Introduction

A tibial insert with choices in size, thickness, and posterior slope is proposed to improve ligament balancing in total knee arthroplasty. However, increasing posterior slope, or the angle between the distal and proximal insert surfaces, will redistribute ultra-high molecular weight polyethylene (UHMWPE) thickness in the sagittal plane, potentially affecting wear. This study used in-vitro testing to compare wear for a standard cruciate-retaining tibial insert (STD) and a corresponding 6° sloped insert (SLP), both manufactured from direct-compression molded (DCM) UHMWPE. Our hypothesis was slope variation would have no significant effect on wear.

Introduction

While clinically successful for decades, CR TKA is persistently compromised by inconsistent PCL function. Problems of mid-flexion instability, incomplete knee flexion, erratic kinematic behavior and posterior instability, not seen with PS devices, raise concerns about the consistency of the technique, and the devices used. Most TKA systems offer at least 2 different geometries of tibial inserts to address this clinical problem.

We hypothesize these problems are a result of compromise of PCL anatomy. To avoid compromise to the PCL 3 steps are required: 1) The slope of tibial resection must be less than 5°; 2) the depth of tibial resection must be based off the insertion footprint of the PCL, not the deficiencies of the tibial articular surface; and 3) the tibial insert must be modified to allow intraoperative balancing of the PCL.