Effects of teriparatide on bone formation in novel unidirectional porous beta-tricalcium phosphate

This study aimed to evaluate the effect of intermittent teriparatide treatment on changes in bone formation using unidirectional porous beta-tricalcium phosphate in a rabbit bone defect model. Twelve Japanese white rabbits were used in this study. A 5 × 8 mm² rectangular area of periosteum was resected, followed by preparation of a cortical bone defect in a 4.5 × 7 mm² rectangular area using a high-speed bur. Unidirectional porous beta-tricalcium phosphate was embedded in the defect in the direction of the pores, parallel to the axis of the tibia. Six rabbits in the teriparatide group were subcutaneously injected with 30 μg/kg of chemically synthesized teriparatide three times per week starting on the day of the operation, while six rabbits in the control group were injected with a hormone stock solution according to the same schedule. Tissue samples were harvested at six weeks after implantation. Newly formed bone was observed as a green area after using Villanueva–Goldner stain on sagittal sections. A region of interest with a height of 3 mm and width of 5 mm was set in the center of the artificial bone. A portion of the new bone in the region of interest was extracted using analysis software (BZ-X analyzer; Keyence, Japan), and the area ratio of the newly formed bone was calculated by dividing the area of the extracted portion by the area of the region of interest. As seen with sagittal Villanueva–Goldner staining, the percentage of new bone area in the region of interest was significantly larger in the teriparatide group (33 ± 9.0%) than in the control group (24 ± 3.9%). Unidirectional porous beta-tricalcium phosphate used alone sufficiently resulted in new bone formation, but as combined use of teriparatide further enhances new bone formation, promotion of bone fusion can be expected, leading to better clinical outcomes when applied to surgical procedures in real-world settings.