Development of a Lower Limb Digital Twin Model for Analyzing Femoral Injuries in Elderly CPC Subjects

In car-pedestrian collisions (CPC), most studies have focused on injury analysis using youth models. However, the mechanical performance of bones and muscles naturally deteriorates with age. Compared with younger people, the elderly are more vulnerable to bone fracture when subjected to the same impact. In this study, a digital twin model of the elderly lower limb (DTM-ELL) and a digital twin model of the youth lower limb (DTM-YLL) for Chinese 50th-percentile males were developed based on CT images, in which 150 material properties were assigned to the bones according to their Hounsfield units. The digital twin model of the lower limb (DTM-LL) was validated through quasi-static three-point bending simulation and dynamic lateral loading simulation of the knee joint. A family-car lateral impact simulation was used to verify the consistency between the developed model and THUMS (Total HUman Model for Safety). Through collision simulations between each of three car models and the DTM-LL, it was found that the maximum average stress in the femur of the DTM-ELL is 62.64% of that of the DTM-YLL under the same CPC conditions. Surrounding soft tissues, acting as effective cushioning during CPC, reduce the maximum femoral stress by 29.56% relative to the model without surrounding soft tissues. Finally, a real CPC accident was reconstructed in finite element software using the DTM-LL developed from the CT images. The reconstruction results showed that the DTM-LL had acceptable biofidelity and can be used to study femoral injuries in elderly pedestrians involved in CPC.