THE EFFECT OF POSTERIOR TIBIAL SLOPE ON THE KINEMATICS OF PCL-RETAINING TKA

Abstract

In PCL-retaining TKA, tension in the PCL is sensitive to changes in the posterior slope of the tibia component. However, it is not understood how PCL tension, in combination with the absence of the ACL, affects knee kinematics. This study demonstrates the effects of varying posterior tibial slope on the tibiofemoral and patello-femoral kinematics after PCL-retaining TKA.

Eight fresh-frozen lower limb specimens were mounted in a kinematic knee simulator. External forces were applied to create a deep knee bend from 0–110 degrees of flexion, while the three-dimensional motions of the femur, patella and tibia were tracked in real time using a motion analysis system. A PCL-retaining TKA was implanted into each cadaver with the tibial component matching the natural posterior slope of the tibia. After testing, the tibial slope was reduced by four degrees compared to the natural slope, then increased by four degrees compared to the natural slope. With each change in slope, the kinematics of the knee were recorded.

A dramatic change in femoral rollback was observed with increasing slope of the tibial component. In full extension, matching the natural tibial slope displaced the femur 5.7 ± 1.5 mm posteriorly, while more anterior slope and more posterior slope displaced the femur 5.1 ± 2.6 mm and 8.7 ± 2.0 mm posteriorly, respectively. Paradoxically, increased posterior slope resulted in less rollback of the femur during flexion. At 100° a of flexion, total rollback was 11.8 ± 2.6 mm in the intact knee, 6.9 ± 2.4 mm with the natural slope, 9.0 ± 2.8 mm with the anterior slope, and 5.7 ± 2.3 mm with the posterior slope.

Preserving the PCL allows the femur to rollback on the tibial plateau with knee flexion. However, increasing the natural slope of the tibia causes a significant posterior shift of the femur in extension thus reducing rollback in flexion.