An autoradiographic study of calcium phosphate ceramic bone implants in turkeys

Sintered, porous cylinders of beta-tricalcium phosphate ceramic (TCP) and hydroxyapatite (HAP) labeled with 45Ca were implanted into turkey ulnae for up to six months. Histologic examination of ground sections revealed extensive bone remodeling in the defect regions and resorption of both TCP and HAP. Autoradiograms suggest time- and composition-dependent events. Initial release of calcium ions was observed from both ceramics into adjacent new bone. Diffusion of calcium from TCP, but not HAP, extended into original bone at later periods. At six months, however, calcium from HAP was located intracellularly and within channels of distribution in hard tissue, away from the implant site. These data suggest that physical processes dominate initial HAP resorption while biologic (cellular) mechanisms become more significant later.