37 / 242
Knee Navigation in Knee Arthroplasty in 2014 – 15 years of experience
37
Refinement of the
technique and
intelligent use of data
collection
After assessing and reviewing at length our
knees during and after computer-assisted
surgery, it became obvious that more work
needed to be done regarding the frame of
reference acquisition in order to improve for
example the femoral or tibial rotations which
were not well defined [46, 47, 48]. Secondly, it
was also evident that the introduction of
accurate intraoperative tool for patient’s
assessment was good but still only identified a
partial view of the “whole picture” of the
patient. For example, intraoperative tool were
assessing non weight bearing knee kinematics
[49, 50, 51, 52, 53]. Thirdly any reconsideration
of the concept of leg alignment or soft-tissue
balancing in knee arthroplasty would require
accurate intra and perioperative measurements
[54, 55].
Our work has been concentrating on assessing
more carefully the anatomical landmarks use
for femoral and tibial component rotation [56,
57, 58]. Few teams around the world had
similar approach. Siston
et al.
reassessed
completely the CT free navigation concept and
analysed the optimal landmarkings to build
reliable and reproducible frame of references
[46, 47, 59]. One of the most remarkable
findings was to show evidence of the
effectiveness of combined landmarks to define
the femoral and tibial rotation. Some others
like Victor
et al.
did tremendous work to
evaluate soft tissue envelop properties using
CAS [60]. We were also keen to use CAS as an
algorithm management tool for soft tissue
management. Other teams had similar
approaches [43, 44, 55].
The second issue was the inadequacy between
intraoperative data, even accurate, and
preoperative condition or postoperative
kinematics. That is the reason why our team,
and others, have worked extensively on the
evaluation and development of non-invasive
CAS that would provide a true picture of
dynamic patient kinematics. Our work proved
that, alignment and tissue envelop laxity
(within 40 degrees) could be recorded very
accurately and precisely using non-invasive
technology. Furthermore this system was based
on software modules identical to the invasive
CAS technique meaning that most of the
measurements taken with non-invasive and
invasive systems were identical. Therefore, for
the first time, a non-invasive system could
assess knee kinematics in more realistic
conditions (i.e. standing full weight bearing or
under varus or valgus stress) which would help
to adjust more appropriately intra-operative
soft tissue management. As mentioned already
the varus/valgus envelope could be reliably
measured within the first 40° of flexion, which
was enough to detect mid-flexion instability.
These tools still in development are certainly
key to the success of future knee arthroplasty
surgery [49-54].
In at least two of our studies, we clearly
demonstrated that there is a difference between
the supine alignment and standing alignment
which means that maybe the ideal a leg
alignment after TKAshould be 2 or 3° of valgus
instead of 0° (180 degrees) to conform to a
balanced knee. However, whatever the goal,
CAS proved to be an invaluable device to set
whatever angle has to be done to optimize the
knee functional outcome. Uncertainty still
remains as far as functional outcomes are
concerned after CAS TKA.
The new generation of
CAS for a savvy
generation
[61]
The frame of reference used to guide knee
replacement in CAS has been extensively
validated and confirmed to be very reliable and
very reproducible to orient the jigs and implant
components. Most of the CAS systems used
today are infra-red (IR) technology and showed