Load transfer analysis of the distal radius from in-vivo high-resolution CT-imaging

Prevention of osteoporotic bone fractures requires accurate diagnostic meth ods to detect the increase in bone fragility at an early stage of osteoporo sis. However, today's bone fracture risk prediction, primarily based on bon e density measurement, is not sufficiently precise. There is increasing evi dence that, in addition to bone density, also the bone microarchitecture an d its mechanical loading conditions are important factors determining the f racture risk. Recently, it has been shown that new high-resolution imaging techniques in combination with new computer modeling techniques based on th e finite-element (FE) method can account for these additional factors. Thes e techniques might provide information that is more relevant for the predic tion of bone fracture risk. So far, however, these new imaged-based FE tech niques have not been feasible in-vivo. The objectives of this study were to quantify the load transfer through the trabecular network in a distal radi us using a computer model based on in-vivo high-resolution images and to de termine if common regions of fractures can be explained as a result of high tissue loading in these regions. The left distal radius and the two adjace nt carpal bones of a healthy volunteer were imaged using a high-resolution three-dimensional CT system providing an isotropic resolution of 165 mu m. The bone representation was converted into a FE-model that was used to calc ulate stresses and strains in the trabecular network. The two carpal bones were loaded using different load ratios (for each load case 1000 N in total ) representing impact forces on the hand either in near-neutral position or ulnar/radial deviation. The load transfer through the trabecular network o f the radius was characterized by the tissue strain energy density (SED) di stribution for all load cases. It was found that the distribution of the ti ssue loading depends on the ratio of the forces acting on the carpal bones. For all load cases the higher SED values (on average: 0.02 +/- 0.08 (S.D.) N mm(-2)) are found in a 10 mm region adjacent to the articular surface wh ich corresponds well with the region where Colles- or Chauffeur-fractures o ccur. We expect that, eventually, this new approach can lead to a better pr ediction of the fracture risk than methods based on bone density alone sinc e it accounts for the bone microstructure as well as its loading conditions . (C) 1999 Elsevier Science Ltd. All rights reserved.