Polyethylene cross-linking by two different methods reduces acetabular liner wear in a hip joint wear simulator

Advances in cross-linking have led to the development of wear resistant ultrahigh molecular weight polyethylene for total joint replacement. This study compared wear reduction by two different cross-linking methods as measured in a hip wear simulator One highly cross-linked polyethylene was treated with 7.5 Mrad gamma irradiation with post-irradiation annealing and a sterilization dose of 2.5 Mrad (10 Gamma), while the other used 9.5 Mrad warm irradiation with 10 MeV, electron-beam (9.5 EB); Liners of the same design, made from nominally cross-linked (gamma sterilized) polyethylene were also tested. Gravimetric wear analysis was performed every 500,000 cycles for 5,000,000 cycle. After correcting for weight gain due to water absorption, the nominally cross linked liners demonstrated mean wear rates of 15.7 (+/-1.7) and 12.5 (+/-1.0) mg/million cycles. Both highly cross-linked polyethylene liners demonstrated significantly less wear than their respective controls (with mean rates of 1.5 (+/-1.2) and -1.4 ( +/-1.5) mg/ million cycle). The 9.5 EB liners gained Weight presumably due to increased fluid absorption, in addition, to that measured in loaded-soaked control implants. Any wear occuring was therefore assumed to have been more than offset by weight gain. Highly cross-linked polyethylene was significantly more wear resistant than non- or nominally cross-linked polyethylene. The differences in wear rates between the two highly cross-linked polyethylene designs (9.5 EB or 10 Gamma) are probably too small to be clinically significant. (C) 2003 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.