Cadaver Head Holder for Transoral Surgical Simulation

The Laryngoscope C 2018 The American Laryngological, V

Rhinological and Otological Society, Inc.

How I Do It

Cadaver Head Holder for Transoral Surgical Simulation Jiyoo Chang, BA; Xiaotian Wu, BE; Peter W. Kahng, BA; Ryan J. Halter, PhD; Joseph A. Paydarfar, MD

INTRODUCTION Cadaver-based simulation offers hands-on anatomical exploration to help surgeons practice and develop techniques in a realistic laboratory environment that can then be translated to the clinical setting. For teaching, research, and simulation of transoral robotic surgery (TOS) and transoral laser microsurgery (TLM) use of a cadaver head and neck unit by itself is not feasible due to difficulties in securing the head and providing the proper extension of the neck. As a result, a cadaver head and torso unit is required to provide the necessary stability and neck extension. This limitation adds further cost and storage requirements associated with the purchase and housing of the combined head and torso unit. In this report, a simple and cost-effective cadaver head-holding system is presented that provides the stability of the torso and adjustability for neck extension and head manipulation that accurately models the maneuvers required for operative laryngoscopy and other transoral procedures.

MATERIALS AND METHODS Cadaver Head-Holding System Design The cadaver head holder is comprised of three key components: base, neck, and cap (Fig. 1). The base consists of a wooden support and an adjustable Advanced Drainage Systems (ADS) PolyFlex pipe (Advanced Drainage Systems, Hilliard,

From the Thayer School of Engineering (J.C., X.W., R.J.H., J.A.P.); Geisel School of Medicine (P.W.K.), Dartmouth College, Hanover, New Hampshire; Department of Surgery (R.J.H.) and Section of Otolaryngology, Audiology and Maxillofacial Surgery, Department of Surgery (J.A.P.), Dartmouth-Hitchcock Medical Center, Geisel School of Medicine, Lebanon, New Hampshire, U.S.A. Editor’s Note: This Manuscript was accepted for publication February 2, 2018. Presented at the Simulation Showcase and Reception, American Academy of Otolaryngology–Head and Neck Surgery Foundation Annual Meeting, Chicago, Illinois, U.S.A., September 10–13, 2017. This work was funded by the Norris Cotton Cancer Center Development Fund (Prouty Pilot Grants), Dartmouth Hitchcock Medical Center, Lebanon, New Hampshire, U.S.A. The authors have no other funding, financial relationships, or conflicts of interest to disclose. Send correspondence to Joseph A. Paydarfar, MD, Section of Otolaryngology, Audiology and Maxillofacial Surgery, Dartmouth-Hitchcock Medical Center, 1 Medical Center Drive, Lebanon, NH 03756. E-mail: [email protected] DOI: 10.1002/lary.27161

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OH) (i.e., “spine”) fixed to the support through a bolt acting as a hinge joint. The angle of the spine-mimicking tube determines the degree of neck extension and can be fixed by an optional second bolt. The base is secured with C clamps to a table or other work surface. The neck is a standard schedule 40 plain polyvinyl chloride (PVC) tube that acts as a cylindrical joint with the base. The neck attaches to the cadaver head via the cap, which is secure to the neck with a single machine screw. The cap consists of a schedule 40 PVC socket cap that connects to the vertebral body of the cadaver head with three wood screws. The cap/neck assembly slides onto the slightly smaller diameter PolyFlex spine of the base; this loose fit enables rotation about the long axis of the neck tube. For suspension laryngoscopy, the suspension arm typically rests on the patient’s chest or a platform that attaches to the bed and is situated over the chest. This can be simulated with any small mobile platform on which the suspension arm can rest (Fig. 2B). A detailed instruction manual of the design and fabrication of this device is available at: https://engineering.dartmouth. edu/halter-lab/cadaver-head-holder.

