Surface degradation of UHMWPe is recognized as a leading clinical concern, limiting the long-term performance in total knee replacements. Eight retrieved tibial plateaux and six wear screening test samples were evaluated for surface degradation features and microstructural features. The surface degradation features were assessed using stereomicroscopy and scanning electron microscopy. Microstructural features were evaluated using optical microscopy of thin cross-sections and a permanganate etching technique. The pitting mechanism of wear was observed on all eight retrieved TKR and covered an average of 12.6% of the surface area. The size of the pits were similar to the size of grains observed in the microstructural evaluation - approximately 100 to 200 microm. The presented observations of pitting in retrieved knee implants have shown that the post-processing microstructure may influence this mechanism of surface degradation and hence the wear products.

Wear of orthopaedic bearing materials, especially the ultra high molecular weight polyethylene (UHMWPe) component, is a leading clinical concern. The reported wear rates of typical bearing materials are subject to extreme variability due to various factors including the operating environment, measuring technique, testing protocol, and machine characteristics such as mechanical stiffness and vibration. Also, a lack of standardization in reporting pertinent information confounds this variability. This investigation characterized the performance of a wear testing device. Through vibrational analysis, an attempt was made to identify possible reasons for discrepancies in the reported wear testing results for orthopaedic biomaterials. Wear result variability was probably a combination of the vibration characteristics of the individual tester and uncertainties introduced by the wear measurements themselves. The effect of superimposed base vibrations on the pins was investigated. Characteristic frequencies of pin vibrations were linked to the dominant wear mechanisms in the orthopaedic tribological system.