Page 8 - KNEETA

KNEETA R

Total Knee system

Many patients complain

of a loss of stability

due to total knee replacement, and this is sometimes called
anterior femoral sliding. In the literature this is referred to as
“paradoxical motion.” This term was made prominent by

This femoral sliding or “paradoxical motion” may be caused by an

that was designed to allow rollback. 1,2

In general, total knees may reduce the natural stability of the
knee. Instead of rolling back, the femoral component slides
anteriorly. This is considered a paradox because total knees
are designed to rollback, but instead they slide forward. In a

at approximately 20°, the weight of the body pushes the
femur forward along the tibia. The femur will continue to slide
forward until it’s stopped by the PCL or remaining musculature.
Furthermore, this sliding forward puts added stress on the
remaining soft tissues.

This “paradoxical motion” is also present in posterior-stabilized
knees. Many surgeons believe that posterior-stabilized knees are
1,2
unable to slide forward due to the post and cam articulation. This
has been shown in the literature to be false. Posterior-stabilized
total knee replacements slide forward until they contact the post.
In terms of the four-bar link theory, once the cam engages the
post, the rotational axis of a traditional posterior-stabilized knee
FIGURE 1 | Medial Pivot compartment becomes the post.

The MRI images shown in FIGURES 1 and 2 are visual examples of
how the normal knee moves. These were MRIs provided as part
3
of a study from Mr. Michael Freeman, a British surgeon, and Vera
Pinskerova, a Czechoslovakian PhD. The medial pivot compartment of
the tibial plateau is concave and “rocks” from a relatively posterior
contact to anterior contact. FIGURE 1 The meniscus, the center

moves forward with extension, but the medial pivot femoral condyle
does not.
3-5
Unlike the medial pivot side, the lateral meniscus moves forward with
the femur during extension. Thus, the tibiofemoral contact area
also moves forward with extension resulting in an arcuate zone of
contact. FIGURE 2

FIGURE 2 | Lateral compartment

SUNTEK
Medical Devices
and Electronic
Products Trade Co. KNEETA® Medial-Pivot Knee System
8 8