WEAR POLYETHYLENE CUPS IN TOTAL HIP-ARTHROPLASTY - A STUDY OF SPECIMENS RETRIEVED POST-MORTEM

The wear of polyethylene components of total hip replacements has prev iously been studied radiographically and by analysis of retrieved comp onents, The extent of wear, however, has largely been determined from components retrieved at reoperation and has therefore been based on a subset of patients in whom the prosthesis is more likely to show exces sive wear, The study of cups retrieved post mortem provides a better i ndication of the extent of wear of well functioning components, Twenty -six polyethylene liners were retrieved at autopsy from nineteen patie nts, after a mean of ninety-one months (range, thirty-three to 206 mon ths) in situ, Each component had articulated with a thirty-two-millime ter-diameter femoral head, The components were evaluated visually for evidence of polyethylene wear such as pitting, scratching, and burnish ing, Additionally: a shadowgraph technique was used to examine molds o f the inner surface of the liner to determine the direction and extent of wear, The mean extent of linear wear of the retrieved liners was 0 .45 millimeter (range, 0.17 to 1.07 millimeters), and the mean rate of wear was 0.07 millimeter (range, 0.02 to 0.18 millimeter) per year, T he mean volumetric wear was 245.3 cubic millimeters (range, 13.0 to 77 9.1 cubic millimeters), and the mean rate of volumetric wear was 39.8 cubic millimeters (range, 1.0 to 131.3 cubic millimeters) per year, Th e mean rate of wear for the twenty-six liners was 45 to 69 per cent le ss than the rates reported in the literature for polyethylene liners r etrieved at reoperation, Examination of the articulating surface did n ot reveal gross evidence of surface failure such as delamination or fa tigue cracks, In general, the surfaces were merely burnished and scrat ched, The rates of wear of press-fit, metal-backed liners were signifi cantly higher than those of all-polyethylene cemented components (p < 0.05), Additionally, statistical analysis revealed no correlation betw een wear and the patient's age, weight, or gender; the duration of imp lantation; or the thickness of the polyethylene, These results indicat e that wear of the polyethylene of well functioning hip replacements i s not as excessive as reported previously.