UNIVERSIDADE ESTADUAL DE CAMPINAS
FACULDADE DE ODONTOLOGIA DE PIRACICABA
SÁRAH TEIXEIRA COSTA
PIRACICABA
2019
ANÁLISE DINÂMICA DE ELEMENTOS FINITOS DE
IMPACTO DE PROJÉTIL CALIBRE .40 S&W EM OSSO
TEMPORAL NA PRESENÇA DE TECIDOS NERVOSOS.
FINITE ELEMENT ANALYSIS DYNAMIC SIMULATION OF
PROJECTILE IMPACT CALIBER .40 S&W IN TEMPORAL
SÁRAH TEIXEIRA COSTA
ANÁLISE DINÂMICA DE ELEMENTOS FINITOS DE
IMPACTO DE PROJÉTIL CALIBRE .40 S&W EM OSSO
TEMPORAL NA PRESENÇA DE TECIDOS NERVOSOS.
FINITE ELEMENT ANALYSIS DYNAMIC SIMULATION OF
PROJECTILE IMPACT CALIBER
.40 S&W
IN TEMPORAL
BONE WITH NEURAL TISSUE.
Tese apresentada à Faculdade de Odontologia de Piracicaba da Universidade Estadual de Campinas como parte dos requisitos exigidos para obtenção do título de Doutora em Biologia Buco-Dental, na Área de Anatomia.
Thesis presented to the Piracicaba Dental School of the University of Campinas in partial fulfillment of the requirements for the degree of Doctor in Anatomy area.
Orientadora: Profa. Dra. Ana Cláudia Rossi
ESTE EXEMPLAR CORRESPONDE À VERSÃO
FINAL DA TESE DEFENDIDA PELA ALUNA
SÁRAH TEIXEIRA COSTA E ORIENTADA PELA
PROFA. DRA. ANA CLÁUDIA ROSSI.
PIRACICABA
2019
DEDICATÓRIA
Dedico este trabalho à minha mãe, Lígia, que nunca mediu esforços para
que eu alcançasse meus sonhos.
Dedico também este trabalho a minha tia, Rachel, e minhas avós, Petúnia
e Aparecida, que me apoiaram em absolutamente tudo.
Dedico também ao Rafael, mais que especial, um companheiro, amigo e
amor.
AGRADECIMENTOS
O presente trabalho foi realizado com apoio da Conselho Nacional de
Desenvolvimento Científico e Tecnológico (CNPq), processo nº 140976/2016-7.
À Universidade Estadual de Campinas, na pessoa do Magnifico Reitor Prof.
Dr. Marcelo Knobel.
À Faculdade de Odontologia de Piracicaba, na pessoa do Senhor Diretor,
Prof. Dr. Francisco Haiter Neto.
A Coordenadoria de Pós Graduação, na figura da Senhora Coordenadora
Prof. Dr.ª Karina Gonzalez Silvério Ruiz.
À Equipe Técnica da Coordenadoria de Pós-graduação nas pessoas de
Érica A. Pinho Sinhoreti, Raquel Q. Marcondes Cesar, Claudinéia Prata Pradella,
Leandro Viganó e Ana Paula Carone, agradeço pela paciência, atenção e
disponibilidade em sempre me ajudar.
Aos servidores da biblioteca da FOP-UNICAMP pela valiosa disponibilidade
e atenção.
Ao programa de pós graduação em Biologia Buco-Dental, na figura da
coordenadora Prof. Dr.ª Ana Paula de Souza.
A minha orientadora, Profa. Dra. Ana Cláudia Rossi, grande anatomista,
pelos seus conhecimentos a mim transmitidos, dedicação, paciência e amizade. Ela
não só apostou em um sonho como foi fundamental para sua concretização, abrindo
portas e dando grandes oportunidades. Serei eternamente grata pela confiança e
incentivo.
Ao Prof. Dr. Alexandre Rodrigues Freire, pela participação indispensável no
meu trabalho! Obrigada por ser um exemplo de seriedade e competência.
