Statistical Analysis of Surface and Sub-Surface Residual Stress Fields in Retrieved Alumina Femoral Heads after Long-Term Implantation
The surface of retrieved alumina (Al2O3) femoral heads was investigated by piezo-spectroscopic techniques based on confocal photo-stimulated fluorescence. The micrometric spatial resolution of the laser beam impinging on the investigated joint surface (typically about 1 $m in lateral resolution) enabled us estimating patterns and magnitude of residual stress in extremely narrow zones, at least comparable with the grain size of the material. According to a statistical collection of data on a microscopic level, it was possible to assess the retrieved femoral heads in-toto, thus extending the microscopic analysis to the entire surface of the joint. A stress field was found, which mainly arose from loading history, and displacements acting on the femoral head during its lifetime. Residual stress data enabled us to draw interesting conclusions about the role of the material microstructure and the peculiar kinetic mechanisms involved with the use of the joint. Spectroscopic techniques, which are complementary to in vitro testing procedures and theoretical stress analyses based on finite-element methods, can be very useful in improving the design of the femoral head and in optimizing the microstructural characteristics of the ceramic materials employed.
Takashi Nakamura, Kimihiro Yamashita and Masashi Neo
T. Tateiwa et al., "Statistical Analysis of Surface and Sub-Surface Residual Stress Fields in Retrieved Alumina Femoral Heads after Long-Term Implantation ", Key Engineering Materials, Vols. 309-311, pp. 1251-1256, 2006