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Knee Navigation in Knee Arthroplasty in 2014 – 15 years of experience
35
and improve the device [26, 27]. The original
goal of this tool was to reproduce more
consistently the recommended leg alignment
for TKA, which has always been considered as
an important factor for long-term survivor of
knee replacements even if this concept is yet
debated [28, 29].
At the beginning of the 21
st
century, a few
competing navigation systems were out there
and offered to knee arthroplasty surgeons.
Despite the appealing attraction to robotic or
complex CT-based navigation systems, CT-free
navigation systems were preferred and gained
popularity in the orthopaedic community [30,
31]. However, the tools developed at the time
were still rudimentary and sometimes very
primitive in some of the systems, which made
the surgeon’s work more difficult and disruptive
than the use of even complex conventional
instrumentations. Nevertheless, at the end of
this prototypal phase four steps were clearly
identified in any CAS System: Set-up,
Registration, Planning and Execution [32, 33].
The set-up step
is the fundamental step of
fixing markers in the bone to refer any
anatomical landmarks or proceed for any sort
of registration. Several solutions have been
proposed, including pins, K-wires, small drills,
bi-cortical screws, etc, to secure trackers in the
bone that will stay from the beginning until the
end of the surgery [34]. A lot of options given
to surgeons were very cumbersome, sometimes
not reliable, most of the time not user-friendly
at all and most of all were time consuming!
Registration step
is the second step consisting
in collecting anatomical and/or kinematical
landmarks to build a frame of reference straight
from the patient’s anatomy, which were then
used for CT-free navigation. The other
alternative was to use some of these landmarks
to match the pre-operative patient’s CT data to
build an image-guided frame of reference. CT-
free navigation technique did not required any
preoperative CT scan from patients which was
a major advantage with respect to CT-based
navigation. In addition to that, the compulsory
matching process to combine the patient’s
anatomic data to the pre-operative 3-D imaging
reconstruction was a complex mathematical
process, which was still under evaluation.
Planning
is the third step, which was easy to
do and probably the nicest feature with CT-
based navigation. For CT-free navigation, the
planning step was at its very early stage of
evaluation. Later this phase was developed and
implemented very extensively and we will
elaborate on that aspect later. However very
basic planning such as implant sizes was
already available and displayed.
Execution
is finally the last and fourth step
which was done by surgeons using computer
guided conventional instrumentations. It was
clear that the set-up and registration phases
were very disruptive, in comparison to
conventional instrumentation, and changed the
way surgeons performed the surgery. Some of
the systems were more advanced than others
and I was lucky enough to use a system which
allowed us to complete knee replacements
without any major disruption with respect to
conventional surgery from the beginning to the
end of the surgical procedure. The main reason
of that was because the development of the
computer assisted tool was done to follow
conventional instrumentations without trying
to disrupt the usual surgical flow.
The prototypal phase was the phase where
enthusiastic innovators enjoyed to explore the
field. Many things were set at that stage such as
the computer usability in theatre, the use of
infrared technology and the four steps described
above. However the tools were still crude and
the surgeons had to adapt to the machine and
not the opposite. Nonetheless a full TKA could
be performed within reasonable time with good
precision and accuracy.
Measured resection
software
The basic concept on which this system relied
on was the measured resection technique. The
system was developed in order to help the
surgeon to reproduce with high precision and