Biokeramik für Anwendungen in der Orthopädie

Zirconia ceramics have several advantages over other ceramic materials, due to the transformation toughening mechanisms operating in their microstructure that can give to components made out of them, very interesting mechanical properties. The research on the use of zirconia ceramics as biomaterials started about twenty years ago, and now zirconia (Y-YZP) is in clinical use in THR, but developments are in progress for application in other medical devices. Recent developments have concentrated on the chemistry of precursors, in forming and sintering processes, and on surface finish of components. Today's main applications of zirconia ceramics is in THR ball heads. This review takes into account the main results achieved up to now, and is focused on the role that microstructural characteristics play on the TZP ceramics behaviour in ball heads, namely mechanical properties and their stability, wear of the UHMWPE paired to TZP, and their influence on biocompatibility.

The biocompatibility of alumina ceramic was tested by means of macrophage cultures, intraperitoneal (i.p.) and intramuscular (i.m.) application of powdered particles in rats, and by implantation of solid samples in the paravertebral muscles and the condylus femur. No acute cytotoxicity was found in macrophage cultures. The i.p. and i.m. application of powdered particles in the beginning showed a granulocytic reaction, later followed by a histiocytic reaction. Also, the morphological changes in the organs of reticulo histiocytic system (RHS) are shown. In the solid samples implantation, the fibrogenetic stimulus is measured by morphological analysis of the connective tissue membrane around the sample. The importance of the individual cell observation by transmission-electron microscope (TEM) examination is evidenced. The experimental results are compared to the environmental reaction of smaller animal-adapted prostheses and prostheses having been implanted in human patients. Good biocompatibility is confirmed by these investigations; also regarding central position of the macrophages, the environmental reaction due to implant material is shown.