BIOMECHANICS OF DISTAL RADIUS BONE MINERAL

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Post-menopausal osteoporosis is a national health problem of nearly crisis proportions with approximately 1.3 million fractures and estimated annual costs of close to $4 billion. While there is growing evidence that certain therapeutic measures can help retard bone loss and thus reduce fracture incidence, some treatment modalities are themselves associated with significant risks and patient costs. It becomes increasingly important, therefore, to identify those patients at risk of fracture so that appropriate therapy can be instituted. The universally accepted standard for osteoporosis screening remains single photon absorptiometric scanning to determine bone mineral content (BMC) of the distal radius. However, despite its widespread clinical use, BMC measurements reflect the combined influences of changes in bone density and cross-sectional geometry. We have shown previously that commonly applied normalization procedures (dividing by bone width) does not effectively eliminate this critical and unexplained source of variance. Since biomechanical performance varies as power law functions of the bone geometry, this may well explain the relatively poor predictive capability of photon absorptiometry of the radius in assessing fracture risk at other skeletal sites. The intent of this Pilot Project is to extend available photon absorptiometric scanning technology to allow a separation of geometric and densitometric effects. For 10 pairs of fresh-frozen cadaveric forearms from human females, we will: 1) determine BMC and BMC/W at standard clinical and two additional radial sites; 2) develop and implement new absorptiometric procedures and data reduction algorithms for the separation of cross-sectional geometric and densitometric variables; 3) physically section one radius of each pair at the scanned sites and determine cortical and trabecular areal fractions, porosity-weighted principal areal moments of inertia, and the apparent densities and mechanical properties of cortical and trabecular bone; 4) conduct in vitro failure tests of he contralateral forearm under multi-axial loading simulating a Colle's fracture; and 5) compare the discriminatory and predictive capabilities of available and experimental absorptiometric techniques against; a) direct measures of cross sectional geometry; b) bone density and material properties; and c) in-vitro fracture load. The hypothesis to be tested is that the extraction of geometric information will significantly improve the biomechanical predictive capabilities of this technique and thus serve as the basis for new and more accurate screening procedures for diagnosis and treatment evaluation in osteoporosis.