Effects of radiation on the use of hydroxyapatite for orbital reconstruction in the rabbit

The gross and histopathologic effects of external beam radiation on host response to subperiosteal implantation of dense hydroxyapatite (HA) blocks along the superior orbital rim was investigated, using the rabbit as an experimental model. Three study groups were employed: those with no radiation, those receiving 500 cGy, and those receiving 1,500 cGy. The hydroxyapatite blocks were surgically implanted 2 weeks after administration of the radiation. The pathologic specimens, including the HA block and the neighboring bone segment, were harvested and examined at either the fourth or 12th postsurgical week. There was essentially no inflammatory reaction stimulated by the implanted HA blocks, nor was there any evidence of abnormal bone remodeling in the underlying orbital rim segments. The most secure bonding between the HA block and bone was found in the specimens having received either 500 cGy or 1,500 cGy and harvested at 12 weeks. We conclude that HA serves as an acceptable bone graft substitute in areas previously treated with radiation. The various properties of HA are also reviewed.