The Research On Child Neck Injury In Vechile Impact

Motor vehicle crashes (MVCs) are the main factors that cause the child neck injuries. About60%to80%of all pediatric spinal injuries are in the cervical region. Compared to adults, the mortality rate among victims of pediatric spinal trauma is higher. Children have different anatomical and physiological features compared to adults, such as the laxity of ligaments, decreased angle of facet joints, immature vertebral bodies, insufficiently developed neck musculatures, and relatively large head mass. These make the pediatric neck injuries different from that of adult in MVCs. Due to the ethics and laws, very few studies focused on pediatric injury in MVCs. In order to improve the safety of children in MVCs, more studies on the child neck injuries need to be conducted urgently.This study analyzed the10-year-old (10YO) child neck injuries in MVCs using the finite element (FE) method. The methods of obtaining the child material data and modeling the child neck model were provided. The injury characteristics and mechanisms for child neck were studied by simulations. These methods could help researchers to create more accurate child FE model to study the injury characteristics and mechanisms for child neck in MVCs. Using the FE model, the protective measures could be designed and evaluated to improve the safety of children in MVCs. The detailed contents and innovative points for this study are as follow:(1) A method obtaining the material data for children was provided. Due to lack of pediatric specimens, it was difficult to obtain the child material data through experiments. The existing child cervical spine models didn’t yet provide the method to obtain the child material data. Those limited the studies on child neck injuries. This study provided the method to derive the child material data by combining the scaling method, the Pareto method, and main chart plot through two steps. Step1:get the child data by scaling method based on the adult data; Step2:determine the main material factors using the analysis method of Pareto and main chart plot. Such a two-step method considered not only the geometry difference between child and adult, but also the characteristics of the child neck material. The validity of this method was verified by comparing the simulation results with the experiment data. This method could help researchers to create more accurate child cervical spine models.(2) A method of modeling a10YO child ligamentous cervical spine FE model was presented to improve the accuracy for predicting child cervical spine injuries. The existing child cervical spine models were mostly created by scaling down the adult models and using the elastic material properties. In this study, the average dimensions of cervical vertebral body for10YO children were obtained from24pediatric subjects. A child CT dataset to get the neck geometry was selected by comparing the vertebral body sizes of the selected dataset with the average values. Based on the geometries, the cervical spine FE model was created, including the unique structures for child. To improve the accuracy of predicting the material properties, nonlinear material constitutive models were used. The parameters for the material models were determined using the child data obtained from this study. The failure of soft tissue was also considered in the model by defining the failure parameters. The model was validated at three segments (C0-C2, C4-C5, and C6-C7) as well as the whole cervical spine (C0-T1) against the experimental data. The consistency between the simulation results and experimental data proved the reliability of this modeling method. The model-predicted failure positions and failure progressions of soft tissues provided the data that corroborated child cervical spine tests.(3) An original modeling method for neck muscle was presented to improve the accuracy of neck model. The method of optimizing the muscle activation curves using response surface method (RSM) that’s based on radial basis functions (RBFs) was provided to solve the optimization problem for muscle activation signals. The application of the sensitivity analysis method to study the effects of activation muscles on head responses was presented. The existing muscle models were simplified in geometry, and did not consider the effects of muscle geometries. The existing studies did not determine the types of muscle activation curves, and the effects of activation muscles on neck responses could not obtained by tests. In this study, three neck muscle models were simulated to study the effects of muscle geometry. The comparison results between simulations and experiment data showed that the geometry remarkably affected the head responses. The new muscle model could predict the head and neck responses better. The RSM that’s based on RBF was used to obtain optimized muscle activation curves for the new muscle model. This method improved the computational efficiency to find the optimized solutions. A method to evaluate the effects of active muscles on the head and neck responses was used. The main effect activation muscles were determined by calculating the evaluation values.(4) For children who have not fully developed the structure and material, a material and geometry sensitivity study was conducted using the cervical spine segment model to obtain the main factors affecting the responses and the characteristics of injuries for child cervical spine. Children have different geometry and material properties compared to adults. However, very few researches conducted the injury characteristic study from the perspective of geometry and material. As such, a C4-C6vertebral segment model obtained from the10YO cervical spine model was used to conduct the analysis. The factors included all the materials, the shape of facet joint, and the size of vertebral body. The analysis of variance was used to calculate the contribution of each factor on the responses. Based on the analysis results, the characteristics of responses and injuries for child cervical spine were obtained. The study results could help researchers to create more accurate child cervical spine models, and also provided the needed data for improving child injury analysis or treatment.(5) The analyses of child neck responses in impacts using the10YO child neck FE model were conducted to obtain the injury mechanisms of child neck. These analyses could make up for the inadequacies of the current studies. Due to lack of child cadaver samples and models, there is still a lack of understanding of the child neck injury mechanisms in MVCs, especially in the rear impacts. Using the developed10YO child neck FE model, the head and neck responses in frontal and rear impact were predicted. The consistence between the simulation results and experimental data proved the reliability of the simulation results. The child neck injury mechanisms were obtained by analyzing the ligament strains and bone stress distributions. The leg model was used to simulate the bony fracture force and fracture mode under axial impacts. The reliability of the material constitutive model and material parameters for the bones was verified by comparing the simulation results with the experimental data. Referring to these material data, the child data for vertebra were obtained to study the child vertebra fracture in compression. The relationship between the bony fracture force and material parameters was obtained.