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Contrary to these results, a number of authors
have reported inferior results associated with
tibial component varus [6, 16, 22, 39, 40].
Berend and colleagues, in a study of a cohort of
3152 knees, found tibial component varus of
more than 3° to significantly increase the odds
of failure (Hazard ratio 17.2, p<0.0001) [16].
In a later study from the same centre on an
expanded cohort of 6070 TKAs, Ritter
et al.
found increased revision rates when the tibial
component was implanted in varus, when the
femoral component was implanted with more
than 8° of anatomic valgus, and when one
component was implanted to “correct” for
malalignment of the other component, resulting
in neutral global limb alignment [39]. There
was no difference between those with neutral
tibial component and neutral overall alignment
and those with neutral tibial alignment and
overall varus limb alignment, suggesting some
residual varus global alignment in itself does
not compromise results.
Residual valgus alignment after TKA is
associated with inferior results. Karachalios et
al found residual deformity to be much more
common in valgus knees and associated with
significantly inferior clinical results using the
Bristol Knee Score [41]. Fang
et al.
reported a
revision rate of 1.5% for those with post-
operative valgus alignment compared to 0.5%
for those in neutral alignment, noting that those
with residual valgus tended to fail from ligament
instability [42]. Koskinen, in a study of 48
valgus knees implanted with cruciate retaining
prostheses, found residual valgus deformity to
significantly increase the risk of revision with
an odds ratio of 2 (95% confidence interval 1-3,
p=0.025) [43]. Eight of the fourteen revisions
were for progressive medial collateral ligament
(MCL) instability. Consistent with these clinical
reports, Bryant and coworkers, in a recent
cadaveric study, found valgus loading of a TKA
to significantly increase lateral tibio-femoral
contact pressures and MCL strain [44].
We feel avoidance of tibial component varus
and femoral component valgus is crucial for
the successful outcome of TKA. As described
by Rivat and Neyret in 1999, the origin of
deformity is an important consideration in TKA
[1]. When the deformity is articular, caused by
wear and osteophytes, this may be corrected
without asymmetrical bony resection leading
to ligamentous imbalance. When extraarticular
deformity is corrected, however, asymmetrical
cuts will result.
The single tibial cut contributes equally to both
the flexion and extension gap. In the case of
varus of tibial origin, an asymmetrical cut is
required to place the tibial component in neutral
mechanical alignment. This leads to medial
tightness, which may be balanced with a medial
ligament release.
On the femoral side, two bony cuts contribute
to the flexion and extension gaps. To correct
varus of femoral origin, an asymmetrical valgus
distal cut will require internally rotated
posterior condylar cuts to balance these gaps
(fig. 1). Internal rotation of the femoral
component is associated with patellofemoral
complications, pain, and increased failure rates
[40, 45, 46]. Considering the origin of femoral
varus deformity is often the proximal femur,
we feel it is best to accept a degree of femoral
component varus rather than risk imbalance
and component internal rotation.
Furthermore, tibial component varus and
femoral component valgus in a globally well
aligned knee will result in joint line obliquity.
Increased joint line obliquity is known to cause
increased shear forces after osteotomy [47],
and experimental data have supported this in
TKA [15]. Interestingly, a recent report found
coronal joint line orientation was not affected
in subjects with constitutional varus [48]. The
clinical implications of this finding have yet to
be studied.