Wear of Polyethylene Against Oxidized Zirconium Femoral Components: Effect of Aggressive Kinematic Conditions and Malalignment in Total Knee Arthroplasty

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Abstract

Metallic femoral components with ceramic articulating surfaces can substantially lower polyethylene (PE) wear during walking activities under conditions of normal knee alignment. It is unknown whether these types of components can maintain low wear rates under conditions of knee malalignment and the harsher kinematics associated with younger, athletically active patients. Wear was measured in non–cross-linked, ethylene oxide–sterilized PE inserts against oxidized zirconium or cobalt-chrome femoral components in a knee wear simulator. The vertical load was modified to replicate knee varus malalignment of 3°, and the range of tibial rotation was increased to 20°. Mean gravimetric and volumetric wear rate over 5 million cycles was 55% lower in the oxidized zirconium group. An oxidized zirconium femoral component can significantly reduce PE wear under simulated conditions of athletically active patients with modestly malaligned total knee arthroplasty prostheses.

Section snippets

Methods

Three oxidized zirconium Profix (Smith & Nephew, Memphis, Tenn) femoral components and 3 femoral components (Fig. 1) of identical geometry made of an alloy of cobalt-chrome-molybdenum (Co-Cr) were mounted in a 6-station displacement-controlled knee wear simulator (AMTI, Watertown, Mass). The femoral components were articulated against 6 tibial PE inserts (non–cross-linked, sterilized by ethylene oxide) in modular tibial base plates. The lubricant used was 90% bovine serum supplemented with EDTA

Results

Oxidized zirconium femoral components reduced PE wear by 55% compared with cobalt-chrome components under conditions of varus malalignment and excessive tibiofemoral rotations (Table 1). Mean gravimetric wear rate was very linear (R2 > 0.99) over 5 million cycles and consistently lower in the oxidized zirconium group (Fig. 3). Volumetric wear calculated from the surface mapping technique showed similar but slightly lower overall wear rates, as compared with the gravimetric measurements between

Discussion

In a previous study of the same material and component design at our laboratory, it was shown that tibial PE wear was substantially reduced when oxidized zirconium femoral components were used under so-called benign testing conditions (based on ISO standards) [21]. Compared with our previous study, we found that increased tibial rotation together with increased medial loading almost doubled the wear in the cobalt-chrome groups (20-39 mg per million cycles). The wear rate also increased in the

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    The Conflict of Interest statement associated with this article can be found at doi:10.1016/j.arth.2011.06.002.

    This study was funded with research support from Smith & Nephew.

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