| BackgroundBlunt traumatic brain injury is very common in forensic practice, especially in the murder case and accident death first. It have been reported a lot about the mechanism of blunt traumatic brain damage of studies. The observation and detection ways also have been from macro level such as by the naked eye to by light microscope, immunohistochemical and molecular biology, and so on as the microcosmic level. But it have been not so much research in craniocerebral injury biomechanics response, such as violent factors of craniocerebral injury force parts, power transmission, the local stress and strain, the relationship between deformation of craniocerebral injury and the change of intracranial pressure, etc. It is difficult to reproduce the damage process objectively and accurately getting through the single traditional identification and research methods. It is also difficult to explain the craniocerebral injury biomechanics response and threshold quantization clear. As a result it is not so easy to meet the requirement that the scientific evidence should be objective and quantitative. Especially sometimes it is difficult to judge that the blunt traumatic brain injury caused by fall or by blow, which make it difficult sometimes for the case judgment and brought inconvenience criterions for the conviction.Nowadays, people pay more and more attention in forensic biomechanics research and application as the rapid development of biomechanics technology and combine with medical discipline More closely. It can be explain the mechanism of craniocerebral injury clear through the biomechanics analysis of craniocerebral injury, and could be get help to determine the way of craniocerebral trauma injuries.So far, human skulls, animals, artificial physical models, head of two-dimensional or three-dimensional finite element models and so on experimental methods have been used by the domestic and foreign experts and scholars to study the mechanism of craniocerebral injury, and a lot of achievements have been achieved. Different experimental models in the study of craniocerebral injury biomechanics mechanism has their own advantages, but at the same time there is also some shortcomings in a single experiment of these model experiments. For example, it could quantify injury parameters and the damage degree relationship by observing animal behavior, pathological physiological changes, and other indicators before and after the craniocerebral injury. However, there are significant difference of anatomy structure between animals and human. It is inappropriate for the experiment results of animals to be used in forensic identification of craniocerebral injury. The strain, intracranial pressure and skull fracture threshold obtained from human skull specimen experiments could be used for revealing the mechanism of traumatic brain injury and developing head protection appliance directly. However, the cadaveric heads specimen is very precious and is not easy to acquire.It can recreate the damage process and show the macro kinematics characteristics of head trauma by head finite element model(FEM) experiment under the action of external force. However, there are also differences between the finite element model experiment and real situation, including the skull in the process of damage response can reflect pathological physiology change of organisms but the FEM can’t.From what has been discussed above, there are some advantages and also some disadvantages for different single experimental model. To study craniocerebral injury mechanism comprehensively, it is best to combine some experimental methods together for comprehensive study. Therefore, this study intended to use human skull specimen, the finite element model of the head, rabbit and so on to explore the mechanisms of head acceleration and deceleration injury analysis their differences. Thus, we study the mechanism differences of head trauma caused by fall and blow, mainly from the perspective of biomechanics, to provide some references for the identification of head trauma caused by fall and blow in forensic practice.Chapter 1 Biomechanical Mechanism Research in Acceleration and Deceleration head trauma by Cadaveric HeadsObjectiveCarried on the impact and fall experiments with fresh cadaver head specimens, to study the differences of biomechanical mechanism in acceleration and deceleration head trauma.Method1、Experiment preparationTwo fresh frozen corpse skull specimens were used. Scalp in the frontal, occipital, right temporal region of the head was cut and the periosteum in the same region was shaved to make the surface of the skull exposure. Grease and other impurities were removed at the surface of the skull. Stress sensor was installed at the tail of impact hammer. Intracranial pressure sensors and strain gages were installed at the surface of the skull in the frontal, occipital, right temporal region.2、Impact experimentHead specimen was hung before the biological impact machine platform