Retrieval analyses of highly cross-linked polyethylene acetabular liners four and five years after implantation.

Two Durasul highly crosslinked polyethylene liners were exchanged during revision surgery four and five years after implantation, respectively. The retrieved liners were evaluated macroscopically and surface analysis was performed using optical and electron microscopy. A sample of each liner was used to determine the oxidation of the material by Fourier transform infrared spectroscopy. Samples of the capsule were examined histologically. The annual wear rate was found to be 0.010 and 0.015 mm/year, respectively. Surface analysis showed very little loss of material caused by wear. Histological evaluation revealed a continuous neosynovial lining with single multinucleated foreign-body giant cells. Our findings showed no unexpected patterns of wear on the articulating surfaces up to five years after implantation and no obvious failure of material.

In vivo tribological performance of 231 metal-on-metal hip articulations.

231 cobalt-chromium metal-on-metal (METASUL design) retrieved articulations (297 retrieved components) were examined for their in vivo wear behaviour. A running-in period of about one year is observed where the in vivo wear rate for the whole articulation is approximately 35 m/year. After this running-in period, the measured in vivo wear rate of the whole articulation decreases to about 5 m/year. The metal-on-metal articulation can be considered as a very low wear articulation system. The combination of the specially designed components is mandatory to assure this low wear behaviour. In case of a mismatched bearing (stainless steel head - cobalt-chromium inlay), large amount of wear was measured. (Hip International 2002; 2: 73-6).

Analysis of 118 second-generation metal-on-metal retrieved hip implants.

Osteolysis is due to particulate wear debris and is responsible for the long-term failure of total hip replacements. It has stimulated the development of alternative joint surfaces such as metal-on-metal or ceramic-on-ceramic implants. Since 1988 the second-generation metal-on-metal implant Metasul has been used in over 60 000 hips. Analysis of 118 retrieved specimens of the head or cup showed rates of wear of approximately 25 microm for the whole articulation per year in the first year, decreasing to about 5 microm per year after the third. Metal surfaces have a 'self-polishing' capacity. Scratches are worn out by further joint movement. Volumetric wear was decreased some 60-fold compared with that of metal-on-polyethylene implants, suggesting that second-generation metal-on-metal prostheses may considerably reduce osteolysis.