Abstract
Total Knee Arthroplasty has proven to be a successful procedure for improving pain and function. Long-term studies have shown survivorship to be 90% or greater at 20 years. Most patients in those studies were over 60 years old. There has been a large increase in patients under 60 years old who are undergoing knee arthroplasty. Younger patients have much greater demands on the artificial articular surfaces. The average 55 year old is likely to perform two to three time as many gait cycles as the average 65 or 70 year old. Long-term studies demonstrate that polyethylene wear is a major cause of long-term failure.
Newer bearing materials such as cross-linked polyethylenes show promise in reducing wear in THA and more recently in TKA. Femoral component material can significantly influence wear. Studies reveal that in vivo femoral component scratching significantly increases polyethylene wear.
Oxidised Zirconium (OxZr) has been shown to significantly reduce polyethylene wear in knee simulators. The ceramic surface has greater lubricity and is harder. We have examined the in vivo performance on Oxidised Zirconium in several studies. These studies reveal that the harder Oxidised Zirconium femoral surface is much more resistant to scratching than CrCo femurs. Retrieval analysis revealed a 12 fold increase in scratching of CrCo femoral components compared to OxZr. Profilometry analysis of matched pairs of femoral components demonstrates that the surfaces of the CrCo implants significantly roughen over time while the OxZr do not significantly change in vivo. These comparative studies also showed less damage to the tibial polyethylene bearings with the OxZr femoral components compared to CrCo.
Extending longevity of TKA requires improved materials to reduced wear. To optimise this, bearing surfaces must be coupled with improvements in both tibial polyethylene and femoral component materials.
