Total disc replacement (TDR) devices have been restricted to designs with large, congruent articulations due to the limited wear properties of available materials. TDRs with more natural motion could be designed if materials were available which could resist the higher wear conditions. A novel TriLobe TDR design is self-centering and energetically stable, emulating the natural motion of the intact motion segment, but is not feasible using traditional materials due to small incongruent articulating surfaces. The objective of this study was to compare the wear properties of a medical grade polycrystalline diamond with wear properties of cobalt chrome (CoCr) and ultrahigh molecular weight polyethylene (UHMWPE) in aggressive high wear conditions. A modified pin-on-disc, crossing-path wear test was used to measure the wear rates of PCD-on-PCD, CoCr-on-CoCr, and CoCr-on-UHMWPE. The discs were placed in the inferior position on an oscillating plate, moving in a 10mm by 5mm figure-eight pattern. Pins had an initial 11.5mm radius and were loaded at 133N normal to the disc. In a typical pin-on-disc test, a wear flat develops on the pin and the wear rate is reduced as the contact area increases. The TriLobe design uses three lobes sliding in three non-conforming lenses which prevents wear flats from developing. To approximate this condition, the fixture holding the disc was placed on an air bearing and was allowed to rock in concert with movement of the load. The test was conducted in 25% bovine serum at a speed of less than two Hertz. Two sets of each material were tested, one set to 2.0 million cycles and the other set to 14.0 million cycles. Wear rates on the rocking-discs were measured using a high resolution coordinate measuring machine because the wear in the PCD specimens was not detectable gravimetrically.Purpose
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