Surgeon's comfort: The ergonomics of a robotic exoscope using a
, Matthias Demetz
, Aleksandrs Krigers
, Marlies Bauer
, Sara Lener
, Johannes Kerschbaumer
, Sebastian Hartmann
, Helga Fritsch
, Christian F. Freyschlag
Department of Neurosurgery, Medical University of Innsbruck, Anichstr. 35, 6020, Innsbruck, Austria
Division of Clinical and Functional Anatomy, Medical University of Innsbruck, Müllerstr. 59, 6020, Innsbruck, Austria
Introduction: Conventional microscopes have certain limitations in terms of posture and ergonomics. Monitor-
based exoscopes could solve this problem and thereby lead to less work-related sick leave for surgeons.
Research question: The aim of this study was to assess the ergonomics, usability, and neurosurgeon's comfort of a
novel three-dimensional head-mounted display-based exoscope in a standardized setting.
Material &Methods: 34 neurosurgeons participated in a workshop on the exoscope, which features a head-
mounted display and a head gesture-triggered control panel. After completion of a custom-made 10-step
microsurgical exercise, image quality and comfort were assessed using a questionnaire. The participants'
posture during the exercise was analyzed using a video motion analysis software.
Results: 34 participants (median neurosurgical experience: 6 years) were included. The median time to complete
the exercise was 12 min [IqR 9.4, 15.0]. Younger participants (p ¼0.005) and those with video game experience
(p ¼0.03) had a signiﬁcantly steeper learning curve. The median overall satisfaction was at 80% in general and
82% for image quality. The median upper body as well as the median head coronal displacement from the neutral
axis were 0. Participants with less microsurgical experience showed less head/body displacement during the
exercise (p ¼0.01).
Discussion and conclusion: Using the microsurgical training tool, we were able to depict a steep learning curve with
a sufﬁcient learnability of the most relevant commands. The exoscope excelled in usability, image quality as well
as in ergonomic and favorable posture and could thus become an alternative to conventional microscopes due to
the potentially elevated surgeons' comfort.
Since the ﬁrst use of the microscope for a neurosurgical procedure,
surgeons and industry were striving to evolve this tool towards being the
essential piece of neurosurgical equipment to date (Uluç et al., 2009).
Despite tremendous technical advances, modern microscopes still
comprise disadvantages, such as limited mobility and angulation, the
need to operate the microscope through switches (footswitch, mouth-
piece, handlebar) but additionally physical discomfort experienced by
neurosurgeons due to potentially unergonomic postures (Figueiredo
et al., 2020;Weinstock et al., 2021;Helayel et al., 2021). The discomfort
during surgical interventions and its impact on the long-term working
ability has gained importance in the past decades, especially due to the
increment of surgical complexity and duration (Siller et al., 2020). Pre-
vious studies have already demonstrated an increased risk of
work-related musculoskeletal disorders (WMSDs) and degenerative spi-
nal deformities for surgeons performing microsurgical procedures (Lav
et al., 2020;Auerbach et al., 2011). Especially spine surgeons are at risk
of WMSDs by working for hours in non-neutral positions, with ﬂexion of
the neck and coronal malalignment as they perform microscopic sur-
geries in a standing position, frequently leaning over the operating ﬁeld
(Park et al., 2012). Improving these shortcomings may lead to a reduced
number of days absent due to sick leave and a higher long-term working
ability for surgeons (Oertel and Burkhardt, 2017;Roethe et al., 2020;
Mamelak et al., 2010).
* Corresponding author. Department of Neurosurgery Medical University of Innsbruck, Anichstraße 35, A-6020, Innsbruck, Austria.
E-mail address: email@example.com (C.F. Freyschlag).
denotes Co-First Authorship.
Contents lists available at ScienceDirect
Brain and Spine
journal homepage: www.journals.elsevier.com/brain-and-spine
Received 28 October 2021; Received in revised form 13 December 2021; Accepted 16 December 2021
Available online 28 December 2021
2772-5294/©2021 The Authors. Published by Elsevier B.V. on behalf of EUROSPINE, the Spine Society of Europe, EANS, the European Association of Neurosurgical
Societies. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Brain and Spine 2 (2022) 100855
In recent years, exoscopes have gathered advantages compared to the
conventional surgical microscope. Not only a more comfortable posture
for the surgeon, but also the technical prospects of fully digitalized image
processing and robot movement have been included. In contrast to pre-
vious microscopes, exoscopes do not project the image into ﬁxed eye-
pieces, but onto external mobile screens (Amoo et al., 2021).
