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accuracy the desired leg alignment, which was
defined as 180° femoro tibial mechanical angle,
with the femoral and the tibial components
placed respectively to 90° with respect to the
femoral and tibial mechanical axes. This
technology was used at such an early stage, that
users were very anxious, to not say suspicious
of the numbers displayed on the monitor screen,
in spite of extensive laboratory experiments
[35, 36]. However, very limited number of
patients had been done with computer-assisted
navigation at that time and therefore the
outcomes were unknown. This phase was very
stressful and time-consuming because not all
clinical situation had been tested before, so that
conventional instrument was also used to
control any computer recommendations. It took
few years of trial-errors testing before the
system was considered as fully reliable.
Meanwhile, each phase of computer-assisted
navigation technology, i.e. set-up, registration
and planning described above were improved
in the view of facilitating the work of
arthroplasty surgeons. On the other hand, there
was still a great need for improvements for
user-friendliness of the technology compared
to conventional surgery. Most of the studies at
the beginning of 2000 showed that navigation
was clearly time-consuming [about 25% more
than traditional/conventional surgery] and was
also very disruptive, which put off most of the
arthroplasty surgeons from the technique.
Later, a study has confirmed that CT-free
navigation was as good as CT-based navigation
[12], which made the tool more appealing
because there was no need for any pre-operative
medical imaging, which were expensive and
time-consuming. The registration became
slightly easier, slicker and provided reliable
frame of reference on which the surgeon could
navigate the jigs to cut appropriately the distal
femur and the proximal tibia. Numerous
publications including meta-analysis confirmed
statistical improvement of leg alignment,
coronal and sagittal implant positions with the
use of CAS with respect to conventional instru
mentation [37, 38, 39]. However there was still
controversies regarding CAS usefulness on
functional outcomes and long term implant
survivorships [40]. Obviously no one could
answer these relevant questions because the
technique was still to its infancy stage.
However, users could meanwhile analyse the
benefit of this technique on soft tissue
management, which is a known as a key factor
to TKA success.
Soft tissue
management software
The advance of new software enabled the
surgeons to assess flexion and extension gap of
the knee more accurately than before after the
tibial cut resection [41, 42]. Computer assisted
measurements allowing measuring flexion and
extension gaps between the femur and the
resected tibia very accurately.Most importantly,
with such planning feature the surgeon could
plan the full distal femoral cuts before any
actual cuts were even performed [43]. We used
more and more this software in the more
complex cases, such as fixed flexion contracture
valgus knees. Soft-tissue management in these
knees is very challenging. This technology
does provide a very accurate intra-operative
measuring soft tissue envelope tool to fine tune
and tailor soft tissue release during TKA. Some
of my colleagues continued to use the measured
resection technique, while some others used
uniquely the gap management technique.
Personally, I used one or the other depending
on the patient’s case complexity. Clearly this
type of instrument allowed us to improve the
way we assessed the knee and gave us
immediate feedback on the necessary sequential
release that had to be performed to ideally
align and balance the knee. It is striking to see
how different each knee is to the next one and
to observe, as well, how two similar pre-
operative knees (i.e. examination and x-rays)
would react completely differently to stress
measurements using accurate CAS assessment
and guiding. From there, several teams have
developed algorithms to ideally balance the
knees [43, 44, 45].