Long-term wear of HIPed alumina on alumina bearings for THR under microseparation conditions

The long term wear and wear debris generated in HIPed alumina on alumina be arings for hip prostheses with microseparation in vitro is compared to stan dard simulator conditions and ex vivo specimens. Microseparation studies we re completed to five million cycles at two severity levels in attempts to r igorously evaluate the long-term tribological performance of the bearings. During the first million cycles (bedding-in) of the microseparation tests c haracteristic stripe wear was observed on all of the femoral heads with a m atching area on the rim of the acetabular inserts. Under mild microseparati on conditions an average wear rate of 0.55 mm(3)/million cycles was observe d during the initial million cycles which reduced to a steady state level o f 0.1 mm(3)/million cycles. Under more severe conditions an average wear ra te of 4.0 mm(3)/million cycles was observed during bedding-in which reduced to a steady state level of 1.3 mm(3)/million cycles. These compare to a be dding-in wear rate of 0.11 mm(3)/million cycles and steady-state wear rate of 0.05 mm(3)/million cycles for the same material under normal simulation with no microseparation. Furthermore, under microseparation the wear mechan isms and wear debris were similar to those observed in previous alumina ret rieval studies with debris ranging from 10 nm to 1 mum in size. (C) 2001 Kl uwer Academic Publishers.