Measuring the structural strength of bones with dual-energy X-ray absorptiometry: principles, technical limitations, and future possibilities

Excerpt

The fundamental problem in osteoporosis is that it reduces the mechanical strength of bones so that in certain skeletal locations fractures occur with minimal trauma. The ideal clinical assessment would measure bone strength at likely fracture sites and determine whether weakening has occurred; moreover, it would do so with sufficient precision to detect significant changes in strength. This is currently not possible with density-based measurements for fundamental reasons. Unquestionably, bone density has firm statistical links with osteoporosis and osteoporotic fracture and can be conveniently measured by a variety of means with reasonable accuracy and precision. Unfortunately, density does not unambiguously measure any known mechanical property. Regardless of the accuracy of a density measurement, it cannot in isolation provide insight into the effects of osteoporosis on bone strength. The question then remains, can bone strength be directly and reliably measured in vivo, especially at those sites where osteoporotic fractures occur? The purpose of this essay is to define the material and structural components of strength and to examine the potential of one method for measuring structural strength using DXA scan images. The limitations of this method will be described, as will approaches for mitigating those limitations. …