Polycentric Versus Single Axis Sagittal Femoral Geometry and Paradoxical Anterior Translation in Total Knee Implants

Paradoxical anterior translation of the femur (undesirable anterior motion of the femoral side of the knee relative to the tibia) has been observed in patients with posterior cruciate ligament (PCL) retaining total knee devices in which the ACL is absent. Simulations of a double leg squat of several total knee implant designs were compared using measurements of tibio-femoral ‘contact positions’ similar to those published in fluoroscopic studies. The objective of the study was to examine if a femoral design with a single axis (single radius) of curvature in the para-sagittal plane undergoes paradoxical anterior translation in the same way as femoral designs with polycentric (multi-radius) geometry.