System Validation The system was trialed on fresh-frozen cadaver heads. All heads were specified to have the amputation occur below the level of the larynx. The heads were thawed for 36 hours before use. After the cadaver head was attached to the simulator, the neck was extended to simulate head position during laryngoscopy. Transoral access to the pharynx and larynx was simulated using a computed tomography (CT)–compatible polymer laryngoscope,1 a Lindholm (Karl Storz, Tuttlingen, Germany) operating laryngoscope placed in suspension, and a Crowe-Davis retractor suspended from a Mayo stand. Neck extension and scope position were assessed using CT imaging with the polymer laryngoscope in suspension.

Simulation Survey A survey was distributed to faculty and resident otolaryngologists to assess how the simulated cadaver-based laryngoscopy compared with laryngoscopy in a live patient. Quality of simulation was rated on a scale of 1 to 5, with 5 being very similar to surgical laryngoscopy.

RESULTS The cadaver head-holding system was trialed on four fresh-frozen cadaver heads weighing 4.12 to 5.75 kg. The cap was successfully secured to the vertebral body Chang et al.: Cadaver Head Holder for TOS Simulation

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Fig. 1. Three-dimensional computer-aided drawing model of components and assembled cadaver head holder system. ADS 5 Advanced Drainage Systems [Color figure can be viewed in the online issue, which is available at www.laryngoscope.com.]

in all four heads. Because the cap is opaque, the process of attaching it often required several screw holes due to the inability to visualize the vertebral body during the drilling process. Despite this limitation, the cap was sufficiently secure to maintain attachment to the cadaver head during multiple laryngoscopies and during transport of the head, which was performed by grasping the neck component. When attached to the base, the heads were easily placed in extension and rotation. Figure 2 demonstrates the performance of the head-holding

system during direct laryngoscopy, suspension laryngoscopy, and with placement of a Crowe-Davis retractor. As shown in Figure 3, the position of the cadaver head during suspension laryngoscopy provided a similar field of endoscopic visualization of the cadaver larynx and pharynx as compared to that of in vivo patient endoscopy. Sagittal CT imaging obtained during suspension laryngoscopy with a CT-compatible laryngoscope from a cadaver head and neck attached to the head holding system and from an in vivo patient head and neck

Fig. 2. Human cadaver head attached to the head holding system during (A) direct laryngoscopy, (B) suspension laryngoscopy, and (C) with Crow-Davis retractor. [Color figure can be viewed in the online issue, which is available at www.laryngoscope.com.]


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Chang et al.: Cadaver Head Holder for TOS Simulation

Fig. 3. The endoscopic view of the larynx and pharynx in a cadaver versus a patient. [Color figure can be viewed in the online issue, which is available at www.laryngoscope.com.]

(Fig. 4) highlight the anatomic similarities between the two scenarios in terms of extension, scope position, and angle of the neck. Surveys regarding the laryngoscopic view with the head-holding system were collected from four attending and three resident otolaryngologists (postgraduate year 3 and greater). The mean response for the quality of the suspension system view when compared to surgical laryngoscopy of a patient was 4.3 out of 5, with 5 being very similar to surgical laryngoscopies.

Cap Modification To improve ease and accuracy of screw placement into the vertebral body, a custom transparent Plexiglas plate was designed and fabricated to enable visualization of the vertebral body during the drilling process. To implement this upgrade, basic machining skills and additional material costs are required. The dimensions and design of this modification are available on the website listed in the Materials and Methods section.

DISCUSSION Cadaver-based teaching and simulation plays an important role in surgical education and research.2,3 In otolaryngology, harvesting and dissection of cadaveric temporal bones is considered a requirement for otolaryngologists in training.4 Full cadaver heads are commonly used for sinus and skull base simulation. For simulation of laryngeal surgery, several authors have described devices for holding the cadaver larynx.

