Residual Stress and Structural Anisotropy of Cortical Bone

Abstract

The concept of residual stress and strain does not have long history for biological tissues. In the case of cortical bone, during remodeling process the old tissue is replaced by the new tissue with construction of osteons. Since the new tissue is generated under in vivo loadings as a non-deformed state, an indeterminate structure may be generated as a result of difference between the deformations of the old and new phases. Further, the mechanical properties (e.g. elastic modulus) are also different in these phases. Because of such non-uniform structures in cortical bone, residual stress/strain will remain in the replaced region even without external loading being applied. Tadano and co-workers initiated efforts to estimate residual stress/strain in cortical bone. In a very few applications with bone, the authors have successfully applied X-ray diffraction to quantify residual stresses at the bone surface. In this work, site-specific residual strain characteristics in relation with the mineral crystal orientation were studied and the sin² ψ method was applied to measure residual stresses in bovine and rabbit extremities. The relationship between residual stress and osteon population density on the respective sites has also been obtained. Thus the knowledge about residual stress/strain in cortical bone, related with mineral crystal distribution and osteon population density, might play an important role in the biomechanical aspects of bone healing and remodeling.