Mémoire du diplôme interuniversitaire de pédagogie médicale

Conception d’un simulateur de chirurgie otologique

Dr Yann Nguyen

Septembre 2016

Résumé

Introduction: Les résultats fonctionnels et le risque de complications de la chirurgie de

l’otospongiose est dépendant de l’expérience chirurgicale. L’acquisition de la technique

chirurgicale et la réduction de la courbe d’apprentissage sont essentiel pour les internes en

formation. Les os temporaux artificiels en impression 3D ont remplacé les pièces anatomiques

pour l’enseignement du fraisage de l’os temporal mais ne sont pas adapté à l’enseignement de

la chirurgie de l’oreille moyenne. Le but de ce travail a été d’adapter un os temporal artificiel

afin qu’il puisse servir à l’enseignement de la gestuelle pour la chirurgie de l’otospongiose et

d’évaluer cet outil.

Matériel et méthodes: Nous avons modifié un os temporal artificiel commercialisé en

remplaçant l’enclume et l’étrier par nos propres modèles en impression 3D. L’enclume a été

fixée à un capteur d’effort 6-axes. L’étrier a été préparé par une ouverture platinaire puis fixé

à un capteur 1 axe. Six chirurgiens juniors (internes) et sept chirurgiens seniors (PHs, chefs de

clinique ou assistants) ont participé à l’étude de validation en posant une prothèse ossiculaire

d’otospongiose puis en la serrant sur la longue apophyse de l’enclume, reproduisant ainsi la

technique chirurgicale de référence. La durée de la tâche et les forces appliquées à l’enclume

et l’étrier ont été mesurées et analysées.

Résultats: Aucune différence entre le groupe des chirurgiens juniors et des seniors n’a été

observée pour la durée de la tâche et les forces appliquées sur l’enclume lors de la pose de la

prothèse et son placement. Des forces plus faibles ont été appliquées sur l’étrier par le groupe

des chirurgiens seniors comparés au groupe des chirurgiens juniors pendant la pose (junior vs

senior group, 328±202.9 mN vs 80±99.6 mN p=0.008) et le serrage de la prothèse (junior vs

senior group, 565±233 mN vs 66±48.6 mN p=0.02).

Conclusion: Nous avons décrit un nouvel outil d’enseignement pour la chirurgie de

l’otospongiose à partir d’un os temporal artificiel modifié afin de permettre la fixation de

capteurs d’effort sur l’enclume et l’étrier. Cet outil pourrait être utilisé comme outil

d’entrainement pour aider les internes à améliorer leur confiance en eux et à autoévaluer leur

progression avec des données d’évaluation mesurables.

Modifications of a 3D-Printed Temporal Bone Model for Augmented Otosclerosis Surgery

Teaching

Yann Nguyen 1,2,3, Elisabeth Mamelle1,2,3, Daniele De Seta 1,2,3, Daniele Bernardeschi1,2,3, Olivier

Sterkers 1,2,3, Renato Torres 1,2

1. Sorbonne Universities, UPMC Univ. Paris 06, Paris, France

2. Inserm, UMR S-1159, “Minimally Invasive Robot-based Hearing Rehabilitation”, 75018, Paris,

France

3. AP-HP, Pitié-Salpêtrière Hospital, Otorhinolaryngology Department, Unit of Otology, Auditory

Implants and Skull Base Surgery, 75013, Paris, France

Corresponding author:

Yann Nguyen, M.D., PhD

Otolaryngology Department, Unit Otology, Auditory implants and Skull base surgery

Bâtiment Castaigne

Groupe hospitalier Pitié Salpêtrière

47-83 boulevard de l'Hôpital 75651 cedex Paris

Email: yann.nguyen@inserm.fr

word count: 2400

References : 28

Number of figures : 6

Abstract

Introduction: Otosclerosis surgery functional outcomes and complications rely upon the

surgeon experience. Thus, teaching the procedure to the resident to get them over the learning

curve as fast as possible is challenging. Artificial 3D printed temporal bones are replacing

cadaver specimens in many institutions to learn mastoidectomy but are not adapted to middle

ear surgery training. The goal of this work was to adapt such an artificial temporal bone to

comply for otosclerosis surgery teaching and to evaluate this tool.

Material and method: We have modified a commercially available 3D printed temporal bone

by replacing the incus and the stapes of the model by in-house 3D printed ossicles. The incus

could be attached to a 6-axis force sensor. The stapes footplate was fenestrated and attached

on a 1-axis force sensor. Six junior surgeons (resident) and seven senior surgeons (fellows or

consultants) were enrolled to perform a piston prosthesis placement and crimping as done

during otosclerosis surgery. Time required achieving the tasks, and forces applied on the

incus and the stapes were collected and analysed.

