【作者】 唐震；

【导师】 谭颖徽；

【作者基本信息】 第三军医大学 ， 外科学， 2011， 博士

【摘要】 颌面部位置暴露,战时防护薄弱,和平时也是暴力、自伤的重点部位,在全身火器伤的发生中,颌面部火器伤所占比例较大。因此,颌面部火器伤的救治是颌面部乃至全身创伤救治中的重点问题。目前用于创伤弹道学研究的颌面部传统火器伤模型仍然以动物模型为主,辅以尸体及人工材料模型。然而,由于可重复性差以及目前陪受关注的医学伦理方面的原因,动物及尸体模型的应用受到很大限制。人工材料模型虽然具有与人体组织相近的生物力学性质。但其制作成本高,费时长。随着社会和科学技术的发展,这些模型已越来越显露出其局限性,因此,我们需要采用新的方法来建立更加理想的致伤模型。有限元法又称有限元分析法(Finite Element Analysis,FEA)或有限元素法(Finite Element Method,FEM),是在工程科学技术领域广泛应用的数理方法。有限元法的基本原理是把整个结构看作由有限个细小单元组合而成的实体,整体的力学特性是由每个个体单元的力学特征叠加整合后反映出来,最常用于解决复杂的工程学问题,目前已广泛应用于生物力学研究中。有限元法能够分析物体内及物体间的复杂力学过程,预测力学作用产生的效应(如模型的应力、应变、形状、温度等的变化),并且能够在电脑上直观显示或输出计算结果以供分析,具有可重复性好、节约实验成本、实验条件易控制等优点,可以弥补传统的火器伤模型在致伤过程研究中的不足。因此,有限元法的运用将有助于颌面部火器伤致伤机理的深入研究,并能为颌面部火器伤致伤部位伤情的快速判断、火器伤的迅速救治、战时的防护以及评估投射物致伤效应等等提供新的思路和方法。本研究以前期建立的猪下颌骨火器伤有限元模型为基础,采用经动物实验验证的有限元模型内置参数,建立了可视化数字人上、下颌骨火器伤三维有限元模型,用有限元方法动态模拟不同投射条件下投射物侵彻人上、下颌骨的过程,并对人上、下颌骨火器伤的生物力学机制进行了初步探讨。研究方法和结果:1.将中国可视化数字人(Chinese Visible Human, CVH)头面部计算机X射线断层扫描(Computed Tomography,CT)数据导入MIMICS软件中,经过三维图像获取、实体模型重建后得到人上、下颌骨面网格模型;将上、下颌骨面网格模型导入ANSA软件中,采用六面体单元与五面体及四面体单元结合的方式建立人上、下颌骨火器伤三维有限元模型。建立的人上颌骨三维有限元模型的单元数为372501,节点数为751410;下颌骨三维有限元模型的单元数为275216,节点数为1387101,所有单元均为实体单元。结果表明,该模型网格划分合理,单元质量好,与真实标本的几何外形相似程度高,细节损失小。2.在前期动物实验建模的基础上,选择适合的材料模型、生物力学参数、边界条件及接触算法,对所建立的人下颌骨火器伤三维有限元模型加载不同的入射条件(两种投射物、两个投射部位、三个入射角度及三种入射初速度),在LS-DYNA软件中进行仿真计算,动态模拟人下颌骨火器伤的致伤过程、应力传导及分布的情况。结果表明,本研究所建立的人下颌骨火器伤三维有限元模型几乎全采用六面体单元建模,满足了多个投射物多角度多部位打击下颌骨的研究需要,并提高了计算精度。不仅可以动态模拟不同入射条件下,下颌骨受打击的过程及损伤的严重程度,还可以观察投射物的运行轨迹及比较其投射效率;并且,通过对应力的计算,还可以动态模拟火器伤过程中应力在下颌骨中传导的方式及各部位应力随时间分布的情况。3.采用与下颌骨相同的材料模型、生物力学参数及接触算法,设定适合的边界条件,对所建立的人上颌骨火器伤三维有限元模型加载不同的入射条件(一个入射角度、两种投射物、两个投射部位及三种入射初速度),在LS-DYNA软件中进行仿真计算,动态模拟人上颌骨火器伤的致伤过程、应力传导及分布的情况。结果表明,本研究所建立的人上颌骨火器伤三维有限元模型采用四面体单元、五面体单元与六面体单元结合的方式建立人上颌骨三维有限元模型,在兼顾了计算效率和计算精度的基础上,降低了建模成本及运算时间,可以动态模拟不同入射条件下上颌骨受打击的过程及损伤的严重程度,还可以动态模拟火器伤过程中应力在上颌骨及颅底中传导的方式及各部位应力分布随时间的变化情况。结论:1.成功建立了人上、下颌骨火器伤三维有限元模型,该模型细节部分网格划分十分理想,细节损失小,几何相似程度高;各项网格单元质量检查结果均达到设定的检查标准,网格单元尺寸较均匀;装配后的上、下颌骨火器伤有限元模型符合动态模拟要求。2.在以下颌角及颏部正中为入射点,且入射角度限定在45°至90°之间时,下颌骨火器伤的致伤特点是:1)、入射角度越小,下颌骨受损伤的程度越重,投射物的致伤效率也越高;2)、入射初速度越大,下颌骨受损伤的程度越重,但投射物的致伤效率却越低;3)、钢珠的致伤效率远高于子弹,而子弹对下颌骨的损伤程度可能在大多数情况下均大于钢珠,但在入射角度接近于90°时,随着入射初速度的增加,钢珠对下颌骨的损伤程度可能大于子弹;4)、投射物在下颌角部位入射时对下颌骨造成的损伤程度及致伤效率均大于颏部正中入射;5)、在下颌骨的火器伤发生时,击入侧髁状突颈部发生骨折的可能性较大;6)、距离下颌骨伤道越近,应力在该部位分布越集中。3.在以上颌骨侧面的前点及后点入射,且入射角度与矢状面垂直时,上颌骨火器伤的致伤特点是:1)、在上颌骨前点入射时投射物对上颌骨造成的损伤及致伤效率略大于上颌骨后点入射;2)、入射初速度越大,上颌骨受损伤的程度越重,但投射物的致伤效率却越低;3)、子弹对上颌骨造成的损伤大于钢珠,但其致伤效率却小于钢珠;4)、投射物以相同的初始动能入射时,钢珠对上颌骨造成的损伤及致伤效率均大于子弹;5)、距离上颌骨伤道越近,该部位所受应力越强;6)、上颌骨火器伤时伴发颅脑损伤的严重程度与枪弹的入射部位及投射物的性质有关,与投射初速度的相关性小。4.我们建立的人上、下颌骨火器伤三维有限元模型可以进行颌面部火器伤生物力学研究。在研究颌面部火器伤生物力学机制方面,有限元方法可以弥补传统火器伤研究模型的不足。更多还原

【Abstract】 The maxillofacial region is an exposed part of the body and a common location of firearm wounds, including both self-inflicted injuries and injuries caused by others. The firearm wounds of the maxillofacial region have a much higher ratio than the other parts of human body. So, it is very important to focus on trauma salvage and treatment of maxillofacial firearm wounds. The traditional injury models of firearm wounds include animal models, human cadaver models, and models that are made of artificial materials. However, the applicability of animals and human cadavers has been greatly limited due to poor reproducibility and current medical ethics concerns. The artificial material models possess biomechanical properties that are similar to human tissues, but they have high production costs and long production times. Therefore, it is desirable to develop an improved injury model using novel methods.The Finite Element Method (FEM) is a mathematical method that has been widely used in engineering science and technology. The principle of FEM is that a whole structure is assembled by many finite tiny elements, and the whole mechanical characters of structure are