclusion:

This high-fidelity 3D-printed simulator demonstrates educational value for thyroplasty training. The low-cost, open-source design has broad implications for universal access of this simulator platform.

Introduction

Use of simulators in otolaryngology has increased tremendously in the 21^st century. This may be attributable to restrictions on resident work hours¹ and an emphasis on competence-based assessments for trainees,² placing more emphasis on the need for novel teaching modalities to accommodate changing training environments. Simulation has emerged as one such educational tool that allows for practice and repetition of procedural skills in a controlled, low-stakes environment.

Simulation is particularly valuable in laryngology, as its contemporary practice encompasses numerous procedures performed while patients are awake or under conscious sedation. A 2019 qualitative study demonstrated that surgical residents experience several challenges when learning how to perform procedures on awake patients, including hesitance towards asking questions and issues with whispering or nonverbal communication with their teacher,³ further underscoring the potential utility of simulators in training for such procedures. Medialization thyroplasty, a procedure indicated for glottic insufficiency, is typically done on conscious patients in the operating room so that adjustments in vocal quality can be assessed in real-time. There are several key steps of this surgery that must be emphasized during training, including proper placement of the medialization window in the thyroid cartilage and placement of a surgical implant (e.g. silastic or GORE-Tex) to medialize the affected vocal fold.

A few thyroplasty simulators have been recently described in the literature. Animal models, such as an ex vivo ovine model,⁴ have been shown to be good tools for thyroplasty simulation by providing appropriate haptic feedback and including realistic anatomic relationships with neighboring structures. Recently, a 3D-printed thyroid cartilage model was described and used to simulate the creation of a medialization window.⁵ While this is a valuable reproducible tool for practicing this crucial step, this model does not include soft tissue or endoscopic visualization, such as in real-world scenarios.

To date, no simulator has been both easily reproducible and included comprehensive laryngeal anatomy. Our goal was to improve on the existing body of thyroplasty simulators by creating the first 3D-printed thyroplasty simulator that incorporates cartilaginous framework, endolaryngeal soft tissue, and head-and-neck manikin with endoscopic visualization. Furthermore, we aimed to ensure this simulator is both low-cost and open-source to make it widely available as an educational tool.

Materials and Methods

The original design for all 3D-printed products were published by Lee, et al.⁶ and the step-by-step protocol for producing the models was taken from the accompanying Wikifactory webpage (https://wikifactory.com/@3dlaryngology/3d-larynx-surgery-trainer). All 3D-printing was done using an Ender-3 printer (Creality, Shenzhen, China), which cost $189.00 USD.

A 3D-printed laryngeal cartilage framework was printed using heat-treated polylactic acid (Protopasta, Vancouver, Washington, USA), a filament chosen for its previous validation as an affordable material with good haptic feedback in relation to bony tissue⁷ and its superior integrity under the heat of friction created by a surgical drill. Plastic injection molds and a head-and-neck manikin were printed using polylactic acid (HATCHBOX, Pomona, California, USA). The molds were used to form endolaryngeal structures with EcoFlex 00–20 silicone (SmoothOn, Macungie, Pennsylvania, USA).

The simulator was assembled by adhering the endolaryngeal insert within the laryngeal cartilage framework using a silicone-based adhesive (Figure 1). Adhesive was place solely along the edges of the soft endolarynx to ensure that there was still mobility of the vocal folds upon insertion of a prosthetic during medialization. We created two different sizes of larynges to represent basic differences in male and female anatomy, as sex affects the size and placement of the thyroplasty window.

Figure 1:

Combined rigid laryngeal cartilage framework and soft-tissue endolarynx

The assembled larynx was placed into the head-and-neck manikin (Figure 2A). A borescope (ILIHOME, Shenzhen Zhiyi Technology Co., Guangdong, China), which cost $79.99, was inserted through a tailored canal in the manikin to allow for endoscopic visualization during manipulation of the model (Figure 2B). An SR80/102L desktop dental lab drill with a micromotor handpiece (Saeshin Strong, Irvine, California, USA) and 3 mm cutting drill burrs (ORAPXI International, Tianjin, China) were used to simulate the experience of performing medialization thyroplasty. The costs of these tools were $160.00 USD and $18.99 USD, respectively. Furthermore, we used strips of 0.5 mm thickness flexible silicone (SENKEI, Hubei Province, China) to simulate GORE-Tex implants. GORE-Tex implantation was chosen for this simulation as all laryngologist evaluators exclusively use this material in their respective practices for medialization thyroplasty.