above, occipital face the impact hammer head. The impact head flat was a hard cylinder and which diameter was 6 cm. BIM-Ⅱ level biological impact machine was used. The impact speed was 0.68,0.70,0.73,0.76,0.85,0.9 MPa respectively. The process was recorded by the high-speed video camera. The head was scaned before experiment and after each impact experiment by CT. Then the slices were reconstructed in 3D model by mimics, from which the skull fracture could be observed. The skull fracture was observed and comparied with 3D reconstruction result after the impact experiments. Results of the parameters such as stress, strain, intracranial pressure data were collected by the collection system automatically and stored.3、Fall experimentA square steel plate was fixed as the contact plane with head in the fall experiment. The contact surface of the head was occipital region. The head specimen was fall from seven height of 0.6m、0.9m、1.0m、1.3m、1.6m、1.8m、2.0m respectively. The head specimen was scaned before experiment and after each fall experiment by CT. Then the slices were reconstructed in 3D model by mimics, from which the skull fracture could be observed. The skull fracture was observed and comparied with 3D reconstruction result after the fall experiments. Results of the parameters such as stress, strain, intracranial pressure data were collected by the collection system automatically and stored.Result1 Impact experiment1.1 Peak impact forceThe peak impact force increased ladder-like as hydraulic pressure increased. The biggest peak force appeared at 0.76 MPa, and then reduced (P<0.05).1.2 Peak accelerationThe peak acceleration increased with hydraulic pressure (P<0.01).1.3 Peak intracranial pressurePeak intracranial pressure in frontal increased with hydraulic pressure. Peak intracranial pressure in occipital and temporal reached top in group 0.73 MPa then decreased (P<0.05). Comparison of the occipital, temporal, frontal three parts, occipital peak intracranial pressure was maximum (0.68MPa group temporal was most max) (P<0.05). Peak intracranial pressure in temporal and frontal were staggered arrangement.1.4 Peak strainPeak strain in Occipital, temporal and frontal increased with the hydraulic pressure (P<0.05). Peak strain in Occipital, temporal and frontal three parts were compared, peak strain in occipital was the numerical biggest (P<0.05), the temporal and frontal intracranial pressure size difference was not obvious (P>0.05).1.5 The cranial morphological changes of head impact experimentThe head specimen was scaned by CT after 0.73MPa hydraulic pressure impact experiment. And then scan data input mimics 15.0 for 3D reconstruction. A linear fracture was found through 3D reconstruction of skull after the experiment. The fracture line in herringbone stitch right 1cm to the skull base, slightly extended to the left.The fracture cracks widened after the 0.85MPa hydraulic pressure impact experiment. Two small pieces of free bone fragments about 1.5×0.8cm2 and 1×0.8cm2 were found at the left upper end and the right lower end.A few blocks comminuted fracture skull were found along the edge of linear fracture bone after the 0.9MPa hydraulic pressure impact experiment.The head specimen was dissected after the 0.95MPa hydraulic pressure impact experiment. A comminuted fracture, which contained a total of 10 pieces of fracture fragments, size from 1.2×0.3cm2 to 2.5×15.0cm2 range, was found in calvaria occipital by naked eye.2 Fall experiment2.1 Peak impact forceThe peak impact force increased ladder-like as the fall height increased. The biggest numerical value appeared at 1.8m height, then decreased.2.2 Peak intracranial pressureThe maximum intracranial pressure was in Occipital, followed by the frontal. The minimum was in temporal (except 1.8m group).2.3 Peak strainThe maximum strain was in occipital, followed by the frontal. The minimum was in temporal (P<0.05). In general, the three parts of strain values were increased with the increased of height in fall experiment.2.4 The cranial morphological change after the head fall experimentThe head specimen was scaned by CT after 0.73MPa hydraulic pressure impact experiment. And then scan data input mimics 15.0 for 3D reconstruction. A linear fracture was found through 3D reconstruction of skull after the experiment. The fracture line in herringbone stitch right 1cm to the skull base, slightly extended to the left.A linear fracture was found through 3D reconstruction of skull after the 1.3m height fall experiment. The fracture line was in the left margin of the occipital protuberance, extending to the left cranial bottom.The linear fracture gap slightly widen after the 1.6m height fall experiment. And it was above to the occipital protuberance about 1cm.The linear fracture gap was widened after 1.8m height fall experiment than before.The head specimen was dissected after 2.0m height fall experiment. A linear fracture was found from the left occipital to skull base, which was accord with