Mechanical Behavior in Human Cortical Bone Across Multiple Length Scales: Investigations of Elastic Anisotropy and Damage Accumulation

Elastic properties and fatigue microdamage accumulation in human cortical bone both vary with age, disease, gender, and anatomic location, as governed by complex structure-property relationships across multiple length scales. Variability in experimental measurements of elastic constant magnitudes and anisotropy was shown to be governed primarily by the apatite crystal volume fraction and orientation distribution, respectively, using a specimen-specific, multi-scale micromechanical model. A subsequent multi-scale framework combining specimen-specific micromechanical and micro-finite element models showed that the apatite crystal orientation distribution accounts for the dominant overall transverse anisotropy, while the architecture of intracortical porosity accounts for more subtle variations in tissue orthotropy. Nondestructive and threedimensional detection of fatigue microdamage was recently enabled using contrast-enhanced micro-computed tomography. Damage initiation and accumulation was shown to be non-uniform, occurring in preferentially in regions of tissue experiencing elevated tensile principal strains due to the whole bone morphology, mode of loading, and intracortical porosity.