The effects of irradiation and ageing on the abrasive wear resistance of ultra high molecular weight polyethylene

The wear of ultra high molecular weight polyethylene (UHMWPE) bearing components is of major concern in the context of the prolonged performance of total human joint replacements. Analysis of retrieved tibial components from knee prostheses shows that fatigue is the major cause of failure, but that wear is also often associated with abrasion mechanisms caused by bone cement and other debris entering the contact region. UHMWPE used in this application is commonly sterilised by gamma irradiation which results in material property changes via free radical formation and subsequent oxidative degradation. This paper investigates the effects of gamma irradiation dose in the range 0-10 Mrad, followed by post-irradiation ageing, on the abrasive wear resistance of plane UHMWPE specimens and also on retrieved tibial implant material using a micro-scale abrasion test. A significant decrease in wear resistance with increasing radiation dose and ageing was seen, which was correlated with changes at the molecular level as detected by differential scanning calorimetry.