Correlations Between Geometric and Material Properties of Vertebral Bodies and Their Compressive Strength

Abstract

Osteoporosis is a disease characterized by reduced bone strength leading to an increased fracture risk. Current diagnostic best practice involves measuring the bone mineral density (BMD) of a patient using absorptiometric imaging tools. This measurement is compared to a known value in order to compute fracture risk. This assessment of bone quality is based solely on the BMD, which has been shown to make up only a portion of the explanation of bone strength. The extent of BMD's contribution to bone strength is also extensively debated and widely varying in the scientific literature. This thesis work encompasses a preliminary investigation into factors in addition to density that contribute to bone strength. The geometric and material properties of 21 vertebral functional unit specimens were measured using dual energy absorptiometry (DXA), pQCT (peripheral quantitative computed tomography) and HCT (helical computed tomography) techniques. The strength of the functional units was assessed through mechanical testing under compressive loading conditions. These measurements were amalgamated into multiple linear regression models to characterize vertebral strength in terms of a few key variables. The model developed for failure load had a coefficient of determination of 0.725 and indicated that the volume of the vertebral body as well as the cross-sectional area of the cortical region were significant in the explanation of failure load. A model was also developed for stress at failure which indicated that the vertebral body height and cortex concavity were important parameters. The coefficient of determination for this model was 0.871. The goal of this study was to provide a foundation on which further investigation into the explanation of bone strength could be built. Ultimately, a better understanding of the parameters that affect bone strength will provide a basis for more accurate clinical tools for the diagnosis of osteoporosis.