An Investigation on the Importance of Material Anisotropy in Finite-Element Modeling of the Human Femur

Detailed finite element modeling of the human body offers a potential major enhancement to the prediction of injury risk during vehicle impacts. Currently, vehicle crash safety countermeasure development is based on a combination of testing with established anthropomorphic test devices (i.e., ATD or dummy) and a mixture of multi­ body (dummy) and finite element (vehicle) modeling. If a relatively simple finite element model can be developed to capture additional information beyond the capabilities of the multi-body systems, it would allow improved countermeasure development through more detailed prediction of performance. A simpler finite element model of human bones could be developed if it were shown that less complex finite element material modeling provides sufficient prediction of long bone macro-level strength. This study investigates the importance of including material anisotropy in the finite element model of a human femur. Four composite femur models were developed: linear orthotropic, linear transversely isotropic, linear isotropic, and non-linear isotropic. Each model was used to simulate anterior-posterior (AP) bending and external­ internal rotation. Comparison of the results with physical tests indicates that the global elastic force-deflection response of the whole femur in AP bending is sufficiently described by isotropic material models of the two constituent tissues. The more complex (more detailed anisotropic) material models do not enhance the results of this simulation. However, the global response of the femur in external-internal rotation does indicate that increased material model complexity (or higher degree of detail in material anisotropy) can provide improved prediction capability.