Master's Theses

Date of Award

2011

Document Type

Thesis

Department

Biomedical Engineering

Keywords

Bone, Biomedics, Fragility

Abstract

"Bone strength deteriorates with age; which increases the susceptibility to fracture. Current clinical techniques for the estimation of bone strength are largely Bone Mineral Density (BMD) based. However, toughness, which is the ability to resist crack growth, plays a critical role in bones‟ fracture resistance. Traditionally, toughness measurements involve large samples, obviating their use clinically. Recent data suggest that a reference point indentation approach provides a novel, localized measure of toughness from whole bones. In the current research, we evaluated the sensitivity of this method to discriminate small known differences in fracture toughness that exist between inbred mouse strains with genetically based differences in mineralization. To achieve this we measured a new parameter called Indentation Distance Increase (IDI) which has been shown to be related to fracture toughness. We also analyzed associated microdamage patterns and the surrounding tissue microarchitecture. In addition, Tissue Mineral Density (TMD) was measured and analyzed. IDI was highest in AJ mice followed by C3H and B6 and a similar pattern was found for TMD. These data precisely parallel previously reported phenotypes for bone brittleness. Crack formation occurred under the indenter tip, suggesting that the tip acts as an “opening-wedge”. These cracks initiated in the transverse direction and were then diverted into the longitudinal direction. Other toughening mechanisms were also observed: un-cracked ligament bridging was present in C3H bones, while B6 femurs showed extensive delamination, consistent with internal slippage in the mineralized collagen fibrils. These data suggest that the reference point indentation is a suitable and sufficiently sensitive method for detecting differences in brittleness as a result of small differences in mineralization. This may have important clinical implications in the assessment of fracture risk."

 
 

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