Improvement of polyethylene by irradiation in artificial joints

The decrease in socket thickness of several total hip prostheses was measured on X-ray film. The following prostheses were compared: (1) SOM “28 mm metal head and an ultra-high-molecular-weight-polyethylene (UHMWPE) socket irradiated with 10⁸ rad of γ-radiation”, (2) T-28 “28 mm metal head and a UHMWPE socket not irradiated”, (3) Bioceram “28 mm alumina head and UHMWPE not irradiated” and (4) irradiated Bioceram “28 mm alumina head and UHMWPE socket irradiated with 10⁸ rad of γ-radiation”.The average steady state wear rate of SOM, T-28, Bioceram and irradiated Bioceram were 0.076, 0.247, 0.098 and 0.072 mm/year, respectively.The weight bearing portion of the irradiated socket presented a clearly-outlined and irregular pattern of about 0.1 μm thickness having a smooth ripple surface. The scratch and holding phenomenon characteristics of non-irradiated sockets was not observed at all.In our experimental tests using an IS sliding wear test machine, the wear measured as decrease of thickness was smallest at 10⁸ rad, although there was an increase in the coefficient of friction. Our experimental and clinical findings suggest that the best total hip prosthesis at present is one with an alumina head and a UHMWPE socket irradiated with 10⁸ rad of γ-radiation.