Simulation study on mechanisms of hip fractures in backward falls

Abstract

Past researches that evaluated hip fracture risk had focused on sideways falls, while backward falls were also reported to cause as many hip fractures as the sideways falls do. To understand the mechanism of hip fracture during a backward fall, we conducted fall simulations using a "Multi-body and Finite-element Coupled Human Model". This model was effective and efficient in simulating both the kinematic behavior of the whole body and the stress distribution around the femoral neck simultaneously and in evaluating hip fracture risk resulting from the fall. In the simulations, the lateral area of the greater trochanter contacted the floor in the sideways fall, and the proximal top of the greater trochanter contacted the floor in the backward fall with the upper body tilted laterally. In the backward fall, the impact velocity and the contact force with the floor were low. However, as the geometrical relationship among the femur, hip joint, and pelvis made the contact force work more efficiently, the shearing force and the torsional moment in the femoral neck were large and the maximum values of each stress were the same or higher as compared to that of the sideways fall. Besides, the pubic rami are likely to break and thereby prevent a femoral neck fracture in the sideways fall, but not while in the backward fall. This result shows that the risk of a hip fracture in the backward fall is the same or even higher than that in the sideways fall. © 2013 by JSME.