Integration of dense HA rods into cortical bone.

HA ceramics are daily used in human surgery for bone healing partly due to their ability to integrate into bone. They are generally used under a macroporous form. The behaviour of dense HA after implantation is not so well known. We implanted within cortical sheep femurs dense pure HA-ceramics cylinders for periods from 2 weeks to 18 months. The samples were then sectioned and examined using back-scattered and secondary SEM and the interface was analysed using EDS. Histomorphometry measurement was also performed using an image analysis device coupled to a light microscope. It appeared that the cylinders were in direct contact with immature bone after three weeks. The bone maturated within three months. The implant surface showed moderate signs of resorption and some grains were released from the surface. The resorption zone was only a few microm thick after 18 months. The bulk ceramic contained default zones of increased porosity. They can constitute fragile zone when located close to the surface in which the resorption rate is increased. We conclude that dense pure HA is poorly degraded when implanted in cortical bone. Degradation depends on the defaults found on the ceramic structure and the remodelling of bone surrounding the material.