The lower extremities are the body region at greatest risk of serious injury in frontal motor-vehicle crashes. Age, sex, and body mass index (BMI) affect the risks of clinically significant lower-extremity injuries such that women, older occupants, and occupants with higher BMI are at increased risk of these injuries in frontal crashes. Computational simulation is the most efficient way to characterize the biomechanical factors that explain the effects of age, sex, and BMI on lower-extremity injury risk. This type of simulation requires a finite element (FE) model with geometry that is parametric with these characteristics. This research developed and validated such a parametric FE whole-body model and used it to explore the effects of variations in lower-extremity geometry, material properties, body size, and body shape on lower-extremity injury risk.

The parametric whole-body FE model was based on statistical models of lower-extremity bone surface geometry and cross-sectional geometry. These models were developed by morphing and fitting template FE meshes onto bone geometries extracted from CT data. Principal component analysis was applied to the resulting nodal coordinates and linear regression on principal component scores was used to develop models that describe how geometry varies with age, stature, and BMI.

The parametric FE whole-body model was developed by combining the mesh geometries predicted by the statistical lower-extremity bone models, an existing external body surface shape model, and material properties that varied with age. Whole-body FE models associated with specific sets of characteristics were developed by positioning the lower-extremity bones inside the external surface model using surface model landmarks. A template whole-body mesh was then morphed to the external surface shape using the positioned lower-extremity bone models as fixed location landmarks. Simulations were performed with these models to investigate effects of occupant characteristics on lower-extremity injury risk. Frontal crash simulations with the whole-body models showed that age and BMI significantly affect strain values and peak forces, agreeing with the hypotheses that elderly and high BMI occupants are at increased risk of lower-extremity injury.