Administration of PTH and ibandronate increases ovariectomized rat compact bone viscoelasticity

In this study, the bone mineral density (BMD), geometry, macroscopic viscoelastic properties and mechanical strength in five different groups of Sprague-Dawley rats (sham operated, ovariectomized with vehicle, parathyroid hormone and/or ibandronate administration) were examined by peripheral quantitative computed tomography (pQCT), dynamic mechanical analysis (DMA) and three-point bending test. At the end of the study, storage modulus (E'), loss tangent (tanδ), ultimate force (F_u) and stiffness (S) had greatly decreased in vehicle-treated ovariectomized group as compared to sham group (p<0.05). The concurrent administration of parathyroid hormone and ibandronate group exhibited the largest cortical area (Ct.Ar) and thickness (Ct.Th), E', tanδ (0.3Hz) and subsequently highest F_u as compared to the mono-therapy groups (p<0.05). However, significant changes were not observed in the BMD values of different groups (p>0.05). The relationships between these potential predictors of bone strength (E', tanδ, BMD and Ct.Ar) and bone mechanical strength parameters (F_u, S and ultimate stress σ_u) were also examined. Interestingly, during normal daily activity frequency range (0.9-6Hz), tanδ and F_u were positively correlated. Taken together, these data suggest that DMA can serve as an effective tool to assess bone strength which would be ignored under the normal clinical screenings due to an unchanged BMD. DMA can therefore be used as a better tool to assess the osteoporotic drug efficacy.