the result of 3D reconstruction.Conclusion1、The head specimen fall from the height of 0-2m. The head was impacted with the steel plate under it. The skull fracture was linear fracture. The gap of fracture widen as the height increased. A linear fracture was found in occipital after the 0.73MPa hydraulic pressure impact experiment. A comminuted fracture was found in occipital after the 0.85MPa and 0.9MPa hydraulic pressure impact experiment. The fracture was more seriouse as the impact pressure increased.2、The acceleration and impact force increased with the height of fall increased. The acceleration increased with the increased of impact hydraulic pressure in the impact experiment. The impact force first increased and then decreased.3、The intracranial pressure in general was first increased and then decreased in fall experiment. Comparison of the three parts, the occipital intracranial pressure was maximum, followed by the frontal, and the temporal was minimum. As the impact test, the intracranial pressure in general was first increased and then decreased. Comparison of three parts, the intracranial pressure in occipital was maximum, followed by the frontal, and the temporal was minimum.4, The strain were increased not only in fall experiment but also in horizontal impact experimental. Comparison of three parts, in the level of impact test, the largest strain appeared inoccipital. No obvious difference was found between in frontal and temporal. In fall experiment, the strain in occipital was the largest, forehead secondly, temporal minimum.Chapter 2 THUMS Model 4.0 Used in the Research of Biomechanics Mechanism in Acceleration and Deceleration Head TraumaPurpose:Doing the research into fall and blow hurt of head with the human head finite element model THUMS4.0,so as to further the biodynamic mechanism difference of fall and blow hurt.Method:2.1 Horizontal hit experimentPlace the human head 3D dimension finite element model in a vertical situation. Use the circle plane of ion rod’s one end hit the occipital part of the head with 2.4m/s、3.4m/s、4.2m/s4.8m/s、5.4m/s、5.9m/s、6.4m/s、6.9m/s、7.3m/s、7.7m/s in sequence. Adopt face-to-face contact algorithm and choose the frontal、temporal、 parietal and occipital parts to analyze its peak stress、peak strain and peak cranial pressure. The consequence is put out into the form of data, picture and animation2.2 Fall experimentPlace the head in the different heights of 0.3m、0.6 m、0.9 m、1.2 m、1.5m、 1.8m、2.1 m、2.4 m、2.7 m、3.0 m in turn, make the head free fall from the a certain high altitude and let the occipital part hit the floor. In the same horizontal hit experiment use the frontal、temporal、parietal and occipital parts and analyze its peak stress、peak strain and peak cranial pressure. The consequence is put out into the form of data, picture and animation.Result1.1 Peak cranial pressureWith the increase of the hitting velocity, the cranial pressure was becoming higher and higher, and the hitting speed arrived at its peak of 5.9m/s(temporal part) or 6.4m/s,afterwards it became lower and lower. Under the same hitting velocity, the occipital part’s cranial pressure was the highest, the second was parietal part, the third was temporal part and the fourth was frontal part.1.2 Peak stressWith the increase of the hitting velocity, the peak stress was becoming higher and higher. The peak stress of the different hitting parts of the head aggregated at the velocity of 6.4m/s (frontal part)、6.9m/s (occipital and temporal part)'7.7m/s (parietal part). When it arrived at the speed of 6.9m/s, the frontal, parietal, temporal and occipital parts’peak stress grow in a decreasing trend. Under the same hitting velocity, the occipital part’s peak stress was the highest, then rank the frontal, temporal and parietal parts.1.3 Peak strainThe peak strain of the occipital part increased as the hitting speed grows at first, and it became stable when it arrived at the velocity of 4.8m/s to 6.9m/s, afterwards it decreased sharply. All the four parts don’t had an apparent strain process.2 Fall experiment2.1 Peak cranial pressureWith the falling altitude’s growing high, the peak cranial pressure of the head’s different parts aggregated at the falling height of 1.2m, then it grew in a decreasing tendency. Under the same hitting velocity, the occipital part’s peak cranial pressure is the highest, then rank the frontal, temporal and parietal parts.2.2 Peak stressThe peak stress of the occipital, temporal, frontal and parietal parts grew in an increasing tendency. Among the different parts, the occipital part ranked the first, the parietal part ranked the second, and the frontal and the temporal part’s difference was unapparent.2.3 Peak strainPeak strain increased as the falling altitude’s growing high at first, it arrived at its peak when it’s at the height of 1.8m, then it decreased sharply and maintain a stable level.Conclusion1. Horizontal hit experiment, with the hitting velocity’s growing fast, the peak cranial pressure