Aos professores Eduardo Daruge Junior, Felippe Bevilacqua Prado,
Roberta Okamoto e Marília de Oliveira Coelho Dutra Leal, por gentilmente aceitarem
o convite de participar da minha banca.
À minha mãe pelo apoio incondicional em todas as horas. Nada aconteceria
sem você!!
Ao meu irmão, Rafael, pelo apoio e união!
Ao meu noivo, confidente e amigo, pelo incentivo constante e compreensão
da minha ausência. Pelo alento no desespero e amor irrestrito.
Aos queridos Prof. Dr. Casimiro Almeida e Profa. Dra. Andreia Breda pelo
exemplo, carinho e valiosos ensinamentos.
Aos amigos de turma Marília Leal, Rafael Araújo, Marcos Paulo Salles
Machado, Larissa Lopes, Daniel Pignatari, Renato Takeo, Talita Máximo, Yuli
Quintero, Denise Rabelo, Tânia Santos, Rodrigo Ivo Matoso, Gilberto Carvalho, Talita
Lima e Thais Dezem, Viviane Ulbritch, Cristhiane Schimdt, Juliana Haddad, Maria
Cláudia Cuzzullin e Ana Paula Guidi, pois sem vocês tudo seria mais difícil.
Aos amigos Lívia Assis Lima, Enói Maria Miranda Mendes, Joana Panzera
de Souza Mello, Ana Guimarães de Brito Lira, Brunna Karla Lopes, Olívia Mara
Rodrigues, Cláudia D’Angelo, Débora Coelho, Marcela Romualdo, Andreia Queiroz,
Andrezza Albanese e Weslei Cavallaro, que mesmo depois da do colégio e graduação
sempre acompanharam minha trajetória.
A aqueles que mesmo de forma direta e indireta colaboraram com este
estudo.
RESUMO
Objetivo: O osso temporal é frequentemente atingido por projéteis. As feridas por
projétil de arma de fogo em osso temporal devem ser exaustivamente estudadas para
estabelecer a morfologia da ferida e a distribuição de tensões. A análise de elementos
finitos é uma ferramenta promissora que pode suportar aspectos forense. Já foram
realizados estudos balísticos pela análise de elementos finitos. Entretanto, todos
envolviam somente a simulação de tecidos ósseos. Até o presente estudo, restava
desconhecido se a presença de tecidos mole neural alteraria o resultado da análise.
Material e Métodos: A segmentação de estruturas anatômicas ósseas foi realizada
através do software Materialize MIMICS Research v. 18 (Materialize - Belgium) a partir
de dados de tomografia computadorizada de feixe cônico de um crânio seco. O
modelo tridimensional de elementos finitos do crânio seco preenchido com tecido mole
neural e projétil calibre .40 S&W de ponta plana foram obtidos pelo Ansys v17.2 e
Rhinoceros. Duas situações foram simuladas no Ansys v17.2. Tiros encostados
disparados a 90 ° com e sem tecido mole neural. Resultados: Os resultados mostram
diferentes morfologias nas lesões ósseas de entrada, bem como uma forte influência
dos tecidos moles. A distribuição de tensões e a perda de energia mostraram valores
mais altos na presença de tecido neural. Houve desvio no trajeto do projétil para baixo
com tecidos neurais. Houve boa reprodutibilidade entre o comportamento real do osso
e do tecido neural e o modelo de elementos finitos construído. Conclusão: A presença
de tecido mole neural não pode ser negligenciada, pois altera os resultados.
