Effects of Tibial Insert Slope on Polyethylene Wear and Stress

INTRODUCTION: Both posterior stabilized (PS) and cruciate retaining (CR) total knee replacement systems have demonstrated high rates of survivorship, high clinical knee scores and high patient satisfaction scores for decades. However, CR total knees sometimes exhibit more varied kinematics and a smaller range of motion than similar PS knees. Many factors can cause this, but one important factor may be a posterior cruciate ligament (PCL) that does not optimally perform with a given tibial slope. One option proposed for achieving a well-balanced PCL is a tibial insert available with a variety of posterior tibial slopes in addition to choices in size and thickness. However, tibial insert slope variation, defined by the angle formed between the distal and proximal faces of the insert, redistributes ultra-high molecular weight polyethylene (UHMWPE) insert thickness in the sagittal plane, which may have an effect on wear performance. The objective of this study was to evaluate the effects of tibial insert slope on UHMWPE wear by using finite element analysis (FEA) and an in-vitro wear test to compare a standard CR tibial insert with a corresponding sloped version. The hypothesis tested was that tibial insert slope variation has little effect on UHMWPE wear.