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Research into new surface coatings and surface processing methods for prostheses is subject to numerous studies. The aim of this study was to test an innovative biomechanical measuring method for the examination of the ingrowth of bone implants. Using a transcortical model, coated (n=14) or uncoated (n=14) titanic cylinders were implanted into the lateral condyle of 28 New Zealand White Rabbits. After 6 weeks or 6 months the animals were sacrificed and the osseointegration of the implants was evaluated biomechanically and histologically. Up to traction of 50 N the load dependent movement between bone and testing cylinder did not lead to a destruction of the bone-implant-interface. Therefore, biomechanical and histological investigations could be performed in the same specimen. The results of both evaluations showed a significant correlation (correlation coefficient -0.79; p < 0.01) and were absolutely reproducible. With the method of non-destructive mechanical testing, it is possible to halve the number of required animals. Additionally, the results of the biomechanical and histological analysis can be compared and thus serve as an internal control. In summary, the method of non-destructive mechanical testing represents an ideal tool to study new surface coatings and surface processing methods for prostheses.

Aim: Most methods used for the determination of volumetric wear of polyethylene cups are based on the assumption that the head of the prosthesis penetrates the cup in "cylindrical" fashion. The new accurate optical method is independent of this disputable assumption., Method: The articulating surface of the cup is scanned with light and a data set of 60,000 pixels obtained in this way is stored in a computer. Data obtained from used cups were compared with those obtained from unused cups. The volumetric wear was calculated directly by threefold integration. To assess the changes in surface shape, the data are fitted by an ellipsoid whose long axis defines the mean direction of load. A total of 18 retrieved and 3 unused cups of different types were studied., Results: The unused acetabular cups deviated only slightly from ideal hemispheres. The surfaces showed rotational symmetry, and an undulation having an amplitude of 0.1 mm between dome and equator. For all explanted cups, the assumption of cylindrical penetration of the head into the polyethylene was shown not to represent the true situation. The cup expands in all directions, and the volumetric wear is underestimated by 50% with the traditional methods. The data suggest that long-term survival may be jeopardized when the main direction of loading is centered on the dome of the cup. Ceramic heads were associated with smaller rates of volumetric wear., Conclusion: The new optical method is characterised by short measuring times, precision and simple application. Analysis of the wear patterns of polyethylene components using this technique may contribute to a further understanding of the complex mechanisms of aseptic loosening.