Figure 2:

Full medialization thyroplasty simulator. (A) Assembled simulator, including full larynx, head and neck manikin, and borescope. (B) Demonstration of medialization of silicone vocal fold.

The simulator was reviewed by laryngology fellows and fellowship-trained laryngologists. All reviewers completed a modified Michigan Standard Simulation Experience Scale (MiSSES)⁸ to comment on subjective experience with the simulator and evaluate anatomic fidelity, educational value, and overall value using a five-point Likert scale. Each numerical value on the scale corresponded to a qualitative statement: “strongly disagree” (lowest), “somewhat disagree,” “neutral,” “somewhat agree,” and “strongly agree” (highest). Internal validity of the modified MiSSES was assessed using the Cronbach’s α. Interrater reliability was assessed using two-way agreement, average measure intraclass correlation (ICC).

Results

Five attending laryngologists and three laryngology fellows evaluated the thyroplasty simulator in a hands-on assessment and completed the modified MiSSES rubric (Table 1). As previously demonstrated, the scale had high levels of internal consistency (Cronbach’s α = 0.902) and inter-rater reliability (ICC = 0.877, 95% CI = 0.679–0.975). The model was highly rated for measures of educational value and overall value, with numeric ratings consistently above 4.0. The simulator was also rated moderately well for anatomic fidelity, especially for realistic anatomic features. Raters were more neutral about categories relating to the realism of materials used in the simulator, including the pliability of the silicone endolarynx and the density of the heat-treated polylactic acid cartilage framework. Qualitative comments described strengths of the model to include good visual feedback of seeing medialization with implant placement, as well as realistic appearance and ease of use. Rater-identified areas for improvement included the elasticity of the silicone soft tissue and lack of pathologic variations of glottic insufficiency (Table 2).

Table 1:

Summary of Scores from the Modified Michigan Standardized Simulation Experience Scale

	Mean Score (SD)
Anatomic fidelity
The simulator has adequately realistic features.	4.3 (0.5)
The combination of the rigid plastic framework and soft silicone insert adequately represents human laryngeal anatomy.	4.3 (0.5)
The silicone soft tissue pliability when placing the implant is adequately similar to that of real human tissue.	3.6 (1.1)
The rigid plastic framework is adequately similar to human thyroid cartilage when drilled.	3.7 (1.1)
Educational Value
The simulator is a good training tool for developing skills in medialization laryngoplasty.	4.4 (0.5)
The simulator is useful for teaching the size and placement of the thyroid cartilage window in both female and male larynges.	4.9 (0.4)
The simulator is useful for teaching the placement of a GORE-Tex insert.	4.6 (0.5)
Overall Value
Overall, the simulator is a good educational device.	4.7 (0.5)

Table 2:

Summary of Qualitative Feedback

Strengths of model	Visual feedback of vocal fold medialization with implant placement Realistic scale, appearance, and feel Pliable soft tissue Reproducibility, ease of use
Areas for improvement	Silicone more flexible and elastic than human tissue Lack of simulated surgical exposure of thyroid cartilage Model based on innervated larynx, lack of pathology variations

The average cost of silicone required to produce one endolaryngeal insert was $1.13. The average cost of heat-treated polylactic acid needed for one laryngeal cartilage framework was $2.96, making the total materials cost per larynx $4.09. The cost of one 1-inch x 6-inch silicone implant sheet was $0.45. Other materials, including the printer, manikin (material cost: $10.43), borescope, and injection molds (material cost: $1.54), were durable and reusable.

Discussion

Simulation has proven to be a valuable training tool across all medical specialties, with special significance in surgical specialties that require repeated procedural practice and hands-on teaching.⁹ With the changes put forth in 2003 by the Accreditation Council for Graduate Medical Education and the advent of 80-hour per week limitations,¹ as well as trends towards using competence-based assessment for trainees,² the need for educational adjuncts has continued to grow. Surgical educators have been challenged to ensure high-quality training for residents with fewer hours in the operating room. Additionally, educational challenges emerged during the COVID-19 pandemic as elective surgeries were cancelled and residents were redeployed to assist with critical hospital needs, affecting the total amount of cases surgical residents were able to participate in.¹⁰ This further highlighted the need for innovative tools to continue providing quality training for residents outside of the traditional operating room setting.

