Osteoporosis is characterized not only by a reduction in bone mass but also by alteration in the architecture of trabecular bone. Changes in BMD have long been considered the most important factor in the diagnosis of osteoporosis and in predicting the risk of fractures caused by osteoporosis. However, recent studies have demonstrated that similar BMD values have been associated with different osteoporosis-induced fracture outcomes. Changes in the trabecular architecture of the osteoporotic vertebral body are well known, but quantitative analysis of trabecular structure and its correlation with BMD have not been well studied.
The BMD measured on 39 vertebral bodies from 11 human cadavers using DEXA showed a reverse correlation with anisotropy of the trabecular orientation of the vertebral body. The anisotropy was defined as the ratio of the intensity of vertical trabecular orientation to the intensity of horizontal trabecular orientation (vertical/horizontal) measured with the two-dimensional Fourier transform of the soft X-ray of the vertebral body (Fig. 13). The study demonstrated a significantly lower BMD and higher vertical trabecular orientation in the osteoporotic vertebral body. This phenomenon also was found even within a vertebral body (anterior one-third), which corresponds to the higher incidence of the vertebral fracture in the anterior part of the vertebral body (a wedge-shaped fracture).
An increasing number of studies indicate that, in addition to BMD, trabecular microstructure is an important factor in the assessment of osteoporosis. The prediction of fracture risk in osteoporotic bone based on BMD measurement alone has been reported to be insufficient. The prediction of fracture risk using BMD measurement could be improved by incorporating the changes in trabecular orientation of vertebral body.
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