ABSTRACT
Aim: Temporal bone is often hit by projectiles. Temporal gunshot wounds must be
deeply evaluated in order to establish wound morphology and stress distribution. Finite
element analysis is a promising tool that can support forensic aspects. Ballistic studies
have already been performed by finite element analysis. However, all involved only the
simulation of bone tissues. Until the present study, it remained unknown whether the
presence of soft neural tissues would alter the outcome of the analysis. Material and
Methods: Segmentation of bone anatomical structures was performed in Materialize
MIMICS Research v. 18 (Materialize - Belgium) from cone beam tomography data of
a dry skull. Three-dimensional finite element model of the dry skull fulfilled with neural
soft tissue and projectile .40 S&W -caliber flat point were obtained in Ansys v17.2 and
Rhinoceros. Two situations were simulated in Ansys v17.2. Leaning shots fired at 90°
with and without neural soft tissue. Results: Results exhibit different morphologies in
entrance bony wounds as well as a strong influence of soft tissue. Von mises stress
distribution and energy loss showed higher values at the presence of neural tissue.
There was projectile deviation downwards with neural tissues. There was a good
reproducibility between bone and neural tissue real behavior and the finite element
model built. Conclusion: The presence of neural soft tissue cannot be neglected, since
it does alter results.
LISTA DE ILUSTAÇÕES
Figure 1. STL format (a) and meshes formed by tetrahedral elements (b).
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Figure 2. Ammunition 3D geometry.
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Figure 3. 3D model of impact scenario.
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Figure 4. Sagittal view of von Mises stress distribution with neural soft tissue.
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Figure 5. Sagittal view of von Mises stress distribution without soft tissue.
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Figure 6. External bony wound morphology with (a) and without neural tissue (b).
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Figure 7. Comparison between secondary lesions with neural tissue (a) and
without (b), in a sagittal view.
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Figure 8. Comparison between projectile deviation, with (a) and without (b) neural
LISTA DE TABELAS
Table 1. Properties of the materials used in the finite element models.
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Table 2. Results summrized comparing FEA with and without neural tissue.
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LISTA DE ABREVIATURAS E SIGLAS
CAD
-
Computer Aided Design
CBC
-
Companhia Brasileira de Cartuchos
Cu
-
Cobre
FEA
-
Finite Element Analysis
GPa
-
Gigapascal
MPa
-
Megapascal
NURBS
-
Non Uniform Rational B-Splines
Pb
-
Lead
q
-
Element quality
S&W
-
Smith and Wesson
STL
-
Stereolithographic
SD
-
Standard Deviation
Sb
-
Antimony
SUMÁRIO
1 INTRODUÇÃO
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2 ARTIGO
16
2.1 Artigo: Finite element analysis dynamic simulation of projectile impact caliber
.40 S&W in skull with neural tissue*
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3 CONCLUSÃO
28
REFERÊNCIAS *
29
ANEXOS
32
ANEXO 1: Verificação de originalidade e prevenção de plágio
32
ANEXO 2: Certificação do Comitê de Ética
33
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1 INTRODUÇÃO
A análise dinâmica de elementos finitos evoluiu, ao longo dos anos, para
modelos tridimensionais a fim de serem empregados na avaliação de acontecimentos
forenses, envolvendo, em especial disparos de arma de fogo (Huempfner-Hierl et al.,
2015; Costa et al., 2017). Diversos estudos foram realizados, tendo diferentes ossos
do crânio e região da face como alvos (Mota et al. 2003; Raul et al., 2007; Zhen et al.,
2012; Matoso et al., 2014; Pekedis e Yildiz, 2014; Costa et al., 2017; Rodrigues et al.,
2017), sendo que alguns destes estudos foram provenientes de nosso grupo de
pesquisa. Entretanto, a grande maioria dessas pesquisas trata dos efeitos da balística
interna e externa em tecidos ósseos.
Os tecidos moles possuem uma representação mais complicada que
tecidos duros, pois podem apresentar-se como não homogêneos e com propriedades
materiais plásticas e viscoelásticas não lineares (Guan et al., 2014). Há uma lacuna
do saber no que concerne à influência direta da presença de tecidos moles humanos,
como as condições clínicas e morfologia da ferida, bem como nos elementos balísticos
como a trajetória do projétil, perda de energia e velocidade.