Nevertheless, due to the distance between the surgeon and the monitor,
exoscopes still harbor limitations regarding the depth of the visual ﬁeld
and the visual quality at higher magniﬁcation (Ricciardi et al., 2019;
Herlan et al., 2019;Gonen et al., 2017).
The RoboticScope (RS; BHS Technologies GmbH, Innsbruck, Austria)
was designed to overcome this issue by projecting the images on external
displays directly in front of the eyes, comparable to virtual reality (VR)
goggles. The RS consists of a head unit containing 2 video cameras
mounted onto a 6-axes robotic arm. The image is displayed to the surgeon
via two digital micro-displays (Head-mounted display, HMD) that pro-
vide a three-dimensional image of the surgical ﬁeld in real time (Fig. 1).
Another major advantage is the hands-free control of the robotic arm that
has been implemented and uses head gestures on a virtual interface
(Fig. 1). A foot pedal serves as a safety measure against uncontrolled
movements of the RS by only reacting to head gestures when the pedal is
pressed. General head movements (for example to achieve a comfortable
posture for the surgeon without moving the robotic arm) do not change
the camera position, if the foot pedal is not pressed. The RS has already
been successfully tested on cadavers and in the clinical setting, where
especially hands-free control and visualization quality were reported as
major advantages (Sch€
ar et al., 2021).
The aim of this study was to investigate the ergonomics, usability and
neurosurgeon's comfort of the novel three-dimensional head-mounted
display (HMD)-based exoscope in a standardized setting.
2. Material &methods
2.1. Inclusion of study participants
Neurosurgeons of different levels of qualiﬁcation (n ¼34; 15 senior
consultants, 2 consultants, 12 residents, 5 interns; 21 men, 13 women)
from the authors' department participated in a workshop including a
demonstration of the exoscope as well as skill training using a stan-
dardized microsurgical training tool. Participants were not previously
trained on the device and signed a written informed consent form for the
use of their data and video footage in pseudonymous form. Prior to
enrollment, each participant was assigned a study ID, which was docu-
mented on the paper- and electronic-based case report forms (CRFs) as
well as the video recording screen.
2.2. Pre-interventional training
Stereoscopic vision was tested using a commercially available stan-
dardized stereoscopic vision assessment tool (Stereo Fly test, Stereo
Optical Company Inc., Chicago, IL, USA). Each participant received a
personal 30-min user instruction performed by the staff of BHS Tech-
nologies GmbH prior to conduction of the microsurgical skills assess-
ment. The participant's interpupillary distance and visual impairments
(shortsightedness, farsightedness) were compensated at the HMD by
means of dioptric compensation. Following the instruction, the partici-
pants received the HMD to test the commands with technical assistance.
Participants were instructed on how to use the foot pedal as well as the
HMD to execute the most important commands (Step 1: press the foot
pedal, Step 2: Choose the command at the user interface by pointing the
cursor with head movement Step 3: Leave the foot pedal to activate the
command). The execution of each training step had to be ticked in an
electronic CRF to allow for a standardized pre-interventional training.
2.2.1. Customized microsurgical training tool assessment
A custom-made microsurgical training tool was designed by one of
the authors (AA) in order to perform a quantitative analysis of the exo-
scope usability. The microsurgical tool contained ten eyelets set at
different angles, thereby forcing participants to use different head
gesture commands with the HMD, respectively. The training tool consists
of a base plate made of Ethylene vinyl acetate (EVA) and ten metal pins
which were pierced through the ground plate. Prior to afﬁxing small
eyelets (inner diameter: 1 mm), the metal pins were bent using needle-
nose pliers to create different angles. A paint marking of the beads as
well as a number marking on the base plate served to guide the direction
WMSDs work-related musculoskeletal disorders
HMD head-mounted display
EVA Ethylene vinyl acetate
Fig. 1. Start position of the participant with HMD set up and exercise centered on the working table (A). Operating the robot controlled exoscope with the user
interface (B, 1 ¼orbit movement, 2 ¼magniﬁcation, 3 ¼translating movement, 4 ¼focus).
A. Abramovic et al. Brain and Spine 2 (2022) 100855
of the course.