In otolaryngology, several simulators have emerged and been validated as effective devices for trainees, including those for mastoidectomy, endoscopic sinus surgery, and peritonsillar abscess drainage.¹¹ In addition to representing a wide variety of procedures, the existing body of otolaryngology simulators also utilizes a vast range of materials to create these models, each with their respective strengths. Human cadaver and animal models, for example, allow for high anatomic fidelity and good haptic feedback. However, access to human and animal cadavers may be limited, and cost may be prohibitive for institutions with fewer resources. Other simulators, such as those made of household items (e.g. construction paper) are generally low-cost and easily reproducible. However, such materials may create models with less anatomic fidelity and less akin to real-world clinical scenarios.

Three-dimensional printing has emerged as an effective tool for the creation of simulators with the potential of both high fidelity and low cost. As the world of 3D-printing continues to grow, printers and plastic printing filaments have become increasingly affordable and versatile. For more complex anatomic models, such as a recent bronchoscopy simulator,¹² large industrial 3D printers can produce objects using multiple 3D-printed filaments at once, thereby creating a realistic range of textures and density. Other models, such as a percutaneous injection laryngoplasty simulator,⁶ have utilized less expensive desktop 3D printers, using one type of plastic filament at a time, maintaining high-fidelity with laryngeal anatomy, despite their simplicity and low-cost.

In the present study, we established a novel 3D-printed medialization thyroplasty simulator that draws from the design of Lee et al.⁶ to create a similarly high-fidelity, low-cost model intended for use by otolaryngologists at any level of training. Our cohort of evaluators, comprised of laryngology fellows and fellowship-trained laryngologists, reported that this simulator had high value as an educational tool in its current design. While this iteration utilized GORE-Tex implantation in the thyroplasty protocol, we believe that our model would be similarly effective in simulating silastic implantation. Regardless of implantation material used, with the added challenges of having an awake patient while performing medialization thyroplasty, this simulator may be a useful educational platform on which trainees can practice and gain comfort with medialization thyroplasty in a low-stakes environment, without concern for the experience of a patient under conscious sedation.

The cost of materials and open-source design of our simulator may have broad implications for access. Three-dimensional printing is much more affordable nowadays thanks to the availability of lower-cost and high accuracy smaller printers. Some 3D printers, such as the one used to create this thyroplasty simulator (Creality Ender-3, Shenzhen, China), cost as little as $200 USD. By showing that this simulator can be produced by one such desktop printer with low-cost plastic filament and silicone, we demonstrated the low cost of the production process. By adhering to an open-source design previously published on the Wikifactory website with accompanying step-by-step instructions, we hope that any institution will be able to replicate the model with relative ease.

There are limitations to our thyroplasty simulator that were identified by our raters. Although most rated anatomic fidelity of the model neutrally or positively, it was also the domain in which most suggestions for improvement were made. For example, though our raters appreciated the presence of the soft tissue insert and real-time feedback of watching vocal fold medialization, the density and elasticity of silicone were identified as being greater than that of human soft tissue, ultimately affecting the simulated experience of placing the implant. Another limitation is that the two versions of our simulator representing the sexes were of differing sizes, but used the same anatomic proportions. In reality, thyroid cartilage measurements, such as the transverse diameter and the thyroid angle, differ between males and females¹³ and require sex-dependent adjustment to thyroplasty window placement. Though the overall size differences of our models create different user experiences between sexes, our simulator could be improved by incorporating sex-specific dimensional differences.

In being rated well for anatomic fidelity and very highly for educational and overall value by experts in laryngology, we have demonstrated face validity for this thyroplasty simulator. Moving forward, we hope to address predictive validity of our model amongst trainees using a prospective trial to determine if training with the simulator improves skills specific to medialization thyroplasty. Furthermore, future efforts can be made to refine the materials and sex-dependent dimensions of the simulator to continue to improve the quality of this novel educational tool.

Conclusion

Training of surgical procedures, such as medialization thyroplasty, on awake patients poses challenges to educators and trainees. 3D-printed simulators provide opportunity to practice such procedures in low-stakes settings. We described the design of high-fidelity 3D-printed simulator for medialization thyroplasty training and demonstrated its face validity. The low-cost, open-source design has broad implications for universal access of this training platform. In the future, we hope to prove content and construct validity of our simulator amongst otolaryngology trainees and attendings using a prospective trial.