Virtual Reality in the Operating Room

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14 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

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3981
S U L Z E R T E C H N I C A L R E V I E W 1/2 0 0 1
17

Worldwidemorethan 600000
knee joints are replaced
annually by an artificial one. In a
conventional orthopedic proce-
dure, success depends largely on
the skill and the feel of the sur-
geon, whose view often is obstruct-
ed by blood or tissue. Even though
most orthopedic surgery has be-
come routine, the risk of incorrect-
ly placed implants still exists. Clin-
ical studies show that wrongly
positioned knee prostheses have a
shortened functional life. Comput-
er assistance now enables the sur-
geon to follow the operational steps
in virtual space on a color-screen,
allowing him or her to navigate the
instruments with higher accuracy
(Fig. 1

and box).
CREATING A 3D MODEL
OF THE ANATOMY
Sulzer Medica’s Navitrack system
uses data from computed tomogra-
phy (CT) or magnetic resonance
imaging (MRI) to create a three-
dimensional model of the patient’s
anatomy, which, together with a
model of the instruments and
implants required for the opera-
tion, is stored on hard disc (Fig.2

).
CT scans are used to register bone
structures, while MRI creates also
models of softtissue structures and
is used for cruciate ligament opera-
tions. Typically, the resolution of
the 3D model is limited by the slice
thickness of the tomography,
which is about 1 mm, and the
pixel-size of the scan of 0.4mm.
Before starting the surgery, the
surgeon matches points of refer-
ence on the patient’s bones with
the virtual 3D model displayed on
the monitor. By this calibration,
the virtual model is aligned with
the real body structure. Attached
on the instruments are trackers
and sensors that allow real-time
navigation (Fig.3

). Every move-
ment that the surgeon performs
with a real instrument during the
operation is transmitted to the
workstation by a spatial meas-
urement system. With the model of
the patient and the tools displayed
on the monitor in real time, the
surgeon can follow all movements
in the virtual space without any
restrictions of sight; patient move-
Virtual Reality in the
Operating Room
The Navitrack™ system for
computer-assisted surgery
from Sulzer Medica extends
its fields of application.
Besides spinal surgeries,
the system can be used in
total hip and knee replace-
ment, as well as in anterior
cruciate ligament operations.
In August 2000, the system
received clearance from
the US Food and Drug
Administration.
HANS RUDOLF SÄGESSER
SULZER MEDICA
1

In virtual
reality, the
human body can
be seen in a way
that would never
be possible in
reality.
3981
18
S U L Z E R T E C H N I C A L R E V I E W 1/2 0 0 1
ment is compensated for as well.
These features eliminate the need
for intraoperative control X-rays,
thus saving time in the operating
room.
NAVITRACK IMPROVES
ACCURACY
Astudy carried out at the Charité
Hospital in Berlin (DE) from 1994
to 1997 found improved accuracy of
the placement of pedicle screws in
spinal surgery (Fig.4

). Misplaced
screws increase the risk of struc-
tural loading, inadequate fixation
or even nerve damage. According
to the study, the use of Navitrack
reduces the number of required re-
operations and potential long-term
deficits, hence minimizing costs
both for the patient and for the
medical care system.
Navitrack can be equipped with
either optical or electromagnetic
(EM) tracking systems. While
enhancing the procedure, Navi-
track’s impacts on the current
operating techniques are very lim-
ited. As the magnetic sensors in
the EM systems are sensitive to
ferrous materials present in the
operating fields, the use of non-fer-
rous tools is required. Obviously,
while using the optical tracking
system where a camera registers
the movement of the tools, certain
line-of-sight restrictions have to be
accepted. Preoperatively the to-
mography and the calibration have
to be done for each surgery.
CT scan (or MRI)
Data transfer
3D modeling
Navigation
Anatomical registration
Tools’ calibration
3

Atracker attached to the instrument together
with a spatial measurement system determine
the position of the instrument during a surgery,
in this case during a total hip replacement.
(Photos: Waldkrankenhaus Rudolf-Elle,
Eisenberg, DE)
VIRTUAL REALITY:
A BETTER IMAGE OF REALITY
“Virtual Reality” has become a slogan for a wide range of technical
applications where modern imaging technology helps to visualize
and understand processes not easily captured without the aid of
computers: Architects walk through houses before they are being
built, engineers get an insight of the interior of an automotive
engine, and surgeons can navigate their instruments precisely.
All this happens with the help of modern computers rather than in
the real world. The main features of computer systems utilizing
virtual reality are visualization of the objects of interest and
precise simulation of actions in real time or even in advance.
Sulzer Medica’s Navitrack system is essentially different from
intraoperative X-rays of both the patient’s anatomy and the
surgical instruments watched real-time on a monitor.
2

Steps in the Navitrack image-guided surgical
process: from image acquisition it takes 30 minutes
to precise navigation in the operating room.
S U L Z E R T E C H N I C A L R E V I E W 1/2 0 0 1
19
Food and Drug Administration,
which makes Navitrack the first
computer-aided surgery product to
be approved for various applica-
tions in orthopedic surgery. The
system is now available in the USA
and Europe for use in total hip and
knee replacement, cruciate liga-
ment operations (anterior and pos-
terior; Fig.5

) as well as for spinal
surgery. A wide field for future
applications is minimally invasive
surgical (MIS) techniques. The use
of image-guided systems will
broaden the view of the surgeon
performing MIS from the narrow
end of the endoscope to the full
3D-visualization of the patient’s
anatomical structures on the
screen.Ω
ROBOTS VS. NAVIGATION
SYSTEMS
Today robots are used in orthope-
dic surgery to perform precise
reaming of the femoral cavity to
achieve better primary stability of
femoral stems. Here the robot com-
pletely takes over the work from
the surgeon. Navigation systems
like Navitrack are passive and
merely support the surgeon per-
forming the operation. Based on
the supplied information, e.g. hid-
den bone structures or the pro-
posed size of an implant, the sur-
geon performs the next steps,
while always keeping complete
control of the surgical process. In
this sense the Navitrack system is
the bridge between specific surgi-
cal requirements and integrated
state-of-the-art computer technol-
ogy.
Navitrack, developed by Orthosoft
Inc. in Montreal (CA) and distrib-
uted exclusively by Sulzer Medica,
has been used successfully in
Europe since 1997, with more than
500 patients for the implantation
of pedicle screws. In August 2000
it received clearance from the US
F O R MO R E D E T A I L S
Sulzer Orthopedics Ltd
Hans Rudolf Sägesser
Postfach
CH-6341 Baar
Switzerland
Telephone +41 (0)41-768 33 92
Fax +41 (0)41-768 13 92
E-mail rudolf.saegesser@sulzer.com
4

With Navitrack the surgeons can
follow all movements of the surgical
instruments in a virtual model of the
patient’s bone structure. Astudy
showed that Navitrack improves the
accuracy of spinal surgery.
5

Navitrack extends its field of application. In addition to
classical surgeries like the replacement of a cruciate ligament,
future applications are minimally invasive surgical techniques.