Results: No difference between the junior and the senior group was observed for time to

achieve the tasks and forces applied on the incus during prosthesis crimping and placement.

Lower efforts were applied by the senior surgeons in comparison with the junior surgeons

during prosthesis placement (junior vs senior group, 328±202.9 mN vs 80±99.6 mN p=0.008)

and during prosthesis crimping (junior vs senior group, 565±233 mN vs 66±48.6 mN p=0.02).

Conclusion: We have described a new teaching tool for otosclerosis surgery based on the

modification of a 3D printed temporal bone in order to implement force sensors on the incus

and stapes. This tool could be used as a training tool in order to help the residents to self-

evaluate their progression with objective measurements recording.

Introduction

Otosclerosis is a metabolic bone disease leading to bone dystrophy and involving the otic

capsule and ossicles. It will result in a stapes fixation and a conductive hearing loss in an early

stage and inner ear lesions in a later stage resulting in a mixed hearing loss.

Hearing rehabilitation can be performed either by hearing aids or surgical replacement of

the stapes function. The surgical treatment consists of the stapes superstructure resection, the

fenestration or the removal of the stapes footplate, and the placement and crimping of an

ossicular prosthesis between the incus and the fenestrated stapes to restore the conductive

properties of the middle ear. The procedure is very challenging as it is performed through a

narrow field exposure with a speculum placed in the outer ear canal and involves millimetric

and light fragile structures represented by the ossicular chain. When performed by

experienced surgeons, the technique yields excellent result, with hearing improvement and a

postoperative air-bone gap of less than 10 dB in 90% of cases. The most fearful complication

is sensorineural hearing loss than be partial or total and irreversible. Functional result and

complication occurrence may vary with the surgeon experience (1,2). In order to raise the

success rate and diminish incidence of complications among less experienced surgeons,

technical modification have been progressively adopted in the last three decades.

Stapedotomy instead of stapedectomy was proposed to lower sensorineural hearing loss (3).

Laser was used alone (4) or in combination with microdrill (5) to assist the footplate

fenestration and lower the risk of footplate fracture. Nitinol prostheses have been developed

to avoid manual crimping of the prosthesis around the long process of the incus. Other authors

have proposed the use of a robot-based assistance to increase the safety of the surgery(6).

Nevertheless, no tool or technique will be as valuable as the training and the skills and

experience of the surgeon to guarantee the success of the surgery.

Most otologist have been trained trough an apprenticeship in the operating room with the

traditional adage “see one, do one, teach one” known as the Halstedian method (7). This

clinical training can be completed with temporal bone dissection course or free practice in a

temporal bone laboratory (8). However, access to cadaver specimens varies from a faculty to

another and even more from one country to another. Changes on legislation on body donation

(9), medical restrictions due to risk of prions diseases (10) and high costs have further reduced

the access of resident to temporal bone in many training programs. Because of these

restrictions, innovative teaching methods such as artificial simulator such as 3D printed

temporal bones (11), animal models such as sheep (12) or pig or virtual simulators (13) are

employed to reduce the use of temporal bone specimen and shorten the learning curve. 3D

printed temporal bones offer a realistic anatomical representation that can reproduce real case

anatomy based on DICOM images acquired with a CT-Scan. Artificial bones are very

beneficial to learn posterior cavity drilling but are less valuable to teach middle ear cleft

surgery as the ossicular chain is fixed and sometimes poorly reproduced. In the present work,

we will described how we have modified a commercially available 3-D printed artificial

temporal bone in order to provide objective measures to the learner in order to raise his

interest into an extended training for otosclerosis prostheses placement and crimping on such

an artificial simulator.

Material and Methods

Population

Thirteen surgeons were enrolled in the study. All of them were right-handed. Population was

divided into two categories depending on their otological experience. A junior group was

represented by six residents (two women and four men) and a senior group was represented

by six fellows and a consultant from our ENT department (three women, four men).

