Bone stiffness predicts strength similarly for human vertebral cancellous bone in compression and for cortical bone in tension

The yield strength and ultimate strength of cortical and cancellous bone tissue are very highly correlated to bone stiffness. For samples of human vertebral cancellous bone in compression and for bovine cortical bone in tension, the coefficient of determination (r 2) for regression between ultimate strength and stiffness was 0.89 and 0.92, and between yield strength and stiffness it was 0.94 and 0.93, respectively. The slope of the regression for human vertebral cancellous bone ultimate strength predicted by stiffness was not statistically different from similar regressions for cortical bone in tension in either a bovine sample or in published data from multiple species. We believe that the observed correlation results from the evolutionary need to build sufficiently strong bones using cells that are sensitive to deformation and that directly control bone stiffness, but not strength. The practical significance of this work is that an in vivo estimate of bone stiffness (e.g., from ultrasound measurement) may be a surrogate for bone strength.