key: cord-0980893-dm7otkwr
authors: Razavi, Christopher; Galaiya, Deepa; Vafaee, Seena; Yin, Rui; Carey, John P.; Taylor, Russell H.; Creighton, Francis X.
title: Three dimensional printing of a low‐cost middle‐ear training model for surgical management of otosclerosis
date: 2021-09-01
journal: Laryngoscope Investig Otolaryngol
DOI: 10.1002/lio2.646
sha: e203505549cbfc06c15c2b8c5f455792b2668ca3
doc_id: 980893
cord_uid: dm7otkwr

BACKGROUND: Surgical management of otosclerosis is technically challenging with studies demonstrating that outcomes are commensurate with surgical experience. Moreover, experts apply less force on the ossicular chain during prosthesis placement than their novice counterparts. Given the predicted decreasing patient pool and the rising cost of human temporal bone specimens it has become more challenging for trainees to receive adequate intraoperative or laboratory‐based experience in this procedure. As such, there is a need for a low‐cost training model for the procedure. Here we describe such a model. METHODS: A surgical model of the middle ear was designed using computer aided design (CAD) software. The model consists of four components, the superior three dimensional (3D)‐printed component representing the external auditory canal, a 90° torsion spring representing the incus, a 3D‐printed base with a stapedotomy underlying the torsion spring, and a 3D‐printed phone holder to facilitate video‐recording of trials and subsequent calculation of the force applied on the modeled incus. Force applied on the incus is calculated based on Hooke's Law from post‐trial computer‐vision analysis of recorded video following experimental determination of the spring constant of the modeled incus. RESULTS: The described model was manufactured with a total cost of $56.50. The spring constant was experimentally determined to be 97.0 mN mm/deg, resulting in an ability to detect force applied to the modeled incus across a range of 1.2 to 5200 mN. CONCLUSIONS: We have created a low‐cost middle‐ear training model with measurable objective performance outcomes. The range of detectable force exceeds expected values for the task. Level of Evidence: IV.

Surgical management of otosclerosis is a technically challenging procedure which can yield excellent outcomes in expert hands. However, complications can also result irreversible sensorineural hearing and vestibular loss. Studies have demonstrated that outcomes are commensurate with surgical experience, with experienced otologists achieving a postoperative air-bone gap of <10 dB in up to 95% of cases, while trainees achieve this same benchmark in only 62% to 87% of their respective cases. [1] [2] [3] [4] [5] [6] In fact, the learning curve for the procedure has been estimated to be between 60 and 80 cases, a stark contrast to the minimum number of 10 ossicular chain reconstructions (OCRs) required to graduate Otolaryngology-Head & Neck Surgery (OHNS) and the additional 20 OCRs required for Neurotology residencies as per the Accreditation Council for Graduate Medical Education (ACGME). 7 To complicate matters, the predicted decreasing patient pool, as well as the rising cost of human temporal bone specimens, have made it more challenging for trainees to receive adequate intraoperative or laboratory-based experience for this procedure. [8] [9] [10] As such, many middle ear simulators have been proposed over the last 20 years. However, all are limited in their ability to provide objective measurable outcomes, anatomic fidelity, cost, or a combination of these factors. [10] [11] [12] [13] Here, we describe a low-cost threedimensionally printed middle ear model, which provides objective data regarding force exerted on the modeled incus during stapes prosthesis placement and crimping. 

As operative volume for otosclerosis decreases, models such as the one described will be invaluable to trainees and ultimately to patients, as we aim to maintain excellent outcomes with stapedectomy in a new generation of surgeons. Furthermore, as the COVID-19 pandemic has demonstrated, there is a growing need for surgical training opportunities outside the operating theatre. Although many OHNS programs have provided extracurricular educational opportunities to trainees via didactic virtual lectures during the pandemic, these fall short in facilitating technical skill development. This is of concern for technically demanding procedures, such as stapedectomy, particularly when noting that a poor hearing outcome after stapes surgery is the most litigated case within F I G U R E 2 Experimental calculation of torsional spring force constant. The spring was displaced by a known magnitude. A computer vision script was then used to determine angular displacement of the spring and the length of the moment arm. This process was repeated 20 times with different displacement magnitudes to determine the torsional spring constant F I G U R E 3 Demonstration of training model in use. The user can be seen placing a piston prosthesis on the modeled incus. The calibration marker (in black) can be seen on the right side of the image otologic surgery. 15 High fidelity surgical simulators may help minimize the threats to trainee education that decreasing case volumes and operative independence will have on the future of our specialty.

With the advent of laser-assisted stapedectomy and footplate fenestration techniques, many Otologist suggest that the most technically challenging aspect of the case is the placement and crimping of the stapes prosthesis. 5, 11 As such, some argue that the inferior outcomes seen in trainees with the procedure is therefore due to their less practiced hands with manipulation of the prosthesis itself. 4 Thus, a middle-ear model placing emphasis on prosthesis manipulation with an objective measurable outcome would be of great value to trainees. The model we describe provides these capabilities while also being low-cost. Prior studies have demonstrated that novices apply on average 139 and 522 mN of force, while their expert counterparts apply 42 and 204 mN of force in prosthesis placement and crimping, respectively. 16 The range of force that can be detected with this model is therefore more than adequate for those generally applied to the incus during middle ear prosthesis manipulation for both novices and experts.

Several studies have demonstrated that expert surgeons exert less force during procedural tasks than novice/junior surgeons. [16] [17] [18] Moreover, the force transmitted to the inner ear during middle ear surgery is often cited as a potential cause of sensorineural hearing loss during stapedectomy. [16] [17] [18] As such, improved performance in our model, which provides objective outcome measures that can be tracked, may directly translate to improved intraoperative performance, though this will need to be studied further.

Future studies will be needed to further validate our computer vision script and test its ability to be disseminated among training programs.

These studies will need to examine placement and crimping forces, measured from our computer vision script, between surgeons of varying skill level, to ensure they are consistent with our previously studies. 15 

We have developed a low-cost high-fidelity training model for the surgical management of otosclerosis. This model provides users with objective, and relevant, outcome measures that can be trended and improved upon. Models such as this are invaluable tools to supplement trainee operative education given the growing threats to resident operative opportunities.

This study was supported by NIDCD T32 DC000027.

A 15-year report on fenestration of the oval window

Eighteen years experience in stapedectomy. The case for the small fenestra operation

Audit of stapedectomy results in a teaching hospital

Prospective study of residentperformed stapedectomy

Stapedectomy in residency training

Stapes surgery in residency: the UFPR clinical hospital experience

The learning curve in stapes surgery and its implication to training

Trends and profiles in stapes surgery

Review of temporal bone dissection teaching: how it was, is and will be

A middle-ear simulator for practicing prosthesis placement for otosclerosis surgery using ward-based materials

Incus and stapes footplate simulator

High-fidelity, inexpensive surgical middle ear simulator

Modifications to a 3D-printed temporal bone model for augmented stapes fixation surgery teaching

Anatomy of the distal incus in humans

Stapes surgery in a residency training program

Applied force during piston prosthesis placement in a 3D-printed model: freehand vs robotassisted techniques

Measuring the forces of middle ear surgery; evaluating a novel force-detection instrument

Task performance in stapedotomy: comparison between surgeons of different experience levels

Three dimensional printing of a low-cost middle-ear training model for surgical management of otosclerosis

The authors declare no potential conflict of interest.

https://orcid.org/0000-0002-1616-0135Francis X. Creighton https://orcid.org/0000-0003-3131-1162