Participants were asked to perform this exercise using microsurgical
instruments (needle holder, forceps) and a 6/0 nylon suture. The stan-
dardized course of the exercise consisted of centering and aligning each
eyelet using the tilting option of the RS, followed by threading the needle
through the eyelet with the help of a needle holder and/or forceps. Prior
to passing the needle, each eyelet had to be centered, so that the hole was
no longer visible due to the perpendicular view (Fig. 2). The same steps
had to be applied for each eyelet, thereby provoking various exoscope
positions. The working distance as well as the starting position were
standardized to provide consistent data. In case of a technical problem,
such as slipping of the HMD, technical assistance by the manufacturer
2.2.2. Participant questionnaire
Following the execution of the training exercise, participants were
asked to ﬁll out an electronic 28-item questionnaire including 5-point
Likert scales and text answers. In addition to basic data of each partici-
pant (e.g., age, gender, right/left-handed, neurosurgical experience), the
survey consisted of questions regarding previous experiences with
various virtual reality (VR), video games as well as usability and comfort
using the novel exoscope.
2.2.3. Video analysis
The video analysis system of the training exercise consisted of ﬁve
cameras recording different angles of the exercise itself, as well as the
participant- and exoscope movements (Fig. 3). The front side camera as
well as the exoscope video recording were used to monitor the centering
and angulation process of every single eyelet throughout the exercise,
moreover, possible operating errors by participants were documented as
well. The quantitative analysis of correctly centered eyelets was evalu-
ated with a custom-made "Bullseye-Score" (Fig. 4). The qualitative video
analysis was performed by all authors, including documentation of time
required for performing the whole exercise, time per eyelet, operating
errors, commands per exercise and commands per eyelet using a custom-
One video camera was placed exactly behind the participant in order
to provide accurate video footage for the quantitative 2D-video motion
analysis performed by appropriate software (Kinovea, v. 0.9.3). Stan-
dardized coronal angle measurement was performed for the upper body
as well as the head movement (Fig. 5). The video analysis was performed
by two of the authors (MD, AA) following a standardized video analysis
protocol. Operating errors were deﬁned as commands for the RS that
were either not executed due to incorrect handling (i.e. foot pedal not
pressed) or were immediately corrected by the participant (i.e. wrong
command chosen). Angular movements from the starting position (angle
per second; /s) were measured and documented in a Windows Excel
sheet (Microsoft Ofﬁce, Version 1908, Microsoft, Inc., Redmond, WA,
USA). The angulation limit was deﬁned at reaching a maximum excur-
sion of the RS, from where repositioning or readjustment became
2.2.4. Statistical analysis
Statistical analysis was performed using IBM SPSS (IBM SPSS Statis-
tics, version 24.0, IBM Corporation, NY, USA). Data normal distribution
was checked by histograms and Kolmogorov-Smirnov-test. Mann-Whit-
ney-U-test, Wilcoxon rank sum test, Chi (Figueiredo et al., 2020) test or
Spearman's rank correlation coefﬁcient test were used to detect signiﬁ-
cant similarities or differences. A p-value of 0.05 was considered sta-
The authors' theory was that due to the hands-free HMD the posture
and ergonomics of neurosurgeons could be improved and thus the RS
could become an alternative to conventional microscopes. However, it
had to be determined using a standardized procedure whether the us-
ability of this novel exoscope can be learned quickly and how the par-
ticipants' satisfaction with, for example, depth of ﬁeld and resolution is.
34 participants (21 men, 13 women; mean age: 35 9 years) were
included. The median neurosurgical experience amounted to 6 1.4
years. 62% of the participants had experience with videogames and 9%
had already used virtual reality (VR) headsets.
3.1. Microscopic training exercise
The median time needed by participants to complete the exercise was
12 min (inter-quartile range [IqR] 9.4, 15.0) with signiﬁcantly less time
needed for eyelet 7–10 compared to eyelet 2–5, especially in younger
participants (p ¼0.005, r ¼0.49), further the participants with video
game experience showed signiﬁcantly less time to complete the entire
exercise (p ¼0.05). The median Bulls-Eye score amounted to 27/30 (IqR
24; 28). The median number of commands to ﬁnish the entire exercise
was 38.5 (IqR 28.3, 42.8). The median number of operating errors was
3.5 (IqR 1.0, 7.0). 12.5% (4/28) of the participants needed technical
assistance during the conduction of the exercise. In the median, the
angulation limit of the RS was reached 2 times per participant (IqR 1.0,
3.2. Surgeon's questionnaire
In general, the participants had no major difﬁculties using the RS, the
median overall satisfaction was at 80%. There was no signiﬁcant differ-
ence between younger and more experienced surgeons with regard to
technical difﬁculties except that younger participants had less difﬁculties
with the user interface and the HMD commands of the RS (p ¼0.014).
