Analysis of products diffused into UHMWPE prosthetic components in vivo.

Ten UHMWPE hip inserts, five ethylene oxide and five gamma-ray sterilised in air, were retrieved during surgical revision after aseptic failure. Time in situ varied from 6 to 23 years. First implant was carried out for degenerative arthritis in all cases. The retrieved inserts were cut into two parts perpendicular to the articulate surface and a series of 150 microm thick slices were obtained from the cross-section. These were studied by FTIR microscopy and the absorbed products were extracted with cyclohexane for identification by GC/MS and Py/GC/MS. All retrieved UHMWPE components, independent of the sterilisation method, showed species adsorbed on the surface, which were mainly synovial liquid protein components. In addition, species such as cholesterol, fatty esters of cholesterol and squalene, also originating from synovial liquid, were found in the bulk. The concentration of the different species varies depending on the individual patient.