A study of the wear resistance of three types of clinically applied UHMWPE for total replacement hip prostheses.

Ultra high molecular weight polyethylene (UHMWPE) is routinely used as one half of a bearing couple in clinical orthopaedic applications. This material is generally one of two grades, compression moulded GUR 1120, with a molecular weight of 4.4x 10(6) g mol(-1), or ram extruded GUR 4150HP with a molecular weight of 7.3x10(6) g mol(-1) although other grades are used as well. This study examines the effect of molecular weight and processing method by comparing the wear resistance of these two materials together with a non-standard extruded form of GUR 1120. Wear studies have been conducted against counterface surfaces which represent new and scratch-damaged femoral heads with bovine serum lubricant in a uniaxial reciprocating test configuration. No difference in the wear resistance was found between any material when tested against smooth cobalt chrome counterfaces. On rough cobalt chrome counterfaces, although no statistically significant difference (P>0.05) was found between the extruded and compression moulded GUR 1120, the extruded GUR 4150HP had a consistently better wear resistance. These results are discussed with reference to previous wear studies as well as the physical and mechanical properties of these materials.