The ability of three-dimensional structural indices to reflect mechanical aspects of trabecular bone

Bone mineral density (BR;ID) and bone microarchitecture are important deter minants for the mechanical properties of cancellous bone. Although BMD alon e is a good predictor of average mechanical properties of cancellous bone, there remains unexplained variation in mechanical properties that might be due to missing information regarding bone microarchitecture. Recent develop ments in three-dimensional (3D) structural analysis have provided possibili ties for measuring a variety of structural indices to characterize bone mic roarchitecture, The objectives of this study were to calculate structural i ndices and elastic constants of human cancellous bone from different skelet al sites and to investigate the predictive value of different 3D structural indices for the elastic properties of bone, A total of 237 cancellous bone samples taken from the iliac crest, lumbar spine, femoral head, and calcan eus were imaged with a 3D microcomputed tomography (mu CT) system. The segm ented 3D images were used to calculate BV/TV, BS/TV, Tb.Th, Tb.Sp, Tb.N, an d hill, ratio and for microstructural finite-element (mu FE) analysis to ca lculate Young's moduli, shear moduli, and Poisson's ratios. ii subgroup of "critical" specimens within each site was selected to represent specimens t hat could not be identified as osteoporotic or normal on the basis of BMD m easurement alone. For these "critical" specimens, structural indices and el astic constants were correlated by means of linear multivariate regression analysis. It was found that the elastic constants clearly correlated better when one of the 3D structural indices was included as independent variable than when BV/TV was the only independent variable. Each of the examined st ructural indices could improve the correlation: the R-2 values were maximal ly increased from 53% (BV/TV alone) to 82% (BV/TV and MIL ratio). The most effective indices, however, were not the same for the different skeletal si tes. Even better correlations were found when more than one of the 3D struc tural indices were included as independent variables: the R-2 values were m aximally increased from 53% (BV/TV alone) to 92% (BV/TV, Tb,Sp, and Rm rati o), The prediction of elastic constants for cancellous bone samples is clea rly improved when BV/TV is supplemented with 3D structural indices. These r esults suggest that the determination of mechanical properties of bone and the diagnosis of osteoporosis can be improved if, in addition to BMD, the 3 D bone microarchitecture is assessed in vivo, (C) 1999 by Elsevier Science Inc. All rights reserved.