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This asymmetry between the two parts of the
tibial plateau can be managed only using
dedicated tibial components for the medial and
the lateral compartments (fig. 1). We use a
semicircular tibial component for the lateral
compartment and an anatomic component the
medial side. This is the unique way to closely
adapt the prosthesis to native anatomy.
Position of the
femoral component
The position of the femoral component should
be ideally perpendicular to the center of the
tibial component during both flexion and
extension in order to achieve more surface
contact and avoid peak wear. Till 10° of
obliquity in flexion are acceptable. To obtain it,
surgeons must keep in mind that at the last 20°
of knee extension, external rotation of the tibia
occurs and locks the knee (position of maximal
stability) [10, 11].
Consequently, a centered femoral implant in
flexion may lead to an excessive internal
rotation in extension and impingement on the
tibial spine eminence.Therefore, the positioning
in flexion should exaggerate the lateral rotation
and the lateral positioning. In the lateral
compartment, this should be obtained even
retaining lateral osteophytes.
Moreover, femoral component orientation
should follow the condylar axis (fig. 2).
Fig. 2: The femoral component should be placed as
lateral as possible and along the axis of the femoral
condyles.
Fig. 1: The medial and lateral parts of the tibial plateau have different
shapes which can be replaced adequately only with dedicated tibial
components.