During activities of daily living (ADL), varus moments are experienced in the knee, which can result in frontal plane rotation, or liftoff, of the lateral femoral condyle with respect to the tibial plateau. An understanding of this rotation is valuable as it could potentially lead to contact between the femoral component and polyethylene post of a total knee replacement (TKR). Therefore, the purpose of this study was 1) to assess how much frontal plane rotation was achieved due to varus moments imposed on a total stabilized (TS) TKR from the stair ascent activity, and 2) to determine whether a TS TKR could withstand the contact stresses imposed by the varus loading for 1 million cycles without the post fracturing or plastically deforming. A PS femoral component paired with a TS polyethylene insert and baseplate (Triathlon, Stryker, Mahwah, NJ) were aligned on a multi-axis testing system (MTS Systems Corp, Eden Prairie, MN) (Figure 1). Size 1 components were used as they represented the worst-case size for testing. The femoral component was fixed at 60 degrees of flexion, representing an angle of peak varus moment during stair ascent [1]. The peak varus moment used in this study was determined by scaling the data from In order to evaluate the frontal plane rotation achieved due to the varus moment with minimal influence from other loads, an FEA model of the physical test setup was used to determine the lowest joint compressive load that would allow testing to be stable. Given this, testing was completed with a constant joint compressive load of 1500 N (33% of that reported by Lastly, a validation test was run on a component with the polyethylene post notched at the medial distal aspect. The post fractured during testing indicating that the test could induce the clinical failure mode of interest.INTRODUCTION
METHODS