O osso temporal é comumente alvo de projéteis de arma de fogo (Souza et
al. 2013). Feridas de arma de fogo no osso temporal apresentam um desafio referente
a motivação: homicídio ou suicídio. Parâmetros técnico científicos são essenciais para
definir a situação que levou à morte de um indivíduo. Raul et al. (2007) utilizaram a
análise de elementos finitos para auxiliar em investigações de um suicídio, com fortes
suspeitas de homicídio. Havia três ferimentos de entrada, causadas por um projétil
calibre .22, sendo um no peito (região do esterno), outro entre os olhos, no osso
frontal, e um orifício no osso temporal direito. A análise de elementos finitos foi
imprescindível para determinar a causa mortis como sendo suicídio, uma vez que o
único ferimento incompatível com a vida fora representado por aquele em que o alvo
fora o osso temporal. Os outros não lesaram estruturas vitais tampouco geraram
comorbidades cerebrais significativas.
Por conseguinte, devido à falta de dados concretos e confiáveis no que
concerne à presença de tecidos neurais, o presente estudo teve por objetivo comparar
simulações de análise dinâmica de elementos finitos, com e sem tecidos nervosos,
em que o osso temporal é alvo de projéteis de arma de fogo de calibre .40. A análise
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dos resultados das feridas de entrada e saída, com a presença de tecido mole neural
interposto levanta a hipótese nula de que os tecidos moles interferem em parâmetros
como o diâmetro da ferida, velocidade e perda de energia.
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2 ARTIGO
2.1 Artigo: Finite element analysis dynamic simulation of projectile impact
caliber .40 S&W in skull with neural tissue*
*O artigo foi submetido para apreciação no periódico internacional: International
Journal of Legal Medicine (ANEXO 3)
ABSTRACT
Aim: Temporal bone is often hit by projectiles. Temporal gunshot wounds must be deeply evaluated in order to establish wound morphology and stress distribution. Finite element analysis is a promising tool that can support forensic aspects. Ballistic studies have already been performed by finite element analysis. However, all involved only the simulation of bone tissues. Until the present study, it remained unknown whether the presence of soft neural tissues would alter the outcome of the analysis
.
Material and Methods: Three-dimensional finite element model of a dry skull fulfilled with neural soft tissue and projectile .40 S&W -caliber were obtained. Two situations were simulated. Leaning shots fired at 90° with and without neural soft tissue. Results: Results exhibit different morphologies in entrance bony wounds as well as a strong influence of soft tissue. There was a good reproducibility between bone and neural tissue real behavior and the finite element model built. Conclusion: The presence of neural soft tissue cannot be neglected, since it does alter results.Keywords: Finite element analysis; Neural soft tissue; Projectile; Morphology; Skull Biomechanics; Temporal bom; Gunshot wounds.
INTRODUCTION
Firearm projectile target can reveal important forensic aspects. Brazilian reality evidence that the temporal bone is the second bone most affected by firearm projectiles, reaching the target in a penetrating way or inclined [1]. The angle that gun is held to the head influences crime scene reconstruction, especially when concerns differentiation between homicide and suicide [2]. Usually, slanted wounds are related to homicides. Technical scientific parameters are essential to define the situation that led to the death of an individual.
Finite element analysis has become an effective analytical tool for skull biomechanics research [3]. Finite elements analysis is favorable for mechanical parsing, due to the production of reliable results in reduced time, excellent reproducibility and low experimental costs, allowing a control of the experimental conditions [4].
The finite element analysis was used to support suicide investigations with strong suspicions of homicide [5]. There were three entry wounds, caused by a .22 caliber projectile, one in the chest (sternum region), the other between the eyes in the frontal bone, and a hole in the right temporal bone. The finite element tool was essential to determine the cause of death as suicide, since the only injury incompatible with life was represented by the one in which the target was the temporal bone. The others did not damage vital structures, nor did they generate significant cerebral comorbidities [5].
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Although finite element analysis is a promising tool, there are still some limitations to overcome. The use of soft tissues in the simulation is an obstacle, since their absence may change the results and consequently alter reproducibility [6–9]. Some discrepancies between the results and the actual conditions may be due to the methodologies frequently used in previous analyzes containing only bony tissues [10]. The interaction of the projectiles probably promotes a dissipation and absorb energy from the impact, reducing the diameter of the wound [8].
