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Simulation of laryngotracheal reconstruction with 3D‐printed models and porcine cadaveric models

Abstract Objectives Laryngotracheal reconstruction (LTR) is a complex operation used to treat subglottic stenosis. The use of simulator models is a valuable tool in surgical trainee education, particularly for operations such as LTR that are less common outside high‐volume centers. Three‐dimensional (3D) printing of the human airway may provide an effective and more accessible alternative to porcine cadaveric models. The objective of this study is to compare the educational value of a 3D‐printed model and a porcine cadaveric model as LTR simulation methods. Methods Simulated LTR procedures were completed by 12 otolaryngology residents and a faculty physician on the cadaveric model and the 3D‐printed simulator model. Both models were evaluated by fellowship‐trained pediatric otolaryngologists to establish construct validity. Pre‐procedure surveys of participants evaluated confidence and attitude toward models and post‐procedure surveys evaluated confidence, overall impressions, relevance, content validity, and face validity. Results Participants reported a similar mean increase in confidence after performing LTR on the 3D‐printed model (14%) and cadaveric model (11%). Participants rated both models similarly for utility as an overall training tool and in teaching surgical planning and improving operative techniques. However, participants found the 3D‐printed model more useful for teaching anatomy (p = .047). Conclusion 3D‐printed models have practical benefits over cadaveric models; they do not decompose and can be custom made to model a disease state such as subglottic stenosis. Participants reported a similar mean increase in confidence after using either simulation. The 3D‐printed model is a promising simulation candidate as it compares well to an animal model and has the advantage of being more anatomically true to pediatric patients. Level of Evidence: Level 2.


| INTRODUCTION
Laryngotracheal reconstruction (LTR) is a complex operation used to treat subglottic and tracheal stenosis. The most common etiology of pediatric airway stenosis is prolonged endotracheal intubation. Airway management options for subglottic and tracheal stenosis were historically limited to tracheostomy until the development of open laryngeal approaches in the 1900s. The term "laryngotracheal reconstruction" was first used in 1953 by John Conley. 1 LTR is a complex surgical operation that, in the modern era, is performed mainly by fellowship trained pediatric otolaryngologists at dedicated children's hospitals.
The use of simulator models is a valuable tool in resident trainee education, particularly in highly technical surgical specialties such as otolaryngology. 2,3 As discussed, LTR is a highly complex operation that is relatively uncommonly performed at locations outside high-volume LTR hospitals. To close the gap in education between higher volume and lower volume centers, simulation may be a useful tool. Currently, validated and commercially available animal models for LTR simulation training include suckling-pig and lamb. 4,5 The rabbit model has been well studied, but not validated as a simulation tool. 4 A systematic review of available animal models in 2019 concluded that while a rabbit airway is an appropriate size for a neonate or younger child's airway, differences in laryngeal anatomy made LTR simulation difficult. Despite the larger size, sheep, pig, and goat larynges had more similar anatomy to human laryngotracheal complexes. 5 Three-dimensional (3D) printing of the human airway has been developed to provide an effective and more accessible alternative to animal or cadaveric airway models. 6 The aim of this study is to directly compare a more traditional animal model to a 3D-printed model for the simulation of laryngotracheal reconstruction.

| MATERIALS AND METHODS
This prospective cohort study was deemed exempt by the Indiana University Institutional Review Board. All participants provided informed consent.

| Participants
Simulated LTR procedures were completed by 12 otolaryngology residents and a faculty physician on the porcine cadaveric model and the 3D-printed simulator model (n = 13). Resident trainees ranged from PGY 1 to PGY 5 levels, with 2 or more residents at each level of training. The faculty participant completed each model, while resident participants were randomized and matched by PGY level to complete either the 3D-printed model (n = 7) or the porcine cadaveric model (n = 7).

| Simulation and surveys
The 3D printed model in this study consisted of two parts, a pediatric sized laryngotracheal complex and a pediatric sized rib cartilage ( Figure 1). Each airway model had grade III subglottic stenosis ( Figure 2). Model manufacturing has been previously described. 6 A porcine cadaveric model was used in this study, which consisted of a pig larynx and trachea and cartilaginous rib ( Figure 3).
The porcine models did not have simulated subglottic stenosis.
Prior to beginning the simulation, participants were instructed to watch a 10-min instructional video from the University of Michigan with specific steps of performing LTR. 6 Participants were instructed to perform anterior airway grafting only (Figures 4 and 5).
Each participant completed a pre-procedure and post-procedure survey. Pre-procedure surveys of participants evaluated experience with LTR, perceived expertise in performing LTR, confidence performing LTR and attitudes toward simulators.
Post-procedure surveys evaluated perceived expertise in performing LTR, confidence performing LTR, value of the simulator, face validity, global content validity, task specific content validity, relevance of the model to practice. Participants were also given an option to report on the pros and cons of the model they used.   All participants rated their pre-simulation confidence levels in performing LTR, means of 25% in the porcine cadaveric model and 20.83% in the 3D printed, without significant difference (Table 1). On an integer scale of 1-5, participants also rated their surgical expertise in performing an LTR overall, making the anterior airway incision, fashioning the anterior graft, and integrating the anterior graft into the airway. No significant difference between groups was found on their surgical expertise prior to simulation ( Table 2).

