Bone Abstracts

Bone microarchitecture and material level properties independently contribute to the improvement of bone strength induced by strontium (Sr) ranelate treatment as evaluated by μCT-based finite element analysis. The influence of in vitro Sr exposure on material level properties and on bone mechanical properties is unknown.

We investigated whether in vitro exposure of rat femurs to Sr is able to modify the bone mechanical properties independently of geometrical changes. One femur was exposed overnight to 1 M Sr Cl solution and the controlateral to 1 M NaCl₂ solution. Then three point-bending tests were performed allowing the determination of maximal load, stiffness, and energy as well as post yield behaviors, i.e. post yield load and deflection characterizing plastic phase. Similar protocol was performed using 1 M CaCl solution to investigate the specificity of Sr. Bone material properties was evaluated using nanoindention. The total number of investigated bone samples was 32, significant differences were evaluated by student paired t-test.

The in vitro exposure to 1 M SrCl₂ solution increased significantly maximal load (+13%), energy (+30%) but not stiffness. In this model, modification of bone mass, geometry, or micro architecture could be excluded since exposure to Sr was performed in vitro. Modification of mechanical properties could thus only be attributed to modification of bone material level properties; which were all significantly increased by in vitro Sr exposure. Furthermore, parameters characterizing plastic deformation of the femur were markedly improved by Sr exposure: plastic energy (+76%) post yield load (+45%) and post yield deflection (+62%). Interestingly, these results are similar to those obtained by in vivo by Sr ranelate treatment. Exposure to CaCl₂ did not affect mechanical properties underlying the selectivity of the Sr effect.

These results further support the important role of bone material level properties as a determinant of bone strength.