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Introduction
In Greek mythology, Procrustes was a smith
and bandit, who tortured passing travelers by
forcing them to fit onto his iron bed, by
stretching those who were too short or
amputating those who were too tall. Today, a
“Procrustean bed” describes an arbitrary
standard to which rigid conformity is
enforced.
A long held tenet in total knee arthroplasty
(TKA) is that long term survival and optimal
function are dependent on achieving a post-
operative limb alignment within 3° of the
neutral mechanical axis. To this end, computer
navigation and now patient specific
instrumentation have been developed, to
improve accuracy in implantation andmaximize
the number of arthroplasties falling within
these limits. At the 9
e
Journées Lyonnaises de
Chirugie du Genou in 1999, Rivat and Neyret
presented that residual varus of femoral origin
was acceptable, but neutral mechanical
alignment of the tibial component was
mandatory1. More recently, a number of
authors have also challenged this principal,
suggesting “malalignment” may have little
effect on the outcome of knee arthroplasty
performed with modern prostheses and
techniques.
Anatomyand Deformity
To describe the anatomy and alignment of the
lower limb, a number of descriptive terms are
used. The anatomical axis of each bone refers
to a line drawn along the centre of the
intramedullary canal. The mechanical axis of
the femur refers to a line drawn from the centre
of the femoral head to the centre of the knee.
For the tibia, the mechanical axis refers to a
line between the centre of the knee and the
centre of the ankle. The anatomical and
mechanical axes of the femur form an angle
around 6°, while the two axes of the tibia are
usually equivalent.
The angle formed by the distal femoral joint
surface and the mechanical axis is referred to
as the mechanical lateral distal femoral angle
(mLDFA) and is typically 3°, whilst the
anatomic lateral distal femoral angle (aLDFA),
formed by the anatomic axis and the joint
surface, is usually 9°. The tibial joint surface is
usually 3° varus to the mechanical axis, and is
referred to as the mechanical medial proximal
tibial angle (mMPTA).
The global mechanical axis, referred to as
Maquet’s line, describes a line drawn from the
centre of the femoral head to the centre of the
talus [2]. Normally, this line passes through the
Coronal Alignment After
Total Knee Arthroplasty:
A Victim of Procrustes
Syndrome?
T. Lording, S. Lustig, P. Neyret