Microstructural heterogeneity and the fracture toughness of bone

Age-related changes in the skeleton often lead to an increase in the suscep tibility of bone to fracture. The purpose of this study was to determine wh ether differences in material properties between the osteonal and interstit ial regions of bone have an effect on bone fracture properties. Parameters such as longitudinal fracture toughness, transverse fracture toughness, por osity, interstitial microhardness, osteonal microhardness, bone density, an d weight fractions of the mineral and organic phases of bone were examined as a function of age using female baboon femurs. With increasing age, the l ongitudinal fracture toughness decreased significantly as did transverse fr acture toughness, whereas the interstitial microhardness increased. However , no significant differences in the other parameters were observed as a fun ction of age. Using the ratio of interstitial microhardness to osteonal mic rohardness as a measure of the differences in the material properties in th ese two regions, correlation analysis revealed that the longitudinal fractu re toughness of bone has a significant correlation with the microhardness r atio. Localized differences in material properties between osteonal and int erstitial regions of bone increase with age; such differences may result in high stress concentrations at cement lines and facilitate longitudinal cra ck propagation. (C) 2000 John Wiley & Sons, Inc.