contributed by every elements. FEM has become an effective analytical tool for solving complicated engineering problems and widely used in different areas of biomechanics research.FEM can analysis the complicated mechanical processes among or inside the body and predict the effect of mechanical action (just like the change of shape, stress, strain, temperature and so on). It may offer the possibility to precisely measure the amount of energy or force and display the result. Moreover, FEM has the advantages of good repeatability, low cost and manageable load conditions, which makes up for the insufficiency of other firearm wounds models. Therefore, FEM will conduce to deeply researching in vulnerate mechanism of firearm wounds in the maxillofacial region.Based on our previous three-dimensional finite element (3D FE) model of firearm wounds in the pig mandible and the internal parameters of the model, we established a 3D FE model of firearm wounds to the maxilla and mandible of Chinese Visible Human (CVH). By using this model, we dynamically simulate the mechanical process of maxilla and mandibular firearm wounds in different injury conditions and investigate the preliminary biomechanical finite element analysis of the progress.Methods and Results:1. Computed Tomography (CT) data of Chinese Visible Human maxilla and mandible was imported into MIMICS software, where the three-dimension computer-aided designing surface mesh models of human maxilla and mandible were reconstituted. These surface-meshed models of the maxilla and mandible were then imported into ANSA software for automatic net-generation and then the combined hexahedral, pentahedral and tetrahedral element FE models of human maxilla and mandible were established. The final model of the maxilla was meshed with 372,501 entity elements and 751,410 nodes; the final model of the mandible was meshed with 275,216 entity elements and 1,387,101 nodes. The results showed that the FE models posessed reasonable partitioning meshes and good-quality elements, and the FE models were similar to the human anatomical structure.2. Based on our previous 3D FE model of firearm wounds in the pig mandible, we selected compatible material model, internal parameters, boundary condition and algorithm of contact in LS-DYNA software. After computation of simulation, the established 3D FE model of firearm wounds to the human mandible dynamically simulated the mechanism of mandibular firearm wounds and the stress distributions in its various regions under different injury conditions. The results showed that hexahedral elements were used almost exclusively for the mandible 3D FE model to obtain greater computational precision and meet the need of research in different injury conditions. The finite element model can dynamically simulate the injury mechanisms of firearm wounds to the human mandible. By comparing and analyzing the related data, the injury severity of the mandible and the injury efficiency of the projectiles could be investigated under different injury conditions. Moreover, we can also dynamically simulate the process of the stress spreading and the stress distribution patterns in each region of the mandible affected by the firearm wounds.3. Just like the 3D FE model of human mandible, we seted the same material model, internal parameters, algorithm of contact and compatible boundary condition in LS-DYNA software. After computation of simulation, the established 3D FE model of firearm wounds to the human maxilla dynamically simulated the process of maxillary firearm wounds and the stress distributions in its various regions using bullet or steel ball shots with varying velocities and entry position. The results showed that hexahedral, pentahedral and tetrahedral elements