Injury Pattern and Response of Human Thigh under Lateral Loading Simulating Car-Pedestrian Impact 2004-01-1603

The main objective of the present study is to determine experimentally the injury patterns and response of the human thigh in lateral impacts simulating more closely the real impact conditions in car-pedestrian accidents. We conducted in-vitro experiments on thirteen thighs of eight completely intact Post Mortem Human Subjects (PMHSs). The thigh was hit by a ram at a speed of 35 km/h at the mid-shaft of the femur in each completely intact PMHS. Since the effect of cumulative injuries should be avoided, each thigh was impacted only once. Three impact energies were used; 450J, 600J and 700J. The PMHS motion was not constrained so as to simulate the walking posture of a pedestrian. We analyzed the peak values of the impact force of the ram and the femur acceleration. Injury was assessed by dissecting the lower extremities.

The main injury sustained at the impact energy of 600J and 700J was either a femur diaphysis wedge fracture or a femur complete oblique fracture accompanied by an incomplete fracture line that nearly produced a wedge. In test results obtained by means of one PMHS, a knee ligament injury was observed at the impact energy of 450J (left thigh), while a femur wedge fracture was observed at 600J (right thigh). Therefore, the type of injury was affected by the impact energy level. Based on the present data regarding the normalized impact force and femur fracture, the risk curve for a femur fracture was determined. This risk curve indicated that the normalized impact forces of 8.8 kN and 9.5 kN corresponded to a 0.2 and 0.5 probability of femur fracture, respectively. The mean maximum normalized femur acceleration in femur fracture cases (207 G (SD 58)) was lower than that in no injury (intact) cases (266 G (SD 63)). This suggested that femur acceleration was not a good indicator of femur fracture in this study.