## 4 Discussions  
Pedestrian injuries in road traffic accidents are common and serious. Among them, the pelvis and lower limbs are vulnerable parts. Pelvic fractures are a common cause of morbidity and mortality [38]. The complex mechanism of pelvic fractures is a challenging forensic issue. Commonly, the identification opinions about injury mechanisms and injury manners are often the key evidence for liability distribution, insurance compensation, and even criminal convictions. However, identification mostly relies on clinical classification and expert experience, and there is a lack of systematic understanding of the mechanism of pelvic fractures exists [21]. The commonly used clinical classification systems of pelvic fracture include the Tile [18], Young-Burgess [20] and AO [19] classification methods. However, these classifications cannot cover most of the issues encountered in forensic practices. Therefore, the application of injury biomechanical methods is necessary to evaluate the mechanism of pelvic fractures and represents a more accurate, repetitive, safer and cost-effective method for forensic purposes [39]. The correlation between injury manner and biomechanical and consequences will be established using systematic simulations, which will be conducive to forensic injury identification. The pelvis FE model has been applied to various studies. [PERSON] et al. [40] found that muscles and ligaments can reduce the stress concentration in the cortical bone based on pelvic FE simulations. [PERSON] et al. [41] and [PERSON] et al. [42] found that the public symphysis significantly affects the pelvic stress distribution. [PERSON] et al. [16] established the injury risk curve of key pelvic parts based on pelvic injury simulation data that can be used for injury quantification. Additionally, some studies on the biomechanical of pelvic injury have been close to forensic practices. [PERSON] et al. [43] found that the force on the hip joint directly affects the distribution of pelvic stress, and gait will significantly affect the pelvic stress concentration. These studies are focused on modeling and related validation, mainly applied to automotive safety and clinical treatment. The loading conditions are relatively simple and unsystematic and cannot be directly applied to forensic identification. Our study is based on the THUMS model, which has been widely used and fully validated, to carry out systematic injury conditions to investigate the effects of different impact and run-over loading on pelvic fractures. We employed a real postmortem human pelvis side impact experiment result to validate the fracture performance of the THUMS model, indicating that the model can predict the fracture response and is suitable for this study. A total of 54 simulations consist of two injury manners (impact and run-over), seven loading directions (\(0^{\circ},30^{\circ}\), \(60^{\circ}\), \(90^{\circ}\), \(270^{\circ}\), \(300^{\circ}\), \(330^{\circ}\)), and six loading velocities (10 km/h, 20 km/h, 30 km/h, 40 km/h, 50 km/h, 60 km/h) were conducted (Table 2). The quality of all simulation results has been checked and all of them comply with the current industry standard requirements, which indicates that the results are credible under the current state of the art [30]. Because the prediction ability of the strain criteria has been verified experimentally [32,33], we used the effective strain contours to compare the fracture responses among all the loading conditions. The results show that the loading directions have a significant effect on the fracture responses; for example, the \(90^{\circ}\) and \(270^{\circ}\) impacts resulting in fractures were obviously slight, likely attributed to the cushioning effect of amounts of soft tissue in the buttocks and easy flexion and movement of the pelvis during front impact. Additionally, we found fractures on the opposite side of the impact (e.g., \(30^{\circ}\), \(60^{\circ}\) and \(300^{\circ}\)), which should be related to the overall pelvic ring deformation.