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The Development of a Third Body Wear Model
Bragdon, C., Daniel O'Connor, Muratoglu, O. K., Jasty, M., Harris, W. H.
Introduction
The purpose of this study was to design a third body wear model using a hip simulator and assess acetabular liners made of a new form of electron beam crosslinked UHMWPE (WIAM-95) with conventional polyethylene components.
Methods
The selection of the third body material, size and concentration were determined in a prior series of experiments. This study evaluated two types of particles, an aggressive test using 1µ sized alumina oxide particles at a concentration of 0.15mg/cc, and a test using 30µ sized PMMA particles, at the same concentration. The test method insured that the third body particles were kept in uniform suspension throughout the test. A baseline wear rate for each type of polyethylene was established without any added particles. Particles were added thereafter for an additional 5 million cycles for each particle type.
Results
Conventional liners had a baseline wear rate of 10.09±0.76 mg/million cycles. In contrast, the WIAM-95 liners had no measurable wear during the first million cycles, consistent with previous reports. There was an increase in the average rate of weight loss in both groups when alumina particles were added. In the conventional group, there was a steadily increasing rate of wear as the femoral heads were progressively damaged, giving a total average wear rate of 72.14±41.06 mg./million cycles. In contrast, the Durasul components had a significantly lower average wear rate 10.55±8.49 mg./million cycles, p< 0.01. The effect of the 30µ PMMA particles was less severe but the advantage of the crosslinking remained. The conventional components had an average wear rate of 19.37±4.84 mg/million cycles while the WIAM-95 components had no detectable amount of wear.
Conclusion
The issue of third body wear in vivo is very important for assessing new polyethylenes. This study describes a new wear model for assessing wear under third body debris conditions.
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