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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: Characterisation of wear particles generated during accelerated testing of total hip replacements

Author: HUSSAIN, A

Year: 2005

Supervisor(s): Julia Shelton

This hip simulator study has shown that the size distribution of wear particles generated in tests on 5 MRads crosslinked polyethylene can be influenced by the degree of patient activity. Fast jogging showed a greater influence on the number of sub-micron-sized wear particles (5-fold increase compared to walking) than on volumetric wear rate (26 mm3/106 cycles compared to 20 mm3/106 cycles). Fast jogging also did not generate the largest wear particles (>10 μm) produced by normal walking. Roughening of the Co-Cr-Mo femoral heads created a 1700-fold increase in the numbers of sub-micron PE particles under fast jogging. The clinical significance of this result suggests that highly active PE patients will generate high numbers of bioactive PE wear particles within the accepted bioactive range, 0.2-10μm.

Metal-on-metal (MOM) hip arthroplasty has also seen rapid growth worldwide. However, there remains concern over their long-term biocompatibility due to systemic ion release. Therefore, the aim of this current investigation was to test the hypothesis that larger diameter MOM bearings (greater than 40 mm) will generate smaller Co-Cr-Mo wear particles compared to a 28 mm size bearing, and reduce the total wear particle surface area, and to test the hypothesis that ‘severe’ gait conditions will greatly increase the size of Co-Cr-Mo wear particles, thereby causing a sizable increase in wear particle surface area. Walking with a 28 mm bearing produced the largest amount of at 0.92 mm3/106 cycles, whereas the 40 mm and 56 mm bearings, generated lower wear rates at 0.39 mm3/106 cycles and 0.321 mm3/106 cycles respectively. Simulated fast jogging created a 3-fold increase in the number of elongated (needle) wear particles compared to normal walking.