Paczona introduced a device constructed of wooden boxes that holds the cadaveric larynx and a laryngoscope in place5; Sani and McCulloch described a steel larynx holder that incorporates a laryngoscope and is adjustable in height and angle.6 Hybrid models with nonhuman larynges have also been described.7 However, for simulation of more extensive procedures involving the larynx and pharynx, such as with TLM and TORS, combined cadaver head and torso units are often required to provide the necessary stability as well as neck extension and rotation. As more programs incorporate routine TORS training into the residency curriculum,8 cost and storage requirements associated with the cadaver head/ torso unit become a significant consideration. The head-holding system presented in this report provides a cost-effective solution for simulating laryngoscopy and other transoral procedures. A cadaver head and neck can be used in lieu of the head/torso unit, thereby reducing cost and storage requirements significantly. This system is relatively simple to build and easy to maintain. For the version of the system in which a standard PVC end cap is used, no machine shop skill or equipment is required; basic machine shop skill is necessary to fabricate the transparent Plexiglas mounting plate. The materials to build the system can be obtained easily at any home improvement store (e.g., Home Depot or Lowes). For the prototype presented in this report, material cost was less than $20 total. From a functionality standpoint, the system allows the surgeon to easily modify how much the cadaver neck is hyperextended and rotated after the laryngoscope is inserted to simulate a real patient during laryngoscopy. As seen from the endoscopic and CT images, exposure and visualization is comparable to a live patient. Based on the results of the survey, surgeons felt that this cadaver-based simulation model provided an accurate view of the laryngeal anatomy to help replicate a realistic experience of surgical laryngoscopy, further supporting its use as a surgical training aide and research tool.

CONCLUSION The cadaver head-holding system presented in this report is cost-effective and easy to construct. This system enables the use of only a cadaver head and neck while still providing the necessary stability as well as neck extension and head rotation required to accurately simulate transoral procedures such as TLM and TORS. This approach significantly reduces cadaver acquisition cost and storage requirements when compared with the head/torso unit typically required for these simulations.

Acknowledgments

Fig. 4. Comparison of sagittal computed tomography (CT) images of the cadaver head with a patient using a CT-compatible polymer laryngoscope (highlighted in yellow). [Color figure can be viewed in the online issue, which is available at www.laryngoscope.com.]


The authors thank Michaela Whitty, Michael Pearl, and John Peiffer from the Dartmouth Hitchcock Center for Surgical Innovation for their support. This project would not have been possible without their efforts. In addition, the authors thank Douglas McKenney from the Engineering Department at Dartmouth Hitchcock Medical Center for machine shop assistance. Chang et al.: Cadaver Head Holder for TOS Simulation

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BIBLIOGRAPHY 1. Paydarfar JA, Wu X, Halter RJ. MRI- and CT-compatible polymer laryngoscope: a step toward image-guided transoral surgery. Otolaryngol Head Neck Surg 2016;610:1–3. 2. Sharma G, Aycart MA, Najjar PA, et al. A cadaveric procedural anatomy course enhances operative competence. J Surg Res 2016;201:22–28. 3. Kim SC, Fisher JG, Delman KA, Hinman JM, Srinivasan JK. Cadaverbased simulation increases resident confidence, initial exposure to fundamental techniques, and may augment operative autonomy. J Surg Educ 2016;73:e33–e41.


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4. George AP, De R. Review of temporal bone dissection teaching: how it was, is and will be. J Laryngol Otol 2010;124:119. 5. Paczona R. A cadaver larynx holder for teaching laryngomicrosurgery. J Laryngol Otol 1997;111:56–57. 6. Mohamed AS, McCulloch TM. A larynx holder: a device for training in microlaryngeal surgery. Laryngoscope 2004;114:1128–1129. 7. Chan CY, Lau DPC. Simulators and models for laryngeal laser surgery and laser myringotomy. Laryngoscope 2016;126:2089–2091. 8. Sperry SM, O’Malley BW, Weinstein GS. The University of Pennsylvania curriculum for training otorhinolaryngology residents in transoral robotic surgery. ORL J Otorhinolaryngol Relat Spec 2014;76:342–352.

Chang et al.: Cadaver Head Holder for TOS Simulation