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.

Introduction: Irradiation crosslinking of UHMWPE has been developed as an improvement over conventional UHMWPE to provide improved wear resistance, demonstrated during in-vitro studies as well as in early clinical results [1, 2]. The analysis of explants made of highly crosslinked UHMWPE yields valuable information about their clinical utility.

Material: 26 explanted highly crosslinked UHMWPE inlays (Durasul, Zimmer) from various sources were surgically retrieved and analyzed. All inlays articulated with 28 mm CoCr heads except one (32 mm) and had an implantation time from 3 to 43 months (mean 14 months). The reasons for revision were: 9 for infection, 2 for ossification, 4 for luxation, 2 for pain, 4 for bone fracture and 5 for aseptic loosening.

Results: On all explants, scratches on the articulation area as well as machining marks were visible; the latter have sometimes been smoothed out in the loaded area. There were no signs of delamination or oxidation. The loaded area, analyzed by SEM, exhibits microscopic changes in the morphology which have been reported to be potential microcracks [3]. When analyzed by TEM, it was seen that these surface features are ripples and folds, which are induced by normal adhesive-abrasive wear behavior and have a maximum size of 5 m [4]. Mechanisms like folding are reported also from conventional UHMWPE [5]. In order to separate wear from deformation, the shape memory behavior of UHMWPE was employed. After thermal treatment, smoothed machining marks were observed to recover. After about two years in-vivo, some of the machining marks in the loaded area do not recover, which indicates that minimal wear in the range of the height of the machining marks (approx. 10 m) has occurred. In comparison, after this time, 200–600 m of wear would be expected for conventional UHMWPE [6].

Conclusions: The findings from the retrievals showed that there is no adverse wear or material failures due to delamination or cracks at 3 to 43 months. The accumulated scratches are due to the fact that the wear of this highly crosslinked polyethylene is very small. The scratches do not polish out over time as with conventional UHMWPE and do not show adverse effects on the long-term behaviour of the implant. These results are consistent with the performed in-vitro studies.

Aims: To solve the major problems of osteolysis due to particle debris in total hip arthroplasty, highly cross-linked UHMWPE were developed. Investigations on early retrieved components of Durasul™ (Centerpulse Orthopedics Ltd.) provide the opportunity to evaluate the highly crosslinked components for wear damage or other effects on the material. Methods: 12 Durasul™ alpha cups were surgically retrieved and analyzed. The range of in-vivo duration of the cups was between 3 and 15 months. The reasons for revision were not related to material failure. The investigations were made by microscopy and CMM measurement. To differentiate between creep and wear, the memory effect was used. Results: In the articulation, machining marks look partly flattened, or show a highly scratched surface. The loaded area shows some microscopic changes of the morphology like ripples and folds, which are shear-induced ripple formations and material overlappings. In some cases the retrieved cups show a yellow discoloration, indicating the in-vivo absorption of synovial liquid proteins. Conclusion: The findings from the retrievals showed that there is no adverse wear at 3–15 months and there were no material failures due to wear, delamination or cracks. All the effects are accumulating on the articulating surface and lead to the dull scratched morphology. Mechanisms like material overlapping and yellowing are reported also from conventional UHMWPE and do not show adverse effects on the long-term behaviour of the material.

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 μm for the whole articulation per year in the first year, decreasing to about 5 μm 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.