Preliminary study of the effect of aging following irradiation on the wear of ultrahigh-molecular-weight polyethylene (original) (raw)

1995, Journal of Arthroplasty

Several studies have indicated that degradation of ultrahigh-molecularweight polyethylene following gamma irradiation in air adversely affects the mechanical properties of the material; however, it is not known how this subsequently affects its wear rate. Wear studies have therefore been performed on three groups of ultrahigh-molecular-weight polyethylene: unirradiated material, recently irradiated material (aged for 2 months), and aged irradiated material (aged for 5 years). The aging took place in sterile packaging on the shelf. The wear studies were carried out on a tri-pin-on-disk wear tester, with a pin from each type of material being studied in each test. In each test the wear rate of the nonirradiated material was slightly lower than the 2-month-aged, irradiated material. The 5-year-aged, irradiated material had the highest wear rate, and this was significantly greater than that of the unirradiated material (P < .05). low wear rates in vivo have been quoted, 3 in general volumetric wear rates in vivo are much higher, with average values for acetabular cups estimated to be in the range 40 to 90 mm3/y. 4 It is recognized that in the body, femoral counterfaces that are initially very smooth can become damaged by bone-cement particles, bone particles, metallic debris from stems, and hydroxyapatite partides. These roughened counterfaces can then cause large increases in the wear rate of UHMWPE. 2 The effect of deterioration of the counterface on increased wear of UHMWPE has been well documented. In contrast, the effect of degradation of UI-IMWPE on wear has received less attention. Clinical wear takes place over much longer periods compared with "accelerated" laboratory tests, and there is increasing concern about the degradation and aging of UHMWPE following gamma irradiation, 5 with oxidative degradation affecting both density and