Polychromatic X-ray measurements of anisotropic residual stress in bovine femoral bone

It is well known that bone has the capability to adapt to a normal mechanical environment and to reconstruct functionally its structure and geometry. This phenomenon is called adaptive bone remodeling. One of the most important mechanical factors of remodeling is stress. To induce bone remodeling, some stress should be present to stimulate the osteocyte over a relatively long period. Thus, this stress is a type of residual stress. To verify this assumption, it is necessary to measure residual stress in intact bone tissue. Bone has an extremely anisotropic structure which consists of hydroxyapatite crystals. In this work, the polychromatic X-ray diffraction method is used to measure anisotropic residual stress in compact bone. The interplanar spacing of hydroxyapatite in bone can be measured by this method. The ratio of atomic interplanar distance of a strained specimen to that of a nonstrained one is defined as lattice strain. Biaxial residual stress is calculated from the lattice strains measured in three directions. The compact bone of bovine diaphysis is used as the specimen. To observe the difference of residual stress dependent on the region, the specimen is taken from the middle part of the diaphysis that was divided into four parts: anterior, posterior, medial and lateral, for each bone in the axial and circumferential directions. As a result, it was confirmed that residual stress in the bone could be measured nondestructively by this method. Tensile residual stress was found in the axial direction of bovine femoral bone.