Development of Human Lower Limb and Pelvis FE Models for Adult and the Elderly

It has been difficult to evaluate injuries to the elderly whose body tolerance is lowered due to aging. The objective of this study was to develop human FE models for evaluating skeletal injuries to the lower limb and pelvis of both adult and elderly people. From traffic accident statistics, 35 and 75 years old (y.o.) were defined as the representative ages of adult and elderly population. An existing human FE model for an adult male pedestrian was adopted for the baseline. Femur models were developed first, because there existed most sufficient data of material properties and geometry for the femur. Age-related changes in material properties and geometries of bone were investigated by literature survey, from which average values of Young’s modulus, yield stress/strain and ultimate stress/strain, section areas and cortical bone thicknesses for 35 and 75 y.o. were determined. As no age-related material data were found for the tibia and fibula, those of the femur were scaled with scale factors derived from some existing data. Using these parameters, the baseline model was modified to represent 35 or 75 y.o. male both in material properties and geometries. The femur, tibia and fibula models were validated against quasi-static and dynamic 3-point bending tests for force-deflection responses of respective generations, which resulted in good agreement. For the pelvic bones, as no material data were found in the literature, the parameters of the femur were initially used and then modified so that the force-deflection curves of the pelvic bone models fell within the corridors of those of side impact tests in several conditions. The validated part models were integrated into a lower body skeletal model, which was finally validated against a number of experiments with age information including knee impact and sole impact.