Tissue response to porous hydroxyapatite ceramic in the human femoral head.

We describe pathohistological findings of the human femoral head after it was grafted with hydroxyapatite (HA) and allogenic bone. The femoral head was removed because of the recurrence of a giant cell tumor 15 months after the graft. Histological investigation revealed that the entire surface of the HA granules was completely surrounded by the bone in the periphery of the grafted area; in some areas granules were partly in contact with the existing bone, and the rest were surrounded by fibrous tissue. There was no intervening layer of fibrous tissue between the granule surface and the bone where they were in direct contact. Pores were completely filled with fibrous tissue, partially filled with bone in the periphery of the pores, or completely filled with bone. Undecalcified histology revealed the formation of osteoid and ossification at the site where fibrous tissue infiltrated the pores. These findings indicated continued ingrowth of new bone into the HA pores. Under a scanning electron microscope, the surfaces of the granules showed clear demarcation in vitro, but it became less smooth, indicating in vivo changes. Although no foreign body reaction to the HA was noted anywhere, the HA surface appeared to be subject to a biodegradation process.