Modification of the artificial temporal bone

A commercially available 3-D printed temporal bone (Schmidt model, left ear, Phacon,

Leipzig, Germany) (14) was modified to include measurements of force applied on the incus

and the stapes. Malleus and stapes were removed from the commercial device. An access was

drilled superiorly to expose the epitympanum and anteriorly to expose the oval window from

an inner ear point of view. These two accesses allowed to place a modified incus (Figure 1A)

and stapes 3-D printed model obtained from a ossicular chain segmentation reported in a

previous work (15). Ablation of the superstructures and a 500 µm fenestration was performed

with a microdrill to obtain a perforated footplate (Figure 1B). The remaining footplate was

mounted on 1-axis force sensor (range: 0-1N, resolution: 10 mN, Millinewton force sensor,

EPFL, Lausanne, Switzerland, Fig 2) and the incus was mounted on a 6-axis force sensor

(ATI Nano 17, calibration type SI-12-0.12, resolution: 3 mN, Apex, NC, USA fig 3). Sensor

data was recorded in real-time via the same analog to digital interface card (NI 6210, National

Instruments, Austin, TX, USA) and in-house software. Only Components Dx,Dy,Dz provided

by the 6-axis forces sensors, were averaged to obtain the norm of the force applied on the

incus.

Experimental set-up

Participants were asked to place the prosthesis into the fenestrated footplate and around the

long process of the incus under microscopic view (Kaps, Asslar, Germany) in a transcanal

approach through a 5 mm diameter ear speculum. A picture of the simulated surgical

exposure in represented on Figure 4. The prosthesis used was a titanium K-Piston with a 4.5

mm length and 0.4 mm shaft diameter (Kurtz, Dusslingen, Germany). A Hartman alligator

micro forceps was used to place the piston into the stapedotomy and around the incus, and a

Mc Gee wire crimping micro forceps was used to crimp the piston. The prosthesis placement

and crimping was assessed by an external evaluator. After each trial, the prosthesis was

removed, visually inspected and eventually replaced by new one if damaged.

Analysis

The first completed gesture by the participant including prosthesis placement and crimping

would be analyzed. Duration to achieve these two steps was also collected. Considering the

forces measurements, we investigated the shape of the curve corresponding to the force versus

the time during the two steps of the procedure. The peak of force applied on the incus and the

footplate during the placement of the prostheses on the long process of the incus was

collected. This metric quantifies a potential damage to the ossicular chain or the cochlea if an

excessive force is applied. Results were expressed as mean ± SEM. Data were analyzed and

graphics were generated with R version 3.1.3 (R Core Team, 2013, R, Vienna, Austria). Data

are presented as mean ± standard deviation. We used the Mann-Whitney test to evaluate

significance for duration of the procedure and efforts applied on the stapes and the incus. P

values <0.05 indicated statistical significance.

Results

Duration of the procedure

No difference for the duration of the procedure was observed for prosthesis placement (junior

vs senior group, 26±13 s vs 15±4.5 s p=0.13). No difference for the duration of the procedure

was observed for prosthesis crimping (junior vs senior group, 28±10.5 s vs 20±7.4 s p=0.31).

Efforts applied on the incus

No difference on the efforts applied on the incus was observed during prosthesis placement

(junior vs senior group, 720±203.4 mN vs 338±233.1 mN p=0.07). No difference on the

efforts applied on the incus was observed during prosthesis crimping (junior vs senior group,

433±334.1 vs 182±169.3 mN p=0.11).

Efforts applied on the stapes

Lower efforts were applied by the senior surgeons in comparison with the junior surgeons

during prosthesis placement (junior vs senior group, 328±202.9 mN vs 80±99.6 mN p=0.008).

Lower efforts were applied by the senior surgeons in comparison with the junior surgeons

during prosthesis crimping (junior vs senior group, 565±233 mN vs 66±48.6 mN p=0.02).

The results of duration and forces measurements for prosthesis crimping and crimping are

respectively reported in figure 5 and 6.

Discussion

This study describe a training model based on a modified 3-D temporal bone with

measurements of efforts applied on the incus and the stapes during prosthesis placement and

crimping during a simulated otosclerosis surgery. We have shown that during these steps of

the surgery, surgeons with otological experience would apply fewer forces on the stapes in

comparison to surgeon with short or no otological experience.

Advantages and limits of this simulator

The 3D printed temporal bones generally offer a high fidelity for visual and anatomical

representation. Thus the dimensions, approach and exposure of the surgical field could be

easily reproduced in this simulator by using a commercially available temporal bone. With the

potential of customized printed temporal bone, it would be easy to change the surgical scene

from a left to a right ear or simulate difficult cases for advanced surgeons such as narrow oval

niche with facial nerve overhang or long process of the incus necrosis. Furthermore, the use

of a physical simulator allows the learner to use real tools (microscope, surgical tools, and

prosthesis) in order to get accustomed to the tools available in his operating room. Another

advantage of such a simulator is its versatility to compare the user friendliness of different

techniques (e.g. different type of prosthesis, robot-based versus manual technique…) although

the compliance of the ossicular chain does not reflect human physiology and no prediction on

hearing outcomes can be estimated from a comparison of technique or prosthesis with our

simulator.

