BIOLOGICAL EFFECTS OF ALUMINUM DIFFUSION FROM PLASMA-SPRAYED ALUMINA COATINGS

Plasma-sprayed alumina (Al2O3) coatings on metal stems of hip prostheses are used to favour bone apposition on the stem without fibrous interposition. We tested both in vitro and in vivo in rabbits, alumina coatings in order to evaluate the biological effect of this material on bone. Mice fibroblasts were grown on Al2O3-coated discs and time course of aluminium concentration was recorded in two phosphate and citrate buffers (pH 4 and 7) bathing the alumina coated discs. Alumina-coated cylinders were implanted into femur condyles of ten rabbits for periods of time from 1-6 months. Then, they were histologically analysed using light and scanning electron microscopy, and X-ray microanalysis. Cell proliferation was not affected on alumina coatings compared to controls. In pH 4 buffer, aluminium was released from the coatings. From a period of implantation of 4-6 months an increasing demineralization process took place in the bone at the coating contact. Aurine staining showed the presence of aluminium at the interface between the non-mineralized and the mineralized bone. These results suggest that aluminium is released from alumina coatings and leads to bone demineralization at the coating contact.