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: [email protected]
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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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.
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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.
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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