Non-invasive assessment of trabecular bone structural anisotropy: relevance to mechanical anisotropy.

Although there are now many theories describing empirical relationships between strength properties of bone and various explanatory variables, the need for improved non-invasive diagnostic techniques to assess bone fragility is of core importance in clinical problems such as osteoporosis. The aim of this thesis was to develop non-invasive radiological methods to assess trabecular bone architecture. Measures of structural anisotropy and bone structure from X-ray or radiological projections have been developed. The first measure, the projected mean intercept length (PMIL), allows extraction of the total bone surface (BS/TV) and the mean intercept length (MIL) from projections of trabecular structure. The second measure, the line projection deviation (LPD), is a technique that quantifies the preferential alignment of trabecular bone from projections of the trabecular structure. Hence, in combination, the PMIL and LPD allow non-invasive extraction of BS/TV and more detailed preferential alignment from projections of the trabecular structure. In this thesis the PMIL and LPD are introduced and their properties explored. The PMIL and LPD are used to examine the anisotropy and architectural properties of a number of human vertebral body trabecular bone samples. When used in combination with clinical densitometry, these measures improve explanation of the variance in strength, elastic modulus and toughness of vertebral body trabecular bone samples by up to 40% when compared to densitometric values alone. While µCT can provide the information needed to access trabecular architecture, it cannot be used in clinical settings since its high radiation dose makes it only applicable to small objects ex-vivo. At present, clinically available CT does not provide sufficient resolution to resolve trabecular structures. Thus, the methods described in this thesis will allow estimates of structural parameters from plain X-rays, providing for the first time, the possibility of clinical use of such estimates.Thesis (Ph.D.) -- School of Medical Sciences, 200