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Many fluoroscopic kinematic studies describe
in CR retaining TKA paradoxical roll forward
of the femur in flexion indicating an incorrect
pcl tension. The variation of contact point in
CR TKA is larger than in PS TKA indicating
that correct balancing is difficult [1].
It is clear that PCL balancing in cruciate retai-
ning TKA is difficult to achieve. The PCL is a
strong central ligament with an oblique orien-
tation in the knee. It has its largest function
around 90 degrees of flexion and is the main
restraint against posterior tibial subluxation [2].
An important observation explaining the diffi-
culty of flexion gap balancing in CR TKA was
reported by Christen
et al.
[3]. They found a
strong relation between distraction of the
flexion gap and anterior translation of the tibia.
This anterior translation is caused by the
oblique orientation of the PCL in the knee
joint. A 2 mm increase of spacer thickness
could cause an anterior translation of the tibia
relative to the femur up to 4 mm. This indi-
cates that relatively small variations in gap
size can change the tibia position considerably
with respect to the femur. This relative posi-
tion of the tibia versus femur indirectly deter-
mines the contact point of the TKA after
implantation of the components.
The PCL tension can be too loose causing
increased laxity in flexion and causing para-
doxical femoral roll forward. This type of laxi-
ty in the flexion gap and the concomitant abbe-
rant kinematics can cause clinical symptoms
of PCL insufficiency with pain and instability
which is defined as a separate entity called
flexion instability [4, 5]. These knee joints
move anterior compared to the normal contact
point of the native knee at approximately the
posterior 2/3 of the AP-distance of the tibia
plateau [6, 7]. This change of contact point
causes reduction of the moment arm of the
extensor mechanism and increases patella
pressure.
The PCL tension can also be be too tight with
high tension on the PCL in flexion causing
limited flexion and pain. Also high PE pres-
sures and posterior insert wear are found in
these knee joints.
Theoretically one would expect a correct PCL
tension with a precise measured resection
technique in which the resected bone of femur
and tibia is replaced with prosthesis material,
thereby restoring the joint surfaces. This
would not change distances between ligament
insertions and the ligament tensions will
remain the same before and after replacement.
191
KINEMATICS OFANANATOMICLY-DESIGNED
CRUCIATE RETAINING TOTAL KNEE ARTHRO-
PLASTY IMPLANTEDWITHASPACER GUIDED
PCL BALANCING
A.-B. WYMENGA, P.-J.-C. HEESTERBEEK, L. LABEY, B. INNOCIENTI, P. WONG