Bone Quality is Dependent on the Quantity and Quality of Organic-Inorganic Phases

Background 'Bone quality' is widely used in biomedical and clinical communities, to collectively describe all bone characteristics (except bone mineral density) that influence the bone's resistance to fracture. However, a quantitative relationship between bone quality at the tissue level and bone compositions has not been established. Methods We considered bone as an organic-inorganic composite material and proposed that the quality of the bone as well as its organic-inorganic phases is measured by stiffness (Young's modulus), strength (yield and peak stress) and toughness (energy to failure) at the tissue level. To establish a relationship between bone quality and organic-inorganic compositions, we fabricated 400 cylindrical specimens from bovine leg bones. We tested their mechanical properties under axial compression (N = 200) or axial tension (N = 200). The tested specimens were then fully ashed to determine their organic and inorganic mass fractions. The stiffness, strength and toughness of bone organic-inorganic phases were determined from the tested mechanical properties and phase mass fractions using nonlinear regression. Results A novel regression equation was developed to describe the relationships between bone quality and bone compositions. Conclusion With recent advances in technologies for in vivo measurement of bone inorganic and organic content, the equation may provide new insight into bone aging and diseases.