Aim: This study compares the effect of bisphosphonate and intermittent PTH administration on haversian remodeling in cortical bone allografts in rabbits. Materials and methods: An intercalary heat-treated cortical bone allograft was applied to a segment skeletal defect in the left femur of Japanese white rabbits. The rabbits were randomly assigned to one of three groups: the vehicle control group (CNT); the bisphosphonate group (B group); and the intermittent PTH treatment group (P group). Periodic radiographic evaluation was performed and peripheral quantitative computerized tomography (pQCT) was used to evaluate the total bone area (Area), bone mineral density (BMD), and bone mineral content (BMC). The allografts also underwent histological examination. Results: The P group was radiographically superior in the latter stage, compared with the other groups. pQCT analysis of the allografts showed that the B group had a significantly higher Area and BMC. These parameters in the latter stage were significantly lower in the P group than in the other groups. The allograft of the B group was histologically mostly necrotic bone, whereas allograft of the P group showed abundant newly formed bone. Conclusion: In rabbits, bisphosphonate prevents resorption, but suppresses remodeling and incorporation; by contrast, PTH increases resorption and accelerates allograft remodeling and incorporation. Based on our preliminary data, we suggest that further research on the manner of administration of bisphosphonate and PTH - which have contrasting effects - can be beneficial in maintaining bone strength and in regulating remodeling and allograft incorporation.
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