The human femur is subjected to an impulsive load at its distal end during daily life. Femoral bone fracture caused by impact loading is common in elderly women. It is important to clarify the dynamic response of the femur and to evaluate the change in its stress state during impact loading. A 3-dimensional model of the femur was prepared in the present study, and the impulsive stress waves propagating from the distal end of the femur were analyzed by the dynamic finite element method. This model showed that the von Mises equivalent stress is large on the anterior and posterior sides of the mid-diaphysis when the impact direction is different from that of the bone axis. As for the femoral neck, the absolute value of minimum principal stress initially increases on the medial side;slightly later the maximum principal stress increases on the lateral side. In this case, the absolute value of the maximum principal stress was found to be larger than that of the minimum principal stress, and the absolute value of the principal stress decreased as the impact angle increased. Further, the femoral neck and the trochanter were shown to have a higher risk of bone fracture when the impact direction is coincident with the bone axis
