THE ASSOCIATION BETWEEN RATES OF WEAR IN RETRIEVED ACETABULAR COMPONENTS AND THE RADIUS OF THE FEMORAL-HEAD

Current evidence suggests that loosening of the acetabular socket is r elated to the volume of ultra-high molecular weight polyethylene wear debris generated at the articulating surfaces, through a process of bo ne resorption. Therefore it is important that the rate of volumetric w ear is minimized in an attempt to extend the useful life of the proced ure. Laboratory evidence indicates that a reduction in sliding distanc e would be beneficial in achieving this target and may be attained by a reduction in femoral head radius. To investigate the relationship be tween femoral head size and the rates of both volumetric wear and pene tration, 200 acetabular components were retrieved at the time of revis ion surgery. The joints had femoral heads ranging in size from 11.1 to 19.8 mm radius. For those sockets that were loose at revision surgery , a significant correlation was observed between the rate of volumetri c wear and the radius of the femoral head. For this cohort an increase in radius of 1 mm resulted in an increased rate of volumetric wear of 5.1 (SE 1.4) mm(3)/yr. However, the explained variance in the regress ion was low and exemplifies the multifactorial nature of the wear proc ess. In particular, it is anticipated that the activity of the patient will have a significant effect on the rate at which the debris is pro duced. No significant correlation was observed between the rate of lin ear wear and femoral head radius. These results would indicate a benef it in using head sizes of a smaller radius, which generate debris at a reduced rate, and therefore require more time to accumulate large vol umes of wear products.