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Today there is an increasing awareness amongst
knee surgeons about the individual variability
in anatomical shape of the knee and natural
alignment of the leg. Nevertheless we continue
to treat our patients on a relatively uniform
basis, using a limited set of standard component
sizes and shapes, and a surgical technique
aiming at zero degree mechanical limb
alignment in all of our cases.
This dogmatic approach has nevertheless been
relatively successful in the past, with acceptable
results in terms of pain reduction and restoration
of functionality. Despite this, many patients
with artificial knee replacement however
continue to experience functional limitations
and discomfort in the operated joint, especially
when compared to healthy, non-operated peers
of the same age.
The inability to restore the individual’s anatomic
configurationwith our current prosthetic designs
and surgical techniques may be an important
factor in this. The quest towards individualized
surgical strategies and implants in order to
restore the patients individual pre-diseased
profile or status is therefore an attractive path
onto which knee surgeons and implant designers
have recently embarked. The recent progress in
understanding the effect of certain factors such
as gender, morphotype, and native alignment
have lead to a better understanding of the
constituents that determine the individual profile
of the patient’s knee, and these are therefore the
basis towards a potentially more successful
artificial reconstruction of the knee joint.
In this chapter we will focus on each of these
factors, starting with the patient’s pre-diseased
alignment.
Constitutional
alignment
The main purpose of either partial or total knee
arthroplasty has always been to replace the
eroded cartilage and bone by an artificial
implant, usually out of metal and plastic and
which compensates for the erosion or damage.
Whendoing so, restorationof neutralmechanical
alignment has traditionally been considered as
the most important factor with respect to the
durability of the implant. When neutral
mechanicalalignmentisrestored,themechanical
axis of the leg passes through the centre of the
knee, which leads to an even mediolateral load
distribution and a minimized risk for implant
wear and component loosening. For this reason,
several techniques to obtain intraoperative
restoration of mechanical alignment have been
used in the past, usually by referencing from
intramedullary or extramedullary alignment
rods, or using more sophisticated computerized
navigation methods.
Anatomy, kinematics an knee
prostheses; 3D variations in
knee anatomy?
J. Bellemans, J. Oosterbosch, J. Truijen