UBC Theses and Dissertations
Quantifying the response of vertebral bodies to compressive loading using digital image correlation Gustafson, Hannah Marie
Understanding vertebral mechanics is of interest for identifying persons at risk of fracture, whether that is due to everyday loading such as in osteoporotic fracture or as a result of dynamic loading leading to a traumatic fracture. Vertebral fractures negatively impact the quality life of patients and represent a large financial burden on the healthcare system. A powerful but underutilized tool that can be used to study vertebral loading and fracture is digital image correlation (DIC). DIC is a non-contact optical method for measuring the displacement on the surface of materials, including bone. In this thesis, DIC was used in a laboratory setting to provide a more complete understanding of the response of vertebral bodies to compressive loading. The first investigation compared measurements from DIC with strain gages, a commonly accepted experimental method for measuring the bone surface response. For porcine vertebral bodies, the agreement was strong between the strain gages and DIC-measured strains indicating that DIC can be successfully used on bone. Based on those findings, experimental studies were performed using DIC to identify fracture of the anterior cortex and to quantify rate-dependency of the vertebral body response. For the fracture study, high DIC strains on the anterior cortex of vertebral bodies corresponded well with the locations of damage identified by observation of the video. For the rate-dependency study, the DIC displacement patterns were similar for the slow and fast rate tests, but the displacements from the slow rate tests had higher magnitudes, as expected for viscoelastic materials such as bone. Finally, specimen-specific finite element (FE) vertebral body models were created and DIC was used to validate the displacement and stiffness response. The FE models were predictive of the experimental stiffnesses measured using DIC on the surface of the vertebrae. This thesis demonstrates the utility of DIC for experimental vertebral body investigations and for validation of FE models. Through these studies and future work, DIC has advanced and will continue to advance the understanding of vertebral mechanics under everyday loads as well as in simulated osteoporotic and healthy bone trauma.
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