EFFECT OF FEMORAL-HEAD SURFACE-ROUGHNESS ON THE WEAR OF ULTRAHIGH MOLECULAR-WEIGHT POLYETHYLENE ACETABULAR CUPS

We studied the effect of femoral head surface roughness on the wear of ultrahigh molecular weight polyethylene (UHMWPE) acetabular cups usin g a hip joint simulator and a reciprocating wear tester. Compared with the hip simulator, the reciprocating wear tester severely exaggerates the effect of counterface roughness on UHMWPE wear and drastically un derestimates the wear rate of the UHMWPE against smooth undamaged coun terfaces. According to the hip simulator test results, the wear rate o f the UHMWPE cups is approximately proportional to the square root of the femoral head roughness R-a (center-line-average roughness) rather than to R-a raised to a power greater than one as predicted by pin-on- disk studies. Roughening of the femoral heads by an order of magnitude results in a 2- to 3-fold increase in the wear rate. Therefore, the m uch wider clinical variations of wear cannot be fully explained by var iations in surface roughness of the femoral heads.