TITLE: STUDY OF DEFORMATION AND FAILURE MECHANISMS IN THE HUMAN VERTEBRA
ABSTRACT: Vertebral fractures are the most common type of osteoporotic fractures. These fractures are well known for their high association with impaired quality of life and increased risk of death. Accurate estimates of an individual’s risk of vertebral fracture are necessary for better treatment and prevention of these fractures, but these estimates have remained elusive. This dissertation project seeks to fill gaps in knowledge that exist regarding deformation and failure mechanisms in the vertebra, as a prerequisite for developing better indicators of fracture risk.
The first part of this work focuses on the use of finite element (FE) models derived from computed tomography (CT) scans of the spine. Compared with currently used clinical methods, CT-based FE models have the advantage of integrating patient-specific geometry, imaging-based material properties, and physiological loading conditions to predict the mechanical behavior of the vertebra. However, recent findings suggest that poor estimates of material properties may be a major cause of prediction errors in these models. The first two studies in this dissertation therefore sought to determine how different constitutive models for bone tissue material properties influence the accuracy of the FE predictions of deformation and failure of the vertebra. One study examined the role of fabric, a measure of microstructural anisotropy, and the other compared two different yield criteria. In both cases, displacement fields measured experimentally in prior work were used as the ground truth in the calculation of prediction errors.
The second part of this work focuses on deformation and failure of the vertebral endplate, a thin platform of mineralized tissue at the top and bottom boundaries of the vertebra where it connects with the intervertebral disc. Clinical observations have revealed that the vertebral fractures frequently occur in the region of the vertebral endplate, but the mechanical behavior of this region is incompletely understood. The final study in this dissertation therefore seeks to quantify the macroscale and microscale mechanical properties of the vertebral endplate. Four-point bend tests are analyzed using elasto-plastic beam theory and computational modeling to compute the elastic, yield, and post-yield properties. The associations between these properties and various measurements of microstructure and composition are then determined.
The outcomes of this project are expected to help us better understand the mechanical behavior of vertebra eventually lead to improved estimation of vertebral fracture risk under the clinical setting.
COMMITTEE: ADVISOR Professor Elise Morgan, ME/MSE/BME; Professor Harold Park, ME/MSE; Professor Katherine Yanhang Zhang, ME/BME/MSE; Professor Paul Barbone, ME/MSE