The assessment of vertebral bone macroarchitecture with X-ray computed tomography

On a macroscopic scale, the structural characteristics of whole bone are likely dependent on the distribution of typically applied loads to the bone surface, the full bone shape, the thickness of the cortex at the various surface positions, and the distribution of cancellous bone material. X-ray computed tomography is presently the best available method for assessing the macroarchitecture of bone in-vivo. Fine detail, three-dimensional CT methods are available to measure regional bone mineral density (rBMD) in contiguously spaced small volumes and have been applied to the assessment of macroarchitecture in vertebrae. The more detailed rBMD methods produce radiation exposures to the subject similar to lumbar radiography and substantially higher than traditional QCT. The cancellous bone within lumbar vertebral bodies has been found in cross-sectional studies to have increased density in the inferior, posterior and lateral regions. Notably, regions with higher density at age 40 have a larger decline with age. The vertebral body cortex declines with age at a slower rate than observed for cancellous bone; however, the decline with age of cortical bone appears to vary substantially amongst subjects. The amount of cortical bone in the anterior portion of the body is less than in the lateral portion, which may explain previous discrepancies in assessing the fraction of vertebral body bone in the cortex.