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.

According to the knee simulator test results in 1970s, the total decrease in thickness of UHMWPE tibial tray in combination with ceramic femoral component [F-Comp] was less than one tenth as that of the combination with metal [1]. These advantages led to development of total knee prosthesis [TKP] with alumina ceramics. In this study, we report the wear surface observation, the clinical wear and the oxidation of the retrieved TKP used clinically for 23 years, comparing with a metal TKP.

The retrieved TKP was implanted in 1979, and retrieved on January 9th in 2002. This TKP consisted of an alumina ceramic F-Comp and a UHMWPE tray combined with a alumina ceramic tibial component. Observations of the surface of alumina F-Comp and UHMWPE tray were carried out using SEM. Shape of UHMWPE tray was determined three-dimensionally. Comparing the result with original shape based on the product’s plan, liner wear and volumetric wear were calculated. Oxidation index was determined by Fourier transform infrared spectrophotometry.

Alumina F-Comp did not have any scratch on the surface by seeing with naked eye. UHMWPE tray had deformation and scratches obviously. The liner wear rate was 37 micrometer/year and volumetric wear rate was 18.8 mm3/year. The oxidation indexes were 0.6 in the unworn area, 1.2 in the worn area and 0.2 in the inner area.

SEM observations of the F-Comp demonstrated no scratch or pit. In contrast, many scratches were clearly observed on the UHMWPE tray. However, higher magnification observations did not demonstrate severe wear, which was shown on the wear analysis of a metallic F-Comp. Oxidation degradation is a problem to solve. However, the low wear rate and mild wear pattern demonstrate that ceramic F-Comp reduced UHMWPE wear.