were used for the maxilla 3D FE model to obtain better computational efficiency and computational precision, cutting down the cost of model establishment and the time of computation. The finite element model can dynamically simulate the injury process of firearm wounds to the human maxilla. The injury severity of the maxilla could be investigated under different injury conditions. Moreover, we can also dynamically simulate the process of the stress spreading and the stress distribution patterns in each region of the maxilla and bases of skull affected by the firearm wounds.Conclusions:1. The 3D FE models for firearm wounds in the human maxilla and mandible were successfully established. The FE models of the human maxilla and mandible were similar to the real anatomical structure and had perfect meshes and elements. The quality of the mashes and elements had reached the level and the size of which were uniformity.The combined 3D FE models for firearm wounds in the human maxilla and mandible can meet the demand of dynamic simulation for biomechanical research.2. When the projectile’s entry angle limited to the range of 45°to 90°and the entrance points were in angle of mandible and in centric position of mental region, we can draw the following conclusions: 1). The smaller the entry angle was, the more severe injury was caused to the mandible and the higher injury efficiency was caused by the projectile. 2). The higher the impact velocity was, the more severe the injury was caused to the mandible but the lower the injury efficiency was caused by the projectile. 3). The injury efficiency of steel ball was much higher than that of bullet. However, the injury severity to mandible of bullet was higher than that of steel ball in most of the cases. If the entry angle was close to 90°, as the impact velocity increased, the injury severity to mandible of steel ball might be higher than that of bullet. 4). When the entrance point was in angle of mandible, the injury severity to mandible and the injury efficiency of projectiles were both higher than that of centric position of mental region. 5). When the mandible was shot by projectiles, the fracture of neck of condyle in shooting side was more common than other regions. 6). The nearer the region to the wound tract of the mandible, the more stress distributed to it.3. When the projectile’s entry angle was perpendicular to the sagittal plane and the two entrance points were in lateral side of maxilla, we can draw the following conclusions: 1). When the entrance point was in the forward place of maxilla, the injury severity to maxilla and the injury efficiency of projectiles were both higher than that of the backward place of maxilla. 2). The higher the impact velocity was, the more severe the injury was caused to the maxilla but the lower the injury efficiency was caused by the projectile. 3). The injury severity to maxilla of bullet was higher than that of steel ball, but the injury efficiency of steel ball were higher than that of bullet. 4). When the initial kinetic energies of the projectiles was the same, the injury severity to maxilla and the injury efficiency of steel ball were higher than those of bullet. 5). The nearer the region to the wound tract of the maxilla, the more stress distributed to it. 6). The injury severity of brain associated with firearm wounds in maxilla was related to the entry point and the nature of projectiles, but not related to the impact velocity.4、The 3D FE models could be used in investigation of biomechanical mechanism of firearm wounds in the maxillofacial region. When concerned with the investigation of biomechanical mechanism of wound ballistics, FEM can make up for the insufficiency of other traditional firearm wound models.更多还原