Recently, hydroxyapatite (H. A.) has often been used to reconstruct the bony defect in middle ear surgery. We used H. A. in 30 clinical cases: in 10 cases to reconstruct the posterior canal, in 16 cases (6 cases overlap with others) to obliterate the mastoid cavity, and in 10 cases to separate the mastoid and the attic. In 3 cases H. A. was later removed because infection, which led to circulatory failure in the skin over the mastoid. The other 27 are contented with H. A. Thus H. A. seems to be useful as a middle ear implant.
To evaluate the safety of H. A, we embedded it in a hole drilled in the bullae of adult guinea pigs. One month later, these animals were sacrificed under ether anesthesia, and the bullae were examined histologically by light microscope.
1) The embedded H. A. was tightly surrounded by soft tissue, in which no giant cells were observed. Therefore, it seems that no foreign body reaction occurred.
2) There was no evidence of bone formation on any surface of the embedded H. A., but bone induction was accelerated by H. A..