THE EFFECTS OF IRRADIATION AND AGING 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 perform ance of total human joint replacements. Analysis of retrieved tibial c omponents from knee prostheses shows that fatigue is the major cause o f failure, but that wear is also often associated with abrasion mechan isms caused by bone cement and other debris entering the contact regio n. UHMWPE used in this application is commonly sterilised by gamma irr adiation which results in material property changes via free radical f ormation and subsequent oxidative degradation. This paper investigates the effects of gamma irradiation dose in the range 0-10 Mrad, followe d 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 correla ted with changes at the molecular level as detected by differential sc anning calorimetry.