Overall satisfaction with the image quality of the RS was 82%, this
correlated signiﬁcantly with the preference to use the device more often
during surgery (p ¼0.001) as well as feeling conﬁdent using the RS in by
themselves (p ¼0.004). A majority of 88% of the participants reported to
feel safe enough to use the RS in the OR with technical assistance.
Fig. 2. Standardized microsurgical test with eyelets shown from different perspectives. Participants were asked to perform the exercise in a standardized fashion for
each eyelet (Step 1: Centering of the eyelet, Step 2: Tilting the exoscope until the hole of the eyelet was not visible, Step 3: Threading the 6/0 needle through the hole).
A. Abramovic et al. Brain and Spine 2 (2022) 100855
3.3. Quantitative 2D-video motion analysis
The majority of participants showed minor median displacement of
the upper body from the neutral axis (Fig. 5) with 0[IqR 3, 5], the
median head accounted for 0[IqR 0, 2]. The statistical analysis revealed
a signiﬁcant correlation of low head/body displacement and less time (p
¼0.019) for the conduction of the exercise. The more experienced par-
ticipants showed signiﬁcant more head tilt starting at 20(p ¼0.01, r ¼
0.48) and the inﬂuence on movement of the RS was signiﬁcant starting at
25of tilt (p ¼0.035, r ¼0.42). Participants with less body shift also
reported of signiﬁcant less difﬁculties for the operation of the RS (starting
at body tilt >10,p¼0.038, r ¼0.43). A higher degree of head/body
shift was signiﬁcantly associated with a reduced number of head repo-
sitioning while performing a single command, such as tilting the RS
(starting at head tilt >25,p¼0.035, r ¼0.44).
The aim of this study was to investigate usability, ergonomics and
neurosurgeon's comfort of the novel three-dimensional HMD-based
exoscope. We demonstrated that a robot-controlled exoscope with head-
mounted displays and gesture controls can be used comfortably for
microsurgery and that introduction and exercise are not time consuming
in comparison to a classical operating microscope. Despite the constant
development of new technologies, the basic design of the surgical mi-
croscope with eyepieces is widely used and has remained close to its
original development. Due to the unergonomic position that microsur-
gery often requires, long-term health of surgeons as well as the optimal
surgical outcomes for patients are at higher risk. A recent questionnaire
has shown reduced concentration and surgical speed in roughly 20% of
microsurgeons, due to long-term procedures using conventional micro-
scopes (Howarth et al., 2018). About 8% of the surgeons experienced
increased tremor due to the discomfort and 29% received medical
treatment due to WMSDs (Howarth et al., 2018). The use of a HMD al-
lows a rather neutral head position to gain a more comfortable posture
for the surgeon notwithstanding the camera position.
During the conduction of this study, the participants reported an
intuitive handling of the RS supported by the simple user interface. As a
Fig. 3. Workﬂow diagram showing the position of the exoscope (RS) as well as the different camera positions and the corresponding video angles (a–d).
Fig. 4. Bullseye score. Each eyelet was assessed respectively, thereby creating a score reaching from 10 (minimal centering of each eyelet) to 30 (optimal centering of
A. Abramovic et al. Brain and Spine 2 (2022) 100855
consequence, the majority of the participants would continue to use the
RS in the operating room. The desire for technical assistance can be
explained with the novelty of the device and the high quality standards of
neurosurgeons. Due to the lack of experience with using the RS, some
participants reported dizziness and discomfort while using the HMD. This
may be due to the unusual weight of the HMD (approximately 500 g) as
well as the cable, which connects the HMD to the RS. During the study,
the technical assistance primarily served to optimize the visual quality
and the appropriate positioning of the HMD. Nevertheless, this ﬁnding is
contrary to previous studies, reporting only 58.9% of the surgeons
willing to use monitor-based exoscopes in the OR (R€
osler et al., 2021).