| RESULTS
After performing LTR simulation, participants were asked to again rate their confidence and surgical expertise by the same criteria (Table 2). Confidence in performing LTR increased to 37.5% in both the porcine and 3D-printed model groups. The increase in confidence was not statistically different between groups (Table 1). Participants were also asked to rate the relevance of the model to their practice. There was no significant difference between the groups (Table 3).

| Face validity
Face validity was assessed by all participants (n = 13) and results are displayed in Table 4. Face validity is a subjective type of validity, and generally used in the early stages of development. 8

| Content validity
Both global and task specific content validity were evaluated by all participants (n = 13, Table 5). No significant difference was seen between groups with the exception of usefulness if teaching anatomy, which favored the 3D printed model (p = .047).

| DISCUSSION
Simulation training for residents has been shown to improve patient outcomes. 9 While simulation does not replace clinical training, it can provide trainees with increased confidence. 7 While otolaryngology resident education has become increasingly standardized, certain operations such as LTR are done in higher volumes at certain centers.
Simulation can be highly beneficial to improve resident confidence in performing a less common, high risk airway procedure.
This is the first published study, to the authors' knowledge, to directly compare a 3D printed model to an animal model for simulation of laryngotracheal reconstruction. Both models have been validated independently 4,6 and each has distinct pros and cons.
Participants had similar increases in confidence and expertise after performing either simulation in this study (0.60 and 0.21, respectively), and found both models similarly relevant to their practice.
With any new tool, establishing validity is an important step prior to wider adoption. This study measured face, content, and construct validity. Face validity slightly favored the porcine model, although both models had good face validity overall (Table 3). Global and task specific validity was high for both models ( Table 4). The final measure of validity in this study was construct validity, which was established as high for both models.
3D-printed models have many practical benefits. They do not decompose, which means they can be saved for future use/reference.
Progress may be tracked and preserved on a 3D-printed model. In terms of accessibility, cost per 3D-printed model is approximately $2.60 USD 6 while cost per porcine cadaver model ranges from $6-8 USD when purchased from online distributors. 10,11 Since 3D-printed models do not decompose or require special storage, they can be shipped from a facility that 3D prints the models and stored easily. In contrast, the porcine model requires special packaging and shipping materials, as well as storage in a refrigerator or freezer to stay fresh.
The lower cost and more straightforward storage of 3D-printed models are a major benefit to this model. There is also an ethical concern with using animal models regarding loss of animal life when alternative options exist.
Another benefit is that a 3D-printed model can be customized to replicate specific airway scenarios and grades of subglottic stenosis to allow for improved preoperative planning. 6

| Limitations
This was a single institution study at a relatively low volume LTR Faculty ratings for the tasks had good interrater reliability for the porcine model, but relatively worse reliability for the 3D-printed model. Given that the porcine model is a more established simulation and teaching format, it may have been more familiar for evaluation.
The porcine model also could not be evaluated for airway patency as there was no pre-existing subglottic stenosis. For future studies, rating criteria should be more clearly established for both models, but particularly the 3D-printed model.
Ultimately, the most useful validity measure for a test or simulation is predictive validity. Predictive validity is the extent to which performance on a test predicts actual performance, in this case whether better performance on the simulator predicts better performance in the operating room. 8 This would be the most clinically meaningful validity to establish and would be important to evaluate in further studies.

| CONCLUSIONS
This study, to the authors' knowledge, is the first to directly compare 3D-printed and animal models for simulation of LTR. Participants reported a similar mean increase in confidence after using either simulation. Each model was rated for face, content, and construct validity with good results. The porcine model was rated higher in anatomic and cartilage realism, but participants found both models overall useful for LTR simulation.
The 3D-printed model is a promising simulation candidate as it compares well to an animal model and has the advantage of being more anatomically true to pediatric patients. In addition, 3D-printed models have practical benefits over cadaveric models; they do not decompose, and can be custom made to model a disease state such as subglottic stenosis. 3D-printed simulation models are a promising, accessible option in resident education.

FUNDING INFORMATION
No sources of financial support or external funding.

CONFLICT OF INTEREST
The authors have no conflicts of interest to disclose. David Zopf is a cofounder of University of Michigan affiliated startup MakeMedical LLC, which provided no financial support for the research.