RELATIONSHIPS BETWEEN BONE MORPHOLOGY AND BONE ELASTIC PROPERTIES CANBE ACCURATELY QUANTIFIED USING HIGH-RESOLUTION COMPUTER RECONSTRUCTIONS

It would be advantageous if the mechanical properties of trabecular be nt: could be directly inferred from stereomorphometric parameters. For that purpose, apparent density and mean intercept length. as measures of bone mass and directionality (fabric), are commonly correlated wit h the elastic characteristics of bone samples, as determined in compre ssion tests. However, complete and accurate relationships have not yet been established in this way This may be due not only to the occurren ce of artifacts in both the stereomorphometric and the mechanical asse ssments but also to an inherent inadequacy of mean intercept length in characterizing the full mechanical significance of bone architecture or nonhomogeneities in trabecular tissue properties not accounted for in stereomorphometry. In this study, we introduce a computer modeling approach allowing these biases to be eliminated. With use of high-reso lution three-dimensional computer reconstructions of trabecular bone s pecimens for stereomorphometry and for microstructural finite element models to simulate mechanical tests, unbiased comparisons become feasi ble. The purpose was to investigate if accurate and complete relations hips can be established in this way. Four different fabric measures we re considered: mean intercept length and three volume-based ones. Comp liance matrices were calculated from fabric tensors, with use of the m athematical relationship proposed by Cowin for 29 vertebral whale-bone specimens. These were correlated with the compliance constants determ ined directly from the microstructural finite clement model simulation . The nine orthotropic elastic constants of all 29 specimens were well pre dicted from their stereomorphometric fabric and volume fraction v alues, with correlation coefficients ranging from R-adj(2) = 0.9934 to 0.9963. When individual compliance components were considered (1/E-i, 1/G(ij), or -nu(ij)/E-i). correlation coefficients ranged from R-adj( 2) -0.924 to 0.982. ALI four fabric measures performed equally well. I t is concluded that volume fraction and fabric measures correlate high ly with the apparent elastic properties of bone samples, provided that anisotropy and nonhomogeneity in the elastic properties of the trabec ular tissue itself have negligible effects on the apparent properties. Whether this is true for bone in general remains to be seen, as only a subset was analyzed here. These methods, however, can be valuable in similar assessments of other subsets.