Measurement and Analysis of Microdamage in Bone

Microdamage is an important aspect to assess bone quality. The objectives of this dissertation were to study the interaction between microdamage accumulation and different loading modes, and to observe microdamage in three dimensions.

A method for accurate preparation of cylindrical trabecular bone specimens was developed. The current level of on-axis accuracy using this technique could translate to an estimated average error of less than 5% in modulus measurements. The specimens were damaged by overloading in compression followed by torsion. Sequential staining technique was used to label microdamage due to the different load modes. Nearly 40% of the microcracks due to torsion propagated from the pre-existing microcracks caused by axial compression, indicating that existing microcracks may extend at relatively low strain if the loading mode changes. A second group of specimens was tested with torsion followed by compression. The microcrack density and diffuse damage area due to torsional overloading increased with shear strain level while the mean microcrack length was independent of shear strain level, indicating that the applied strain tended to initiate new microcracks rather than extending the existing ones. Over 20% of the microcracks formed in the initial torsional overloading propagated. The propagating microcracks were longer than microcracks from a single load measured in our own and other studies.

A new technique was developed to non-invasively observe microdamage in three dimensions using micro-CT imaging. Barium sulfate, used as the radio-opaque contrast agent to label microdamage in bone, had partial volume effects on adjacent bone tissue in micro-CT images. Four-point bending of double-notched beams was used to generate microdamage in a specific region in bone. In micro-CT images, the damaged region had higher intensity and could be differentiated from the healthy bone tissue, indicating that microdamage was stained with barium sulfate. The staining method was also applied to study microdamage in trabecular bone. The concentration of barium sulfate in damaged specimens was higher than in undamaged specimens.

Overall, this research provided insight into trabecular bone damage mechanics by studying microdamage development, and developing an innovative new technique to study microdamage in three dimensions.