The biological performance of calcium phosphate ceramics in an infected implantation site: II. Biological evaluation of hydroxyapatite during short-term infection.

Macroporous hydroxyapatite was implanted submucosally in the rat middle ear and studied after intratympanic injection of a Staphylococcus aureus suspension. The middle ear infection was induced 1 week after the implantation, and the effects of infection on the middle ear and the implant material were evaluated after 1, 3, 7, and 14 days by light and electron microscopy. The findings in the infected middle ear with an implant corresponded well with those described for the infected middle ear cavity without an implant. The reactions of the tissue over the implant were similar to those of the original mucosa of the middle ear. Bone was deposited on the implant and in its pores in relatively large quantities. Biodegradation, due at least partially to phagocytic activity of macrophages and multinucleated cells, was more prominent than previously found. This higher degree of biodegradation may be attributed to the use of the mucosal implantation technique, because this was the only point of divergence with respect to material or methods from earlier work reported by our group. The present results, together with those published earlier, suggest that this material has promising features for use as a bone substitute in reconstructive middle ear surgery. Definitive conclusions on biological performance and biofunctionality will, however, have to await long term clinical trials.