WEAR OF RETRIEVED HIGH-DOSE CROSS-LINKED POLYETHYLENE SOCKETS IN LONG-TERM CLINICAL USE

Abstract

Introduction: In 1970’s, Oonishi et al found out that the polyethylene cross-linked by gamma-ray irradiation (dose=100Mrad) had high wear performance, and then clinically used it as the material for acetabular sockets. He has reported excellent outcomes. In this study, we measured the wear three-dimensionally, and the oxidation by microscopic Fourier transform infrared spectrophotometry in retrieved high-dose cross-linked polyethylene [100Mrad PE] sockets implanted over 25 years.

Materials and methods: We revised two 100Mrad PE sockets (SOM type manufactured by Mizuho medical (JAPAN)), due to aseptic loosening, which had been implanted for 27 years approximately. The liner and volumetric wear were measured as previously reported [1]. Measuring points for oxidation index were (1) near surface point in unworn area, (2) near surface point in worn area, and (3) inner area which left any surface by > =2.5mm.

Results and discussion: The liner wears were 0.06mm and 0.29mm respectively. The volumetric wears were 25.8mm3 and 91.8mm3. The liner-wear rate of them were 0.002mm/year and 0.010 mm/year. The oxide index of each socket was 0.75, 0.62, 0.25 and 1.73, 0.67, 0.28, in order of the unworn area, the worn area and the inner area. Many researchers have reported that the annual liner-wear rate of UHMWPE sockets is from 0.1 to 0.2mm/year. We showed extremely less wear rate of the 100 Mrad PE sockets in comparison with UHMWPE sockets. Oxidation index in the worn area was approximately the same as that of UHMWPE sockets, which were determined in our previous study [2]. These results showed that 100Mrad PE sockets had maintained the high performance to the wear for long-term clinical use.