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Coronal Alignment After Total Knee Arthroplasty: A Victim of Procrustes Syndrome?
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Bonner and coworkers found a weak trend
towards a higher revision rate in those outside
the 0°±3° range, however this fell short of
statistical significance (p=0.47). They con
cluded the relationship between mechanical
alignment and survival for primary TKA is
weaker than previously reported.
With regards to function, two medium term
studies have suggested functional outcome is
not adversely affected by residual post-operative
varus alignment. From a series of 218 primary
TKAs, Matziolis and colleagues compared the
results of the 30 knees with the greatest post-
operative varus alignment, to neutrally aligned,
matched controls [21]. The varus group had a
mean post-operative mechanical axis deviation
of 6.3° (3.9-10.7°). There was no difference in
functional results using multiple validated
measures, and no revisions in either group at a
minimum five year follow-up. Magnussen and
colleagues, from the Centre Albert Trillat in
Lyon, examined the results of 553 TKAs for
varus osteoarthritis, comparing those with with
neutral post-operative mechanical alignment
(0°±3°) and those with residual varus alignment
greater than 3° at mean follow-up of 4.7 years
[22]. They found no difference in
Knee Society
Score
(KSS) or revision rate between the two
groups, provided the residual varus was femoral
in origin. Tibial component varus and femoral
component valgus were both associated with
inferior KSS results.
One recent study has found superior functional
results for TKAs with mild residual varus. In a
study of 143 consecutive TKAs for varus OA,
Vanlommel et al observed that the 46 knees
with residual varus of 4-7° (FTMA 174-177°)
demonstrated significantly better KSS and
Western Ontario and McMaster University
Osteoarthritis Index
(WOMAC) scores than
the neutral and significant varus groups at an
average of 7.2 years [23].
Discussion
A number of criticisms have been made of
early studies showing decreased survivorship
with non-mechanical alignment. Most used
only short-leg radiographs for assessment [6, 8,
9] and involved early prosthesis designs no
longer in use today [10]. Polyethylene quality
was inferior, and sterilization methods were
employed now known to cause material
property degradation [18].
The literature regarding functional outcome is
unclear. Most data comes from studies into
navigation in TKA, examining short to medium
term results. Some authors have reported
improved knee function with more ideal
alignment [24-26]. Others have found no
improvement and even poorer functional
results using navigation [27-30]. A systematic
review in 2012 concluded there was improved
coronal plane alignment but no functional
improvement with navigation [31], however a
recent meta-analysis did find improved function
in the navigation group [32].
Recently, Bellemans and coworkers have
introduced the concept of constitutional varus,
suggesting a neutral mechanical axis may be
abnormal and even undesirable for many
patients [33]. In their study, 32% of men and
17% of women had a natural mechanical
alignment ≥3° of varus. Similarly, others have
explored they cylindrical axis of the knee [34]
and the concept of kinematic alignment [35].
Howell and coworkers reported equivalent or
slightly betterWOMAC and Oxford knee scores
(OKS) for for varus and valgus outlier groups in
198 kinematically aligned TKAs, although this
did not reach significance. Dossett
et al.
, in a
randomized control trial, evaluated the short
term outcomes of 41 kinematically and 41
mechanically aligned TKAs [36]. Whilst the
overall limb alignment was similar, the
kinematic alignment group had 2.3° more tibial
component varus and 2.4° more femoral
component valgus. KSS, WOMAC and OKS
were superior in the kinematically aligned
group. Whilst there were no catastrophic early
failures in either study, the long term outcome
of kinematically aligned TKA is unknown, and
the accuracy of the patient specific instrumen
tation systems required to achieve kinematic
alignment are still being investigated [37, 38].