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The Wear Of Crosslinked UHMWPE In The Presence Of Abrasive Particles: Hip And Knee Simulator Studies
Laurent, M. P., Yao, J. Q., Gilbertson, L. N., Johnson, T. S., Swarts, D. F., Blanchard, C. R., Crowninshield, R. D.
Abstract
The reduction in in-vitro wear achieved with highly crosslinkedUHMWPE (HXPE) compared to conventional UHMWPE’s has beenwell documented in recent years. However, these data weremostly obtained under clean lubricant conditions. There ismuch less data pertaining to the wear behavior of HXPE underadverse conditions that may also have clinical relevance.This paper presents the results of hip wear tests performedwith bone cement (BC) and alumina particles added to the lubricantand of knee wear tests performed with the addition of bonecement particles.
Multifactorial hip wear tests were conducted to determinewear as a function of UHMWPE type (110 kGy e-beam irradiatedHXPE, conventional 37 kGy gamma irradiated UHMWPE), cup ID(22, 32 mm), aging condition (aged, nonaged), and abrasiveparticle type (bone cement, alumina). The hip wear tests wereperformed in a 12-station, biaxial rocking motion Shore Westernhip simulator, with the cup below the head, which was advantageousfor the ingress of particles into the articulating interface.As expected, the absolute wear rates are much higher in thepresence of alumina than bone cement particles (Figure 1).Conclusions from the hip studies include: (1) The wear advantageof the HXPE observed under clean conditions is largely preservedin the presence of the abrasive particles; (2) Under abrasiveconditions, the wear rates for the 22 mm liners were comparableto or exceeded that of the 32 mm liners, whereas under cleanconditions the wear rates are approximately linearly relatedto liner ID.
A knee wear test was also conducted, comparing the wear of72 kGy e-beam irradiated HXPE inserts and conventional 37kGy gamma irradiated controls in the presence of bone cementparticles. As seen in hip tests, the wear advantage of theHXPE is preserved (90% wear reduction in the presence of bonecement particles, versus 81% with clean serum) (Figure 2).A 40% increase in the wear rate was noted for the gamma controlswith the addition of the bone cement particles.
The preservation of the HXPE wear advantage, the unusual22 mm / 32 mm cup wear ratios, and the relative effects ofthe abrasive particles on the UHMWPE wear rates will be discussed.
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