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The goals of total knee arthroplasty (TKA) are
to implant a balanced, stable knee prosthesis,
which alleviates arthritic pain and gains range
of motion and function. Obtaining an optimal
result in TKA is a complex task and consists of
a series of surgical decisions, which usually
follows a set algorithm. With recent advances
in material technology, poor outcomes from
TKA usually do not relate to wear of the
polyethylene spacer, but rather due to inaccurate
implantation of the prosthesis and inattention
to the soft-tissue envelope. This can present
with pain, instability or poor range of motion or
a combination of all of these symptoms.
Obtaining a TKA that is well balanced is a key
factor in obtaining an optimal result.
There are many philosophies and techniques
that can be used to obtain a balanced TKA.
Ultimately the technique used must be accurate,
reliable, reproducible, and reduce the potential
for systematic error as much as possible.
Implantation of a TKA is an equation with
numerous unknown factors, however all of
these unknown factors are linked. And as all
TKA techniques rely on a series of dependent
and linked steps, small errors, especially if they
occur early in the procedure often lead to a
magnified problem in the final outcome.
In order to obtain a balanced TKA there is a
series of bone cuts and soft-tissue releases that
should lead to similar spaces or gaps between
the tibia and femur in flexion and extension.
Bone cuts are determined by their orientation
and level. The orientation of the bone resection
occurs in two planes and three directions. The
level of the bone cut refers to its height or its
depth.
The tibial bone resection influences the size of
the flexion and extension gap evenly, however
it does not allow for correction of flexion and
extension gap balancing. The distal femoral
bone cut and the posterior femoral bone cut are
intimately linked to obtain even gaps. The
former leads to the extension gap and the latter
leads to the flexion gap and rotation of the
implant. They should both be the same in order
to obtain a balanced TKA.
The standard classical techniques for balancing
in TKA include a measured bony resection with
ligament balancing and a gap balancing
technique using the soft-tissue tension to
determine femoral bone cuts. The former relies
heavily on the orientation of the bone cut in
association with soft-tissue releases, whereas
the latter relies on the level of the bone cut
being equal in flexion and extension to provide
PSI and Ligament Balancing
in TKA
J. Robin, T. Zakaria, P. Neyret