Bone Abstracts

Although the fracture risk reduction under bisphosphonate treatment in osteoporosis is clinically well established, it remains understudied why the efficacy of bisphosphonate therapy is higher for the prevention of vertebral fractures compared to other fractures.

Our aim was to investigate whether anti-resorptive therapy with alendronate would result in different regional variations of structural indices in the vertebral body. We investigated the microstructure of L3 vertebrae from 14 women (mean age 83 years) with high-resolution peripheral quantitative CT (82 μm). Further, we scanned cylindrical samples from the anterior and posterior vertebrae with micro-computed tomography at 3.5 μm resolution and determined their mechanical competence with uniaxial compression testing.

The CT results showed a significantly higher average bone volume to tissue volume ratio (BV/TV), T-Score, and trabecular thickness for the alendronate treated group compared to the osteoporotic control group. Regression analysis showed a high influence of BV/TV on the maximum force for both groups.

While our results for the regional structural indices in the osteoporosis group agree well with epidemiological data, we found specific deviations in regional structures for the alendronate group. The osteoporosis group had a significantly lower BV/TV and trabecular number in the anterior regions compared to the posterior ones. In contrast, the alendronate group did not exhibit these regional differences. Further, trabecular thickness was higher for the anterior cylinders from the alendronate group than those from the osteoporosis group.

Alendronate therapy influences the regional variation (anterior vs posterior) of vertebral BV/TV in comparison to treatment naïve controls. Contrary to osteoporotic bone this study shows a uniform distribution of bone volume in anterior and posterior regions for alendronate treated bone. This uniform distribution might make the elderly vertebrae less susceptible to wedge fractures. Therefore, our study provides insight in the higher fracture risk reduction in vertebrae compared with other fracture sites.