Establishment Of Finite Element Model Of Skull Based On CT Data And Study On The Stress Analysis Of Falling Injury And Striking Injury

Objective: The brain is the most important vital center of human body,and it is the organ with the highest fatality rate and disability rate.In forensic injury cases,head is often the main target.The identification of falling injury and striking injury of the skull has also been the focus in the study of forensic injury cases.This study reconstructs a three-dimensional(3D)finite element model of skull based on the CT data of normal human head.Then,to analyses mechanics of falling injury and striking injury of occipital bone using this validated model.To provide theoretical reference for identifying falling injury and striking injury of skull by using digital technology.Methods:1 A healthy female adult was selected as the simulation object and the data of skull were collected by spiral CT.2 A 3D geometrical model of skull was created using Mimics 15.0software and Geomagic Studio 12.0 software.3 A finite element model of skull was created using 3-matic 7.0 module of Mimics 15.0 software and Explict Dynamic(LS-DYNA Export)module of ANSYS Workbench 14.0 software,.4 Compare with Yoganandan’s cadaver experiment to verify the validity of this finite element model.5 Analyse the stress propagation path,the region of stress distribution,force-time curve,pressure of impact position and contrecoup position caused by falling injury and striking injury of occipital bone using ANSYS Workbench 14.0 software and LS-DYNA 971 software at the speed of 5.1 m/s,6 m/s and 10 m/s,respectively.Results:1 A 3D geometric model of the skull except mandible and hyoid was successfully set up.2 A finite element model of the skull was generated,including 1 piece of the occipital cortical bone,2 pieces of the occipital cancellous bone,1 piece of the rest skull cortical bone and 10 pieces of the rest skull cancellous bone in3-matic module of Mimics 15.0 and ANSYS Workbench 14.0 software.The total number of nodes was 238009,the total number of units was 942663.3 The finite element model of the skull was validated according to Yoganandan’s cadaver experiment.The peak contact force of this study was13323 N,which was about 5% less than that of cadaver experiment(14034N).When the contact force reached the peak value,the curve showed a downward trend,which indicated that the plastic yield of the skull had occurred.the contact force-displacement curve and that of literature experiment maintained the similarity basically,which verified the validity of this finite element model and could study on biomechanical analysis of the skull further.4 Falling injury of occipital bone of skull at different speeds were simulated combined with ANSYS Workbench 14.0 and LS-DYNA 971 software and exported the equivalent stress(Von Mises Stress)distribution nephogram.The direction of stress propagation was occipital bone-skull base–forehead mainly,The stress concentrated on the centre of occipital bone mainly,sutures around occipital bone,internal occipital protuberance,foramen magnum,occipital basis,jugular foramen,sulci sigmoideus,internal acoustic port,foramina lacerum,the tip of the petrous bone,foramen ovale,pituitary fossae,frontal bone’s orbital plate,pterion,zygomatic arch,sphenomaxillary fissure and maxilla at a speed of 5.1m/s.In addition to above positions,optic canal and lesser sphenoid wing increased at a speed of 6m/s.In addition to above positions,ethmoidal plate and glabellum increased at a speed of 10m/s.At the same time,comparing contact force-time curve of collision position at different speeds showed that the higher the impact velocity,the greater the contact force,the earlier the peak contact force reached with falling height increasing.The pressure of occiput as the impact position is positive,while thepressure of forehead as the contrecoup position is plus or minus alternately.5 Striking injury of occipital bone of skull with a hammer at different speeds were simulated combined with ANSYS Workbench 14.0 and LS-DYNA 971 software and exported the equivalent stress(Von Mises Stress)distribution nephogram.The direction of stress propagation was also occipital bone-skull base –forehead mainly,The stress concentrated on the centre of occipital bone mainly,sutures around occipital bone,internal occipital protuberance,foramen magnum,occipital basis,jugular foramen,sulci sigmoideus,internal acoustic port,the tip of the petrous bone,foramina lacerum,foramen ovale,pituitary fossae,frontal bone’s orbital plate,pterion,zygomatic arch,sphenomaxillary fissure and maxilla at a speed of 5.1 m/s.In addition to above positions,optic canal increased at a speed of 6 m/s.In addition to above positions,ethmoidal plate and glabellum increased at a speed of 10 m/s.But the range of stress concentration was smaller than that caused by falls at the same speed.Comparing contact force-time curve of collision position at different speeds showed that the higher the impact velocity,the greater the contact force,the earlier the peak contact force reached.The pressure of occiput as the impact position is positive,while the pressure of forehead as the contrecoup position is plus or minus alternately.6 At the same speed,the stress nephogram showed that stress concentration area of falling injury was wider than that of striking injury;the contact force-time curve showed that peak contact force of falling injury was bigger than that of striking injury;pressure of occiput as the impact position showed that pressure of falling injury and striking injury was almost the same;pressure of forehead as the contrecoup position showed that the range of plus or minus of falling injury was greater than that of striking injury.Conclusions:1 Based on the CT data of skull of normal human,a three-dimensional geometric model and finite element model of human skull with similar anatomical structure are reconstructed using the corresponding software.2 By comparing the curve with the classical head injury experiment,the validity of the model is verified.3 Falling injury and striking injury of occipital bone of skull are simulatesd successfully.Compares biomechanical properties of two kinds of damage.The results show that the direction of stress propagation is occiput-skull base-forehead mainly when impacting the center of occipital bone.The stress concentration region of skull is consistent with the clinical site of the skull base fracture.Under the same working condition,the greater the speed,the more prone to skull injury.The reason of forehead fracture(contrecoup position)may be fatigue fracture caused by the alternation of positive and negative pressure.4 At the same speed,the damage region caused by falling injury is more extensive,more serious and more likely to have a contrecoup fracture than striking injury.