The biomechanical response of human bone: the influence of bone volume and mineral density

The purpose of this study was to investigate the relationship between bone mineral density and the biomechanical response. This study presents results from 117 human rib cortical bone coupon tests from six cadavers, three male and three female, ranging in age from 18 to 67 years old. First, the material properties of human rib cortical bone were determined using dynamic tension coupon testing. The rib sections were taken from the anterior, lateral, and posterior regions on ribs 1 through 12 of each cadaver's rib cage. The cortical bone was isolated from each rib section with a low speed diamond saw, and milled into dog bone shaped tension coupons using a small computer numerical control machine. A high-rate servohydraulic Material Testing System equipped with a custom slack adaptor, to provide constant strain rates, was used to apply tension loads to failure at an average rate of 0.5 strains/sec. The elastic modulus, yield stress, yield strain, ultimate stress, ultimate strain, and strain energy density were determined from the resulting stress versus strain curves. Second, two measures of bone mineral density (BMD) were determined: the global BMD of each cadaver through standard radiographic scaling, and the percent mineralization of each coupon through ash analysis. Overall, the global BMD was correlated with the biomechanical properties, but the local apparent density was not. The global BMD is actually a surrogate for the volume of bone present and it is highly correlated with subject age. In contrast, the apparent density is the true local BMD and it was not correlated with subject age. This is consistent with previous research and illustrates that the overall structural biomechanics of bone are related to the volume of bone, or global BMD, while they are much less related to the apparent density, or local BMD, which varies much less with age.