Spatial distribution of tissue mineralization and anisotropic tissue elastic constants in human femoral cortical bone

Abstract

In this study the spatial distribution of anisotropic elastic properties and tissue mineralization within a human femoral cortical bone shaft (female: 72 years) were investigated. Cylindrically shaped punch biopsy samples (diameter: 4.4 mm) were analyzed using high resolution ultrasonic cylindrical scanning microscopy (SAM, N = 56) at 50 MHz and synchrotron radiation μCT (SR-μCT, voxel size: 10 μm, N = 27). For all samples the average tissue elastic coefficients and the average tissue mineralization were derived from the SAM and the SR-μCT measurements, respectively. The impact of tissue mineralization on the five independent elastic coefficients was analyzed with respect to the anatomical location of the femoral shaft. The average values (mean ± std) of the elastic coefficients were: c33: 31.0 ± 3.0 GPa: c11: 22.0 ± 1.8 GPa; c12: 9.5 ± 1.2 GPa, c13: 10.0 ± 1.3 GPa, c44: 6.6 ± 3.0 GPa. The average tissue degree of mineralization in the cylinders was 1.10 ± 0.02 g/cm3. Weak, but significant correlations with DMB were found for c33 (R2 = 0.11, p < 10-4) and c44 (R2 = 0.008, p < 0.031). The coefficients of correlation R2 between the individual elastic coefficients were between 0.04 and 0.99. Twofactor ANOVA revealed that the axial and radial anatomical locations had significant influences on DMB and the elastic constants. However, these variations were not consistent for DMB and the elastic coefficients. These findings confirm that tissue mineralization is only a minor predictor for tissue elasticity in cortical bone.