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Restoration of neutral mechanical alignment is
since a long time considered as one of the key
factors for successful total knee replacement.
The fact that neutral mechanical alignment is
associated with improved implant durability
when compared to knees that have not been
restored to neutral, is well documented in
literature. Several published series from the
eighties and nineties have indeed shown
increased polyethylene wear, osteolysis, and
implant loosening in knees that were not
restored to neutral [1-7]. It is generally accepted
that these adverse events occur due to the fact
that deviations from neutral mechanical
alignment lead to increased mechanical loads
on the implant as well as the bone-prosthesis
interface, leading to subsequent implant and/or
fixation failure.
In recent years however, material properties,
polyethylene quality as well as implant fixation
have improved significantly, to such an extent
that modern TKAmight be less subject to these
issues that were of concern in the past. Recent
literature seems to confirm this [8-11]. Several
recent studies have indeed failed to demonstrate
an inferior outcome for so-called malaligned
versus neutrally aligned knees when modern
implants and a contemporary surgical technique
was used.
As a consequence of this, the concept of
restoring anatomic rather than mechanical
alignment has gained interest. In this philosophy
the natural alignment of the knee is restored to
its original state that was reached at skeletal
maturity, before the disease or damage had
occurred. The authors have defined this as the
patient’s constitutional alignment [15].
Such approach would not necessarily restore
the alignment to neutral; it was indeed recently
demonstrated that a significant number of
patients have a constitutional alignment that
deviates from neutral. For example, the
proportion of individuals with constitutional
varus (≥3°) was as high as 32% in males and
17% in females in the author’s study [15]. This
number may seem relatively high at first sight
and underrecognised in the past. The reason for
this is that many of the classic alignment studies
have been flawed with several shortcomings,
such as a limited number of participants, a large
variability in the subject’s age, recruitment in a
hospital setting, lack of stratification and
selection bias of the subjects.
Patient’s with constitutional varus have since
their end of growth always had varus alignment.
It is logical to assume that restoring neutral
alignment in these patients would feel abnormal
What is the optimal
alignment in TKA ?
J. Bellemans, J. Oosterbosch, J. Truijen