7 Alignment and Set-Up
Users be aware of potential finger trap hazard
Note:
4-bar knees inherently are very stable due to the geometry built into each design. This
is commonly referred to as the Instant Knee Center (IKC). The IKC point when doing bench
alignment, will fall behind the traditional TKA line that we will reference. (Fig. 2,3) Tg line in
Fig. 3 is ideal placement, but in certain instances, it may be necessary to accommodate
placement anteriorly (into the T1 zone
up to 2mm
), or posteriorly (into the T2
zone up to
2mm)
. The Tg line is referencing a moving weight bearing line, so it could be in T1, neutral,
or in T2 zones.
BENCH ALIGNMENT:
a) With prosthesis assembled, taking into account hip flexion contractures, abduction, Line Of
Progression, and toe out (Fig.2), the TKA plumb line should pass through the knee center (at
the proximal/anterior pivot – red dot pivot Fig.3) and in front of the K point (IKC).
Take into account shoe heel height, and add 3mm safety factor
.
Set the bench alignment taking into account the heel height of associated footwear plus 3mm
safety factor!
It is not recommended to have alignment posterior to the reference line, as it
could cause knee instability!