Bioresorption of ceramic strontium-85-labeled calcium phosphate implants in dog femora. A pilot study to quantitate bioresorption of ceramic implants of hydroxyapatite and tricalcium orthophosphate in vivo.

Ceramic hydroxyapatite and tricalcium orthophosphate were radioactively labeled with their strontium-85 analogs. Porous blocks of these materials (dimensions 2.5 X 1.25 X 0.5 cm) were implanted into surgically created defects in dog femora. The fate of the implants was studied by roentgenography, radioactivity measurements, histology, and microradiography. The radioactivity over the implant site was followed for 22 weeks. Implants were retrieved after 20-25 and 50-55 weeks. Hydroxyapatite implants were not affected by biodegradation processes, while tricalcium orthophosphate implants were subject to extensive bioresorption (25%-30% in 22 weeks). Resorption debris from tricalcium orthophosphate implants was found in mononuclear phagocytes and multinuclear osteoclastlike cells. The supposition is that tricalcium orthophosphate is transformed into hydroxyapatite in a physiologic environment. Labeling of ceramic calcium phosphate implants with strontium-85 analogs offers an adequate technique to quantitate bioresorption in vivo.