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well as better soft tissue balancing [21] could
explain slightly better adduction moment espe-
cially with biphasique moment pattern being
more frequent in navigated knees. Hilding
found unstable TKAs have lower peak adduc-
tion moment (27.6 Nm compared to 30.9 Nm)
so these results are at least going in the right
direction. However Schache
et al.
[9] had peak
adduction moments at the knee of between 0.5
Nm/kg and 1.0 Nm/kg so these results are the
lower end. Andriacchi also showed higher
adduction moment related to increase OA
severity [12]. Therefore, it is hard to see from
the literature what we would expect.
Biphasique moment pattern is a consistent
finding in normal subject. Abnormal
biphasique pattern in flexion or extension is
also a usual characteristic after TKA [12]. We
found biphasique pattern in 80% of navigated
knees versus 45% in conventional. Biphasique
pattern after TKA has been identified by
McClelland as a reliable feature to identify
successful functional outcome [10]. After a
year, both groups had similar Oxford scores
and ROM, and actually biphasique pattern fre-
quency might identify better long term func-
tional outcomes but only the future will show.
However, it seems quite obvious that even
with better gait cycles navigated knee are dif-
ferent from control group which suggests that
the knee design makes the difference [8].
Finally with regard to ROM which has been
found significantly better in navigated knees
but still not comparable to control group, nor-
mal range ROM in physiological walking
range from a few degrees flexion (~5°) to 60
degrees of flexion. Detection of ROM impair-
ment is obviously seen in other circumstances
such as stairs negotiations. Our study has iden-
tified differences between the two groups in
descent and ascent of stairs. Stair ascent usual-
ly requires greater knee flexion up to
20 degrees with respect to walking flexion
angle as well as short percentage of gait cycle.
Descent stairs requires similar ROM than
ascending stairs but a longer gait cycle time.
Both conventional and navigated groups were
different from the control group which con-
firmed kinematics changes in TKA. However
navigated knee did better. Again better gap and
soft tissue managements with navigation could
explain this result.
CONCLUSIONS
Computer navigated TKA results in an
improved dynamic functional outcome com-
pared to using a standard instrumentation
method. However, navigation could not allow
the knee to recover a normal kinematics as we
found in the control group. Only long term fol-
low-up might confirm that better gait pattern
will result in better long term satisfactory
functional outcomes.
Acknowledgements
D
r
Angela Deakin for the manuscript review.
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