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The impact of alendronate on the mechanical properties of cortical bone
DOI:10.1038/bonekey.2014.92
This group previously investigated how the mechanical properties of whole dog ribs changed during three years of alendronate therapy (0.2 and 1 mg/kg/day, vs. placebo). Here, they use histomorphometry to assess the fatigue resistance of rectangular cortical beams extracted from adjacent ribs of the same animals, which were subjected to fatigue loading with four-point bending at six distinct stress amplitudes.
The cortical beams from alendronate-treated dogs showed reductions in initial and final secant moduli and increases in modulus loss that correlated with drug dose. A reduced fatigue life was also observed but the trend was not significant for the lower dose, which corresponds most closely the human therapeutic dose.
The previously observed reductions in secant moduli and fatigue properties of samples from alendronate-treated animals were associated with increased microdamage in the form of extended crack length; this study also showed an association with reduced osteonal area and lacunar density.
Editor’s comment: This is a further warning that substantial suppression of bone turnover reduces bone toughness under monotonic loading and decreases fatigue life of compact bone tissue under cyclic loading. Microdamage increases interstitial area and crack length and persists due to a reduction of lacunar density and attenuated intra-cortical remodeling. This leads to reduced osteon diameter and length. Although significance was only reached at the highest dose of alendronate, long-term anti-resorptive treatment in osteoporotic patients could contribute to an increased risk of atypical cortical shaft fractures.
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