The Influence of Hindlimb Unloading on the Bone Tissue’s Structure

The results of numerous studies indicate interactions between antiortostatic support and bone’s tissue. It is known that mechanical, genetic, endocrine, and age-related factors can influence the bones at the same time. Nevertheless, the physiological and pathological mechanisms of interconnection between unloading hindlimb and bones are largely unclear. The purpose of this study is to evaluate the correlation between unloading hindlimb and changes in bone’s tissue. After unloading of the hindlimb during 14 days, femoral bones were collected in order to evaluate the weight, density, and geometrical bone parameters. Additionally, a test with a three-point bending and computed tomography scanning was carried out. Using computed tomography data, fabric tensor was built. From the assumption that the bone tissue is orthotropic (exists a maximum of three mutually orthogonal axes with different material properties), we performed this analysis. Orthotropic properties of the bone tissue were analyzed in assumption that the principal direction of the fabric tensor is coaxial with the axes of orthotropy of the material. It was found that the axes of orthotropy of the bone tissue in the cross section are mostly directed in tangent direction, and after hindlimb unloading, axes of orthotropy rotate 90° (became directed in radial direction). Anisotropy ratio in the cross section changes significantly. Meanwhile, Young’s modulus and ultimate strength decrease. It shows that unloading of the hindlimb aggravates quality of the bone tissue.