Residual stress in bone tissue plays an important role in a mechanical strength. The aim of this study is to measure the residual stress of the bone axial direction at the cortical surface of the diaphysis in rabbit extremities. Cortical bone is a composite material composed of hydroxyapatite (HAp) crystals and collagen fibers in the nanoscale. X-ray diffraction can be used to measure the interplanar spacing of HAp crystals in the cortical bone, and then the lattice strain can be calculated by the deformation of the interplanar spacing from a reference state. We have proposed the sin
method of X-ray diffraction as the method for residual stress measurements in bone tissue. In the method, the residual stress can be estimated from the deformation of the interplanar spacings orientated to many directions in HAp crystals. In this experiment, the rabbit extremities were used: femur, tibia / fibula, humerus, and radius / ulna. The residual stresses of the bone axial direction were measured at anterior and posterior positions on the cortical surface of the middle diaphysis of each bone specimen. These specimens were kept in saline until just before the X-ray measurements. The tensile residual stresses were observed for the bone axial direction at the cortical surface of every specimen. The mean value of residual stresses at the hindlimb bones was 1.4 times higher than that at the forelimb bones. In the femur, the residual stress at the anterior position was larger than that at the posterior position, while in the tibia, the residual stress at the posterior position was larger than that at the anterior position. In the forelimb bones, the residual stresses at the anterior positions were larger than that at the posterior positions.