The density distribution and internal structure of trabecular bone are modulated by local mechanical environment.In this study,an orthotropic adaptation algorithm was applied to the 3D femur model to simulate the variations of stiffness and orientation ot trabecular bone under multi-loading conditions.This algorithm includes the determination of orthotropic axes and the stiffness modification of trabecular bone.Three methods were used to determine the orthotropic axes,i.e.the maximal cycle method,the stress maximum method,and the composite method.We found that the composite method was better than the other two.Firstly,the characteristics of density distribution obtained by using the composite method agreed better with those in real proximal femur.Secondly.the material orientation aligned with the known trabeculaer pattern.Finally,the ratios of the longitudinal modulus to the transverse modulus were also shown to be realistic in three local regions of the proximal femur.