increased first and then decreased.. Under the same hitting velocity, the occipital part’s cranial pressure was the highest, the second was parietal part, the third was temporal part and the fourth was frontal part. It accorded with the corpse head experimental conclusion.With the falling altitude’s growing high, the peak cranial pressure of the fall experiment increased first and then decreased. Under the same falling altitude, the peak cranial of the occipital part ranked the first, the frontal part ranked the second, the temporal part ranked the third and the parietal part rank the fourth. The conclusion accorded with the corpse head experimental trend. The hedge function had the capacity to amplify the peak cranial pressure. Several times’ falling in the same altitude had certain accumulation effect on head’s injury.2. As to the peak stress, in the horizontal hit experiment, with the growing fast of the hitting velocity, the peak stress increased first and then decreased. Under the same hitting speed, the occipital part’s stress was the biggest, the frontal part ranked the second, the temporal part ranked the third and the parietal part ranked the fourth.When it comes to the peak stress of the fall experiment, the occipital, temporal, frontal and the parietal part’s peak stress was growing in an increasing tendency. Among the different parts, the occipital ranked first, the parietal part ranked the second, and the difference between the frontal and the temporal part wasn’t unapparent. Apart from the occipital part, the peak stress of the parietal stress also ranked a relatively high level, it had some difference with the horizontal hit experiment.3. As to the strain, with the growing of the hitting speed, the peak stress of the horizontal hit experiment first increased, and it became stable when the hitting speed arrived in the range of 4.8m/s to 6.9m/s, then it decrease sharply. Peak strain of the fall experiment increased as the falling altitude’s growing high, and it decreased sharply when the falling altitude was 1.8m high, afterwards it maintained a low level stable state. When the peak strain of the occipital part in the horizontal and the fall experiment attained a certain value, both experimental peak strain decrease severely.The strain range is only limited in the occipital part, as the peri-bone suture broke, the strain change of the frontal, temporal and the parietal part couldn’t be checked.THUMS4.0 head finite element model horizontal hit experiment’s and fall experiment’s peak strain change almost accords with the experimental conclusion of the corpse head. The experimental conclusion of the corpse head can’s reflect the characteristic of the peak strain’s sharply decreasing.Chapter 3 Research on the Relationship between Blunt Impact ofRabbit s’Heads in Different Parts and Brain Injury Purpose:Carrying out research into rabbits’ head horizontal hit experiment, exploring the relationship between blunt impact of rabbit’s head’s different parts and brain injuryMethod:Put the adult healthy New Zealand big rabbits, both male and female, into occipital hurt、temporal hurt and parietal hurt groups at random, every group is 7 rabbits and the total is 21.During the experiment, place the rabbits in the hitting table with situation of positive recumbent position lateral recumbent position and negative recumbent position, make the head free, then use BIM-Ⅱ type bio-hitting machine to make the ion rod point parallelly to the rabbits’occipital、right temporal and parietal parts and hit them under 550kpa fluid pressure impact. Measure the cranial pressure of the rabbits’ parietal、right temporal and occipital parts. Record the vital signs of the rabbits’ post-hurt state. Calculate the instant death rate of the rabbits that in the post-hurt state.Result1.The instant death rate of the post-hurt rabbitsAfter hitting the different parts of the rabbits’head, their deaths rate had difference. The death rate of temporal part hitting ranked the first, occupied 42.86%, the occipital part ranked the second, possessed 28.7%, and the death rate of the parietal part hitting is the lowest2.The peak cranial pressure of the rabbits’different hitting partsWhen it hit the parietal part, the peak cranial pressure of the occipital part is higher than the left temporal part(P<0.05);when it hit the right temporal part, the peak cranial pressure of the left temporal was higher than the occipital part(P<0.01);when it hit the occipital part,the peak cranial pressure of the frontal part was higher than the left temporal part(P<0.01).From the data above, we can see that the peak cranial pressure of the occipital part is the highest when it hit,1647.43±81.71 kpa; then the peak cranial pressure of the left temporal part rank the second,1550.40±55.87 kpa。