Nevertheless, some drawbacks limit the value of this simulator. Its realism for ossicular chain

palpation has not been objectively compared to a real ossicular chain. Furthermore, absolute

forces measurements values cannot be considered in order to compare them with previous

reports on ossicular chain manipulation. Indeed, the incus in our set-up is mounted on a long

rod for attachment with the 6-axis force sensor and this creates a leverage effect that does not

directly reflect the effort applied on the incus. The exact force applied on the incus could not

be calculated from the moment of the force as the angle of the applied force may constantly

vary during the prosthesis placement and crimping. Previous studies have already reported

that experts surgeons would apply less forces during otosclerosis surgery simulation

compared to junior surgeons (16,17). Moreover, some other critical steps of the otosclerosis

surgery like scutum lowering or footplate fenestration were not simulated. Difficult

intraoperative conditions such as bleeding were not reproduced. In addition intraoperative

complications such as incus fracture, incudo-malleolar joint rupture and floating footplate,

could not be reproduced in this simulator. At last, the price of the force sensors and the need

of a computer may hamper a large academic use of this simulator even though it can be used

without deterioration through time.

Other models of otosclerosis training surgery

The estimates learning curve of otosclerosis surgery is between 60 and 80 cases (18) and

complications can occur even after the first successful cases (19). For this reasons, simulators

to train residents have been designed. Some authors have created some simple artificial

surgery boxes to perform training out of the operating room (20-22). A more complex model

reproducing not only otosclerosis but also chronic otitis scenarios was proposed by mills et al

(23). These simulators are low cost and easy to transport but have a limited representation of

the anatomy of the middle bone. Thus, it was proposed by another author to glue the oval

window to reproduce pathological conditions observed in otosclerosis in cadaver models (24).

Another totally different approach is represented by virtual simulator. It has become very

popular for temporal bone drilling teaching (13,25) but more confidential for otosclerosis

surgery training (26). With such simulations, resident could train without restrictions even

with personal computers outside medical faculties. The main drawback of this system is the

poor haptic feedback that is limited by the expensive cost of efficient haptic devices with

multiple degrees of freedom and force-feedback.

Conclusion

We report a new teaching tool for otosclerosis surgery based on the modification of a 3D

printed temporal bone in order to implement force sensors on the incus and stapes to measure

efforts applied on these ossicles. We have observed that senior surgeons would apply a lower

peak force on the stapes during prosthesis manipulation. The best use of this simulator would

be to use it as a training tool in order to help the residents to self-evaluate their progression

with objective measurements recording. This training would raise their confidence on one

hand but also allow them to improve their hand positioning, accuracy and steadiness with

training as reported in other models of middle ear surgery training on the other hand (27,28).

The authors would like to thank Armand Czaplinski for his assistance of the 3D printing of

the modified incus and stapes used in this study.

References

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2. Lial PI, Soares VY, Viana LMet al. Stapedotomy in a residency training program. Int Tinnitus J 2013;18:163-7.

3. Kursten R, Schneider B, Zrunek M. Long-term results after stapedectomy versus stapedotomy. Am J Otol 1994;15:804-6.

4. Perkins RC. Laser stepedotomy for otosclerosis. Laryngoscope 1980;90:228-40. 5. Nguyen Y, Bozorg Grayeli A, Belazzougui Ret al. Diode laser in otosclerosis surgery: first

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Assistance Robot for Middle Ear Surgery. Surg Innov 2011. 7. Kerr B, O'Leary JP. The training of the surgeon: Dr. Halsted's greatest legacy. Am Surg

1999;65:1101-2. 8. Levenson MJ. Methods of teaching stapedectomy. Laryngoscope 1999;109:1731-9. 9. George AP, De R. Review of temporal bone dissection teaching: how it was, is and will be. J

Laryngol Otol 2010;124:119-25. 10. Scott A, De R, Sadek SAet al. Temporal bone dissection: a possible route for prion

transmission? J Laryngol Otol 2001;115:374-5. 11. Bakhos D, Velut S, Robier Aet al. Three-dimensional modeling of the temporal bone for

surgical training. Otol Neurotol 2010;31:328-34. 12. Cordero A, Benitez S, Reyes Pet al. Ovine ear model for fully endoscopic stapedectomy

training. Eur Arch Otorhinolaryngol 2015;272:2167-74. 13. Sorensen MS, Mosegaard J, Trier P. The visible ear simulator: a public PC application for

GPU-accelerated haptic 3D simulation of ear surgery based on the visible ear data. Otol Neurotol 2009;30:484-7.

