Estimation of various mechanical characteristics of human bones using dual energy X-ray absorptiometry: methodology and precision.

The mechanical competence of bone is determined by its macroscopic geometric characteristics [size, shape, apparent density (BMAD), cortical thickness (CWT), cross-sectional area, trabecular architecture], intrinsic material properties (stiffness, strength), and loading conditions (mode, direction, rate) at a given skeletal site. The main objective of this study was to introduce precise methods for further analysis of dual energy X-ray absorptiometric (DXA) data and for estimating macroscopic mechanical characteristics of bone at several skeletal sites representing both the axial and appendicular skeleton. This study showed that using computational BMAD, CWT and dimensional parameters, different site-specific mechanical characteristics (stiffness and strength indices) of a typical long bone (a bone consisting of both the cortical shaft and trabecular metaphyses and epiphyses at both ends) can be approximated with a low precision error (generally < 2%). The efficacy of a study applying DXA may be further enhanced by applying relevant site-specific parameters (different parameters for bone ends and shafts) for evaluation, the parameters based on the anatomic ROIs. Evidently high-quality operator performance is a prerequisite for effective accomplishment of longitudinal studies, especially when small changes in bone characteristics are expected. It should be kept in mind that to some extent the inherent two-dimensional nature of the DXA measurement compromizes the potential efficacy of the presented methods since some simple assumptions had to be made regarding the geometry and structure of bone. Nevertheless, in this study the observed values were consistent with those found by other investigators. Further experimental studies are needed for direct site-specific validation of the proposed analytic methods.