3.The analysis of cranial hurt due to the rabbits’different head part’s blowThe top injury group:6 cases of scalp hematoma,3 cases of fracture, mainly located at the top, temporal, middle cranial fossa,2 cases linear fracture,1 cases of annular fracture.4 rabbits with subdural hematoma.4 cases of subarachnoid hemorrhage.3 example skull haematoma.4 cases of brain contusion,3 cases of fracture with brain contusion.2 cases of brain contusion site at the top of the top blast injury, impact injury with skull base contrecoup injury in 1 cases,1 cases of skull base contrecoup injury.Right temporal injury group:3 cases showed scalp hematoma,5 cases with fracture, including 4 cases of linear fracture,1 cases of comminuted fracture.3 cases with subdural hematoma.5 cases of subarachnoid hemorrhage, were associated with fractures.1 case haematoma in skull base.5 cases of brain contusion,4 fracture cases with contusion of brain, and another 1 cases there was no fracture also see brain contusion.4 cases of shock right temporal brain contusion injury, with left temporal contrecoup injury in 1 cases.Occipital injury group:5 cases showed scalp hematoma,2 cases with linear fracture.4 cases with subdural hematoma. In 4 cases with subarachnoid hemorrhage, including 2 cases of fracture. A small amount of bleeding at the top,2 cases of skull base, the cerebellum is seen around the hemorrhage.3 see brain contusion, the occipital impact injury in 2 cases,1 cases of forehead contrecoup injury. Conclusion1. After hitting the different parts of the rabbits’head, their deaths rate have difference, the results from high to low in sequence are:temporal part (42.86%)>occipital part (28.7%)>parietal part (28.44%). The rabbits’death rates accord with cranial bone fracture、sub-arachoid space bleeding and brain contusion’s happening rate, but don’t have direct proportion with cranial pressure.2. Hitting different parts of the rabbits, the happening rates of cranial bone fracture from high to low in sequence are:temporal part> parietal part> occipital part.3. Hitting different parts of the rabbits, the happening rates of brain contusion from high to low in sequence are:temporal part>parietal part>occipital part.4. There are hedge injuries in all temporal、occipital and parietal hurt groups, but the happening rates are relatively low (parietal part 2/7、both right temporal and occipital part are 1/7)。Chapter 4BackgroundThe mechanical properties of 1-2-year-old pediatric cranial bones and sutures and their influential factors were studied to better understand how the pediatric calvarium reacts to loading.MethodsCranial bone and suture specimens were extracted from seven fresh-frozen human infant cadavers (1.5±0.5 years old). Eight specimens were obtained from each subject:two frontal bones, two parietal bones, two sag- ittal suture samples, and two coronal suture samples. The specimens were tested in a three-point bend set- up at 1.5 mm/s. The mechanical properties, such as ultimate stress, elastic modulus, and ultimate strain, were calculated for each specimen.ResultsThe ultimate stress and elastic modulus of the frontal bone were higher than those of the parietal bone (P<0.01 for ultimate stress and P<0.05 for elastic modulus). No differences were found between the coronal and sagittal sutures in ultimate stress, elastic modulus, or ultimate strain (P>0.05). The ultimate stress and elastic modulus of the frontal and parietal bones were higher than those of the sagittal and coronal sutures (both P<0.01), whereas the opposite ultimate strain findings were revealed (P<0.01).ConclusionsThere was no significant difference in ultimate stress, elastic modulus, or ultimate strain between the sagittal and coronal sutures. However, there were significant differences in ultimate stress, elastic modulus, and ulti- mate strain between the frontal and parietal bones as well as between the cranial bones and sutures.Summarization of Whole Thesis1、The fracture of skull could be formed by blow or by falling down. Cranial comminuted fractures could be formed by small plane objects in great force.2、The impact force, intracranial pressure, stress and strain would be changed by the skull fracture. The maximum numerical value of intracranial pressure, stress and strain is in the occipital in occipital impact and fall experiments.3、The three-dimensional finite element model of the skull could be used in the study of traumatic brain injury mechanism as the results of virtual experiments and body cadaveric specimens experiments were the same trend.4、The mortality of rabbits from high to low was as follows:temporal> occipital>parietal in different parts of rabbit skull impact experiments. The numerical order of mortality accord with the skull fracture, subarachnoid hemorrhage, cerebral contusion occurred’s. However, it was not accord with intracranial pressure size.5、In the building of infant brain finite element model, it should be assigned respectively between frontal bone and parietal bone, skull and suture in material properties. The coronal suture and sagittal suture could be regarded as homogeneous materials and assigned uniformly. |
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