Low wear and friction in alumina/alumina total hip joints: a hip simulator study

We studied the wear of state-of-the-art alumina/alumina total hip joints with the uniaxial five-station, and the three-axis single-station hip joint simulators of Helsinki University of Technology. The diameters of the joints were 26, 28 and 32 mm. Visual examination and weighing of the components showed no wear. Scanning electron microscopy showed that (a) the wear marks were slight, consisting of removal of grains, multidirectional grooving and mild abrasion, (b) the wear mechanisms were similar to those seen in components removed from patients, and (c) there was no marked difference in the specimens worn in the uniaxial vs. three-axis simulator. The coefficient of friction was measured throughout the 5 million cycle wear test with the three-axis simulator. The average value was 0.007. We conclude that alumina/alumina joints had low wear and friction under the present test conditions. The results are promising, since minimal wear is one of the prerequisites for long-term success in prosthetic joints.