Characterization of knee-thigh-hip response in frontal impacts using biomechanical testing and computational simulations.

Development and validation of crash test dummies and computational models that are capable of predicting the risk of injury to all parts of the knee-thigh-hip (KTH) complex in frontal impact requires knowledge of the force transmitted from the knee to the hip under knee impact loading. To provide this information, the knee impact responses of whole and segmented cadavers were measured over a wide range of knee loading conditions. These data were used to develop and help validate a computational model, which was used to estimate force transmitted to the cadaver hip. Approximately 250 tests were conducted using five unembalmed midsize male cadavers. In these tests, the knees were symmetrically impacted with a 255-kg padded impactor using three combinations of knee-impactor padding and velocity that spanned the range of knee loading conditions produced in FMVSS 208 and NCAP tests. Each subject was tested in four conditions. Following test of whole seated cadavers, the subjects were impacted after the connection between the thigh flesh and pelvis was cut, after the thigh flesh was removed, and after the torso was removed. Applied force and femur and pelvis acceleration data from these tests and results of other studies were used with data on static body segment masses to develop and validate a one-dimensional lumped-parameter model of the body. Simulation of the whole body cadaver tests performed with this model predict that approximately 54% of the peak force applied to the knee was transmitted to the hip for all three impact velocities. Additional simulations with the model in which knee impact conditions were varied over a wider range of loading conditions indicate that the percentage drop in force between the knee and the hip is relatively constant over the range of knee impact conditions that are of interest for injury assessment. Simulation results also indicate that high-rate, short-duration knee loading by a rigid surface is more likely to produce knee/distal femur fractures and less likely to produce hip fractures due to laxity in the hip that delays recruitment of pelvis mass and the development of fracture-level forces at the hip until after the fracture tolerance of the knee/femur has been exceeded.