抄録
The objective of this study was to compare the wear mode of polyethylene (PE) cups run in a hip simulator to retrieved PE cups, and to evaluate the efficacy of the PE wear model.
Fifteen PE cups were tested in vitro: 3 at each of the irradiation doses 0, 2, 5, 50, 100 and 150 Mrad (in a 9 channel hip simulator, 6.2 million cycle duration, physiological load profile by Paul, 2000N maximum load at 1Hz using 30% bovine serum) .
Five retrieved PE cups were examined: there were three SOM cups (Mizuho Medical Instrument Co., COP alloy 28 mm head), of which one, given 0 Mrad, was retrieved after 8 years of clinical use, and two of which, given 100 Mrad, were retrieved after 15 years of clinical use. The other two were T28 PE 2.5 Mrad cups (Zimmer) : one after 18 years, and one after 13 years of clinical use. The cups were examined using a SEM (Philip XL30 FEG) for wear-scar locations and PE wear-topography.
Original machine marks were observed in the weight-bearing areas of the extensively cross-linked (ECL) in-vitro PE. No machine marks were observed for the 0 and 2.5 Mrad in-vitro cups and retrieved cups. The formation of more nodules and fibrils in the 0 Mrad cups, compared to the ECL cups (in-vitro and retrieved), was striking. The frequency of occurrence and length of the fibrils and nodules were dependent on the dose of gamma irradiation. More ripples were formed in the 2.5 Mrad and higher cups, compared to the non-irradiated cups (in-vitro and retrieved) . The in-vitro cups formed more ripples than the retrieved cups. In general, the SEM features for in-vitro Mrad cups appeared similar to those of the retrieved Mrad cups.
The in-vitro Mrad cups accurately reflected the conditions of the artificial joint in the living body. Therefore, comparisons of retrieved PE cups with simulator PE cups appeared to be a very powerful research tool. SEM observation demonstrated far less wear damage in the ECL cups than in the non-ECL PE. Thus the ECL PE cups appeared to be a significant improvement over conventional non-irradiated PE cups, in terms of wear resistance.