The pre-interventional assisted training of 30 min was sufﬁcient enough
to minimize the median number of operating errors to only two, hence a
safe transition of this technique into the operating room could be per-
formed with minimal effort. The image quality as a fundamental
parameter in microsurgical operations was reported with a median of
82% overall satisfaction. An optimal adjustment of the HMD even prior to
the start of the exercise is key to achieve high satisfaction with the visual
quality. On the contrary, users reported that HMD needed to be reposi-
tioned during the course of the exercise due to misaligned position of the
displays, which could cause dizziness and even nausea. The weight of the
HMD should also decrease over time as these inputs may serve as an
impulse for a future improvement of the RS and HMD. The user friend-
liness of the RS interface as well as the possibility to train the relevant
commands using a simple microsurgical tool offers excellent conditions
for a safe and swift transition towards the exoscope.
Although we discovered a steep learning curve in the majority of the
study participants, there was a signiﬁcant higher efﬁciency in partici-
pants with previous video game exposure and/or low microsurgical
experience. Consequently, participants with video game experience
described the RS as even easier to use than those without video game
experience. This group also performed signiﬁcantly better with regard to
operating errors and felt more secure than participants with no video
game history or a longer experience using a conventional microscope.
Using the custom-made microsurgical skill training tool, the authors
were able to perform a quantitative assessment of the surgeons' skills
using the RS. The microsurgical training tool has not only shown as an
efﬁcient method for dexterity training but is also an effective method to
train the most important micro- or exoscopic commands which are
needed in the OR. The model used here allows conclusions to be drawn
regarding the learning curve for usability, since a large number of com-
mands and settings were required to switch between eyelets one through
The advantage of head-mounted displays allows a neutral position
during surgery, thereby potentially reducing WMSDs and allowing sur-
geons a more focused and precise handling of the surgical area. The re-
sults of this study showed a median head and body displacement
amounting to 0, meaning the participants stayed in a neutral position
during the majority of the training session. This ﬁnding is in accordance
with previous studies reporting a signiﬁcantly improved surgeons' com-
fort using monitors instead of oculars (Roethe et al., 2020). Neurosur-
gical residents with low microscope experience and interns have shown
even less head/body displacement which underpins the simple applica-
bility of this novel device. Previous studies comparing conventional with
monitor-based microscopes showed a 91.7% preference of the surgeons
for the use of monitor-based models (Eckardt and Paulo, 2016). The risk
for WMSDs is especially high in (micro-)surgical specialties with a
chronic pain incidence of up to 40% (Howarth et al., 2018;Lakhiani
et al., 2018;Yu et al., 2012,2016;Franken et al., 1995;Gorman et al.,
2001;Wong et al., 2014;Mendez et al., 2016). Recent ﬁndings showed a
fourfold increase of weight in case of a 30neck ﬂexion which could
explain the negative impact of chronic microscope usage for the career
durance of microsurgeons (Hansraj, 1016). Display-based exoscopes
could therefore play a major key role in the prevention of WMSD-related
sick leave, especially in surgeons with high operative caseloads.
This study includes several limitations which reduce the validity of
the results. Due to the relatively short duration of the run (12 min), side
effects potentially occurring during surgical procedures lasting for
several hours could not be recorded. This will require further clinical or
cadaver studies. The ability to assess image quality may be reduced in
participants with limited microsurgical experience due to lack of com-
parison with conventional microscopes. The questionnaires were mainly
based on 5-point Likert scales which may not allow a detailed itemization
of the participants' satisfaction with the RS.
The robot-controlled exoscope has shown as a novel approach with
favorable contentment of experienced as well as young neurosurgeons.
Image quality as well as exoscope handling were reported to be sufﬁcient,
thereby providing a safe and easy transition of the RS into the operating
room. The custom-made microsurgical tool proved as an efﬁcient method
for training the relevant commands of the robotic arm. Using the RS, the
participants had a neutral posture, which may lead to less work-related
musculoskeletal disorders in the long-term.
This research did not receive any speciﬁc grant from funding agencies
in the public, commercial, or not-for-proﬁt sectors.
Declaration of competing interest
The authors declare that they have no known competing ﬁnancial
Fig. 5. Analysis of body and head posture during the exercise. The reference
points were set at the uppermost point of the head, the coronal rotational center
of the neck and the right shoulder for head movement. Upper body movement
was measured as the angle between the horizontal, the lumbosacral spine as
well as the coronal rotational center of the neck.
A. Abramovic et al. Brain and Spine 2 (2022) 100855
interests or personal relationships that could have appeared to inﬂuence
the work reported in this paper.
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