Wear Testing of UHMWPE Tibial Components: Influence of Oxidation

[+] Author and Article Information
Sarah K. Young, Tony S. Keller

University of Vermont, Department of Mechanical Engineering, 201 Votey Bldg., Burlington, VT 05405

Keith W. Greer

Depuy Orthopaedics, Inc., Polymer Research and Development, 700 Orthopaedic Drive, Warsaw, IN 05405

Michael C. Gorhan

Codman, Neuro Intensive Care Unit, 325 Paramount Dr., Raynham, MA 02767

J. Tribol 122(1), 323-331 (Jun 30, 1999) (9 pages) doi:10.1115/1.555362 History: Received February 02, 1999; Revised June 30, 1999
Copyright © 2000 by ASME
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AMTI Dynamic Knee Machine station. The top portion of the picture shows a femoral component (a) cemented to a custom made fixture (b). Below the femoral component, an UHMWPE tibial insert (c) and a tibial tray (d) are cemented into the tibial fixture (e). Rollers (f ), mounted on top of an AMTI six degree-of-freedom load cell (g), hold the tibial fixture in place and allow it to slide freely in the medial/lateral direction. The medial and lateral condyles are labeled with M and L, respectively.
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Vertical DKM loading curves obtained over one cycles (0.5 seconds) per test interval (0–300,000, 300,000–1 million, 1 million–2 million, etc.) shown for each type of loading (walking, ascending, and decending stairs) and both phases of testing (black lines—test phase 1, gray lines—test phase 2).
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DKM gravimetric wear of the high and low oxidation sample groups over the test interval from 0.3 to 5 million cycles. Group mean values are indicated by ▪ and the error bars represent the standard error of the mean at each measurement interval. Differences between the wear rates of the two groups approached, but were not statistically significant (p>0.1).
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Photomicrographs of tibial condyles after various numbers of cycles. (a) Medial condyle of low oxidation sample L3 after 5 million cycles, illustrating burnishing. At 300,000 cycles the burnished areas were slightly smaller and lighter, but looked very much the same. (b) Medial condyle of high oxidation sample H2 after 2 million cycles, illustrating subsurface cracking. The cracked region is outlined. (c) Medial condyle of sample H2 after 3 million cycles, illustrating delamination wear. (d) Higher magnification (approximately 1.5×) of medial condyle of sample H1 after 5 million cycles showing cracking and delamination.
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Photomicrographs of a selected region of the lateral condyle of sample H1 with back lighting to accentuate subsurface cracking. (a) Wear after 2 million cycles (shown magnified approximately 3.4×). The damage is very localized and cracks are beginning to reach the surface at the posterior edge of this region, indicated with arrows. (b) Wear after 3 million cycles (shown magnified approximately 2.6×). The dark line, indicated with arrows, is a crack which clearly breaks through to the surface. Subsurface cracking propagated out from the most severely damaged area, in the region to the right of the dashed line.




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