A non-invasive in vitro technique for the three-dimensional quantification of microdamage in trabecular bone.

An accurate analysis and quantification of microdamage is critical to understand how microdamage affects the mechanics and biology of bone fragility. In this study we demonstrate the development and validation of a novel in vitro micro-computed tomography (microCT) method that employs lead-uranyl acetate as a radio-opaque contrast agent for automated quantification of microdamage in trabecular bone. Human trabecular bone cores were extracted from the femoral neck, scanned via microCT, loaded in unconfined compression to a range of apparent strains (0.5% to 2.25%), stained in lead-uranyl acetate, and subsequently re-scanned via microCT. An investigation of the regions containing microdamage using the backscatter mode of a scanning electron microscope (BSEM) showed that the lead-uranyl sulfide complex was an effective contrast agent for microdamage in bone. Damaged volume fraction (DV/BV), as determined by microCT, increased exponentially with respect to applied strains and proportionately to mechanically determined modulus reduction (p<0.001). Furthermore, the formation of microdamage was observed to occur before any apparent stiffness loss, suggesting that the localized tissue yielding occurs prior to the structural yielding of trabecular bone. This non-invasive in vitro technique for the detection of microdamage using microCT may serve as a valuable complement to existing morphometric analyses of bone.