Transverse isotropic elastic properties of vertebral trabecular bone matrix measured using microindentation under dry conditions (effects of age, gender, and vertebral level)

The mechanical properties of bone extracellular matrix have become of increasing interest for the understanding of vertebral fracture risk. Depth-sensing indentation techniques allow the measurement of directional elastic properties of trabecular bone ex vivo with a high spatial resolution. Transverse isotropic elastic properties of vertebral trabecular bone obtained from two orthogonal directions were investigated using microindentation under dry conditions focusing on the influence of microanatomical location, age, gender, vertebral level, and anatomic direction on these properties. Biopsies were obtained from 104 human vertebrae (T1L3) with a median age of 65 (2194) years. Significantly, higher indentation moduli were found for indentations on axial than on transverse cross-sections of trabeculae (p <0.01). Indentation moduli in the core were 1.05 to 1.12 times higher than in the periphery (p <0.01). No difference in stiffness could be detected between males and females (p > 0.05) and different ages (p > 0.5). Vertebral level showed a weak correlation (p = 0.073, r² ≈ 0.17). These results provide insights in the transverse isotropic properties of trabecular bone matrix related to age, gender, microanatomical location, and anatomic direction for a broad spectrum of human vertebrae.