Strontium Ranelate Treatment Improves Trabecular and Cortical Intrinsic Bone Tissue Quality, a Determinant of Bone Strength

Beside its influence on determinants of bone strength (geometry, microarchitecture), which is likely to be related to a cellular effect, strontium ranelate improves bone tissue quality as evaluated by nanoindentation, increasing elastic modulus, hardness, and dissipated energy in vertebrae of rats treated for 104 wk with daily dose from 0 to 900 mg/kg. Introduction: We previously showed that strontium ranelate treatment improves the mechanical properties of the vertebral body and long bone midshaft in intact rats. The increased energy to failure obtained with strontium ranelate is essentially caused by an increase in plastic energy, suggesting that bone formed during treatment can withstand greater deformation before fracture. In the bone mineral phase, strontium is mainly located in the hydrated shell and could thus potentially influence intrinsic bone tissue quality. Materials and Methods: To study whether strontium ranelate treatment could positively influence intrinsic bone tissue quality (elastic modulus, hardness, and dissipated energy), nanoindentation tests were performed at the level of trabecular nodes and cortex under physiological or dry conditions in vertebrae of rats treated for 104 wk with strontium ranelate at a daily dose of 0, 225, 450, or 900 mg/kg (n = 12 per group). Ex vivo μCT measurements and axial compression tests of adjacent vertebral bodies were also performed. Significance of difference was evaluated using ANOVA. Results: In agreement with previous results, strontium ranelate (900 mg/kg/d) significantly increased versus controls in maximal load (+23%), total energy (+71%), and plastic energy (+143%). At the level of trabecular bone, strontium ranelate treatment resulted in a significant increase in elastic modulus (+15.1%, p < 0.01), hardness (+11.5%, p < 0.05), and dissipated energy (+16.2%, p < 0.001) versus controls in physiological, but not in dry, conditions. The effect was less pronounced in cortex. Conclusions: These results show for the first time a direct action of strontium ranelate on bone tissue quality. Beside its shown influence on classical determinants of bone strength (geometry, microarchitecture), which is likely to be related to a cellular effect, strontium ranelate improves bone tissue quality. This could contribute to the increase in bone strength and thus be involved in the reduction of fracture risk in postmenopausal osteoporotic patients treated with strontium ranelate.