Abstract
Wear of the polyethylene (PE) insert in total knee replacements can lead to wear-particle and fluid-pressure induced osteolysis. One major factor affecting the wear behaviour of the PE insert in-vivo is the surface characteristics of the articulating femoral components. Contemporary femoral components available in Canada are either made of cast Cobalt Chromium (CoCr) alloy or have an oxidized zirconium surface (Oxinium). The latter type of femoral components have shown to have increased abrasive wear resistance and increased surface wettability, thus leading to reduced PE wear in-vitro compared with conventional cast CoCr components. Although surface damage has been reported on femoral components in general, there have been no reports in the literature as to what extent the recommended operating techniques affect the surface tribology of either type of femoral component.
Twenty-two retrieved total knee replacements were identified with profound surface damage on the posterior aspect of the femoral condyles. The femoral components were of three different knee systems: five retrievals from the NexGen(r) total knee system (Zimmer Inc., Warsaw, IN), twelve retrievals from the Genesis II(r) total knee system (CoCr alloy or Oxinium; Smith & Nephew Inc., Memphis, TN), and five retrievals from the Duracon(r) total knee system (Stryker Inc., Mahwah, NJ). Reasons for revision were all non-wear-related and included aseptic loosening in two cases, painful flexion instability, and chronic infection. All retrieved femoral components showed evidence of surface damage on the condyles, at an average of 99° flexion (range, 43° – 135° flexion). Titanium (Ti) alloy transfer and abrasive surface damage were evident on all retrieved CoCr alloy femoral components that came in contact with Ti alloy tibial trays. Surface damage on the retrieved Oxinium femoral components was gouging, associated with the removal and cracking of the oxide and exposure of the zirconium alloy substrate material. CoCr alloy femoral components that had unintended contact with CoCr alloy tibial trays also showed evidence of gouging and abrasive wear.
All femoral components showed severe surface damage in the posterior aspect of the condyles. The femoral surface was heavily scratched and the oxidized zirconium coating surface appeared removed. The surface analysis suggested that the surface damage most likely occurred during the time of initial implantation. In particular, it appeared that the femoral condyles were resting on the posterior aspect of the tibial tray in flexion, thus scratching the femoral components. Such scratches could potentially lead to accelerated PE insert wear and reduced implant longevity, thus making expensive revisions surgery necessary. The authors strongly suggest a revision of the current operating techniques recommended by the implant manufacturer to prevent this type of surface damage from occurring.
