An investigation of biomechanical mechanisms of occupant femur injuries under compression-bending load

Abstract

Occupant femur fractures occur frequently under compression-bending load in the frontal crashes of passenger cars. In order to explore the injury mechanisms and tolerances of occupants' femur in this load condition, a finite element model of the lower extremity in the sitting posture was developed based on the anatomy of a 50th percentile male. Then the model was validated against two types of cadaver tests, including three-point dynamic bending test of the femur and the axial impact test on the knee-thigh complex. A study of femur fractures under compression-bending load has been carried out using an analytical model of the curved beam. Furthermore, six virtual tests were conducted using the validated finite element model. The results show that the location of bone fractures and the tolerance of the femur depend on both bending load and axial compression. With the increasing preload of the bending moment from 0 to 676 Nm, the femur fracture location was shift from the femoral neck to the shaft. Regarding the tests with fractures occurring in the femoral neck, the tolerance of the femur is between 285 and 296 Nm. For the other tests with fractures located in the femoral shaft, the tolerance of the femur is between 381 and 443 Nm. The results indicated that the femur fractures always occurred at the femoral neck in axial impact tests on the knee-thigh complex, but in real world car frontal impacts the femoral shaft fractures can be observed frequently.