14. Roosli C, Sim JH, Mockel Het al. An artificial temporal bone as a training tool for cochlear implantation. Otol Neurotol 2013;34:1048-51.

15. Kazmitcheff G, Miroir M, Nguyen Yet al. Validation method of a middle ear mechanical model to develop a surgical simulator. Audiol Neurootol 2014;19:73-84.

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18. Yung MW, Oates J, Vowler SL. The learning curve in stapes surgery and its implication to training. Laryngoscope 2006;116:67-71.

19. Sergi B, Paludetti G. Can the learning curve in stapes surgery predict future functional outcome? Acta Otorhinolaryngol Ital 2016;36:135-8.

20. Mathews SB, Hetzler DG, Hilsinger RL, Jr. Incus and stapes footplate simulator. Laryngoscope 1997;107:1614-6.

21. Monfared A, Mitteramskogler G, Gruber Set al. High-fidelity, inexpensive surgical middle ear simulator. Otol Neurotol 2012;33:1573-7.

22. Owa AO, Gbejuade HO, Giddings C. A middle-ear simulator for practicing prosthesis placement for otosclerosis surgery using ward-based materials. J Laryngol Otol 2003;117:490-2.

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Figures legend

Figure 1: Modified incus and stapes

Modified incus and stapes were modified into to be attached to force sensors. The incus was

printed jointly with a rod to ease attachment to a 6-axis force sensor. A stapes foot plate was

printed and then drilled with a 500 µm fenestration. The stapes could then be attached to a 1-

axis force sensor.

Figure 2: Internal view or the modified artificial temporal bone

A commercially available 3-D printed temporal bone (Schmidt model, left ear, Phacon,

Leipzig, Germany) was modified to include measurements of force applied on the incus and

the stapes. An access was drilled to the vestibule to expose the oval window niche from the

inner ear side. The stapes from the commercial temporal bone was removed and replaced by

an in-house 3D printed stapes. This stapes model was mounted on a 1-axis force sensor

(Millinewton force sensor, EPFL, Lausanne, Switzerland). This sensor allowed measurements

of forces applied on the stapes

Figure 3: External view or the modified artificial temporal bone

A commercially available 3-D printed temporal bone (Schmidt model, left ear, Phacon,

Leipzig, Germany) was modified to include measurements of force applied on the incus and

the stapes. Access was drilled from the tegmen to the epitympanum and the incus from the

commercial artificial temporal bone was removed. It was replaced by an in-house incus 3D

printed jointly with a rod that could be attached to a 6-axis force sensor (ATI Nano 17, Apex,

NC). This sensor allowed measurements of forces applied on the incus.

Figure 4: Middle ear cleft exposure through the external auditory canal

The use of an artificial temporal bone (Schmidt model, left ear, Phacon, Leipzig, Germany)

allowed reproducing the surgical and anatomical environment with a high fidelity. The incus

of this model was replaced by an in-house 3D printed incus in order to attach it on a force

sensor. This photo shows the implementation of our incus model into the commercial artificial

temporal bone.

Figure 5: Collected metrics for evaluation of the prosthesis placement in an otosclerosis

surgery model

Six junior surgeons (resident) and seven senior surgeons (fellows or consultants) were

enrolled to perform a piston prosthesis placement in our modified temporal bone model.

Duration of the task and forces collected via two force sensors and applied on the incus and

stapes were investigated. No difference between the groups was observed for duration of the

task and forces applied on the incus. Lower efforts on the stapes were applied by the senior

surgeons in comparison with the junior surgeons during prosthesis placement (junior vs senior

group, 328±202.9 mN vs 80±99.6 mN p=0.008).

Figure 6: Collected metrics for evaluation of the prosthesis crimping in an otosclerosis

surgery model

Six junior surgeons (resident) and seven senior surgeons (fellows or consultants) were

enrolled to perform a piston prosthesis crimping in our modified temporal bone model.

Duration of the task and forces collected via two force sensors and applied on the incus and

stapes were investigated. No difference between the groups was observed for duration of the

task and forces applied on the incus. Lower efforts on the stapes were applied by the senior

surgeons in comparison with the junior surgeons during prosthesis crimping (junior vs senior

group, 565±233 mN vs 66±48.6 mN p=0.02).

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6