Abstract
We carried out SEM analysis on the surface of retrieved polyethylene cups in different stages of wear, to examine the wear process. Nineteen UHMWPE liners were retrieved at revision surgery (seventeen of H1900 resin irradiated by 2.5Mrad in air, two of RCH1000 resin irradiated by 2.5Mrad in air) . Implant period was from 3 months to 20.7 years (average 9.9 years) . The cups were classified into high-wear cups (wear rate: above 140mm3/year), intermediate-wear cups (wear rate: 80 to 140mm3/year) and low-wear cups (wear rate: below 80mm3/year) . The wear rates were measured by a fluid displacement method. The cups were studied by SEM.
Ripples mainly appeared on the low-wear cups; nodules and fibrils mainly appeared on the high-wear cups. Folding was observed on all cups, but folding with numerous fibrils was striking on the high-wear cups. The cup retrieved at 3 months already exhibited folding. From these results, the wear-response appeared to be a 3-step process, involving (1) first the formation of folds, (2) formation of surface ripples, and then (3) the toughness of the PE matrix in releasing a wear-fibril to form a debris particle. These retrieved-cup data will provide better understanding of competing PE wear mechanisms.