Several studies regarding bony tissues and finite element analysis were developed [3–6, 11– 18]. Nevertheless, the behavior of the neural tissue model has been controversial, with the investigation of mechanical properties of soft tissues as the brain, the focus of recent efforts [19].
It is explicit the need for a dynamic study of the injuries produced by firearm projectiles, including the presence of soft tissues, through the analysis of finite elements. The possibility to predict or simulate firearm projectiles effect on the bone structure and nervous tissues at the most diverse circumstances allows a good forensic context comprehension.
The purpose of the present study was to evaluate the hypothesis that soft tissues would change morphology, energy loss, stress distribution of the bony wound and projectile deformation, fragmentation and deviation.
MATERIALS AND METHODS
The Committee for Ethics of Research of the University of Campinas (CAAE number: 66180717.5.0000.5418) approved this study.
Samples and images acquisition
A dry skull, in good state of preservation, with morphology of the anatomical structures preserved, qualitative morphological characteristics typical of a young adult male, without macroscopic visible bone pathologies was randomly chosen, according to previously studies from our research laboratory group [12, 18]. Bone surface images of the human skull were acquired using computed tomography scans (GE HiSpeed NX/i CT scanner, General Electric, Denver, CO) at a 0.25-mm slice thickness.
The chosen ammunition was .40-caliber S&W, full metal jacket with flat point, because it is employed by state military police officers and civil police officers in Brazil. Projectile specification was acquired according to data provided by a Brazilian manufacturer of weapons and ammunition (Companhia Brasileira de Cartuchos, CBC, Ribeirão Pires, Brazil) [11]. Projectile .40-caliber has a muzzle velocity of 300 m/s, mass of 11,66 g and 524 J of kinetic energy.
Bone and neural soft tissue tridimensional model construction
Segmentation of bone anatomical structures was performed in Materialise MIMICS Research v. 18 (Materialise - Belgium) from cone beam computed tomography data. The anatomical structures of interest were segmented, forming a three-dimensional polygonal surface of the bone structure.
The space present in the intracranial cavity was filled in the segmentation to form a three-dimensional surface corresponding to the tissues of the central nervous system in this region. Neural
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soft tissue was simplified. Internal cranium anatomical structures were not distinguished. Grey and white matter, cerebellum, ventricles, corpus callosum, thalamus were considered as one homogeneous material. Neural soft tissue was considered as linear and elastic.
The surfaces (bone and neural soft tissue) were exported in stereolithographic format (STL) (Figure 1) and converted into volumetric meshes formed by tetrahedral elements using the software 3-MATIC v.10 (Materialise - Belgium).
The cranium final model with neural soft tissue presented 3,334,185 elements and 608.111 nodes, while without any soft tissue there was 638,830 and 136.514 elements and modes, respectively. Element quality (q) has the highest score at q=1. Our study revealed an excellent score set at q=0.83 (SD = + 0.1).
Figure 1. STL format (a) and meshes formed by tetrahedral elements (b).
Ammunition Model Construction
The ammunition model (.40-caliber S&W) (Figure 2) were constructed with free-form non-uniform rational B-spline (NURBS) surfaces using a reverse engineering method [4] in the 3D software Rhinoceros 5.0 (McNeel & Associates, Seattle, WA).
Figure 2. Ammunition 3D geometry.
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Simulations of projectile impact on the temporal bone were made by an explicit dynamics’ analysis through the solver AUTODYN, using the Ansys v17.2 software (ANSYS, Cannonsburg, PA, USA). All data were processed by the solver using an Intel Xeon E5-2630v3 2.40 GHz processor, 24 GB random-access memory and video card NVIDIA Quadro K2200 (2 GB memory) to perform the analysis. Materials properties used in this research were collected in Matweb and previous studies [13, 19, 20]. Data is in Table 1.
Table 1. Properties of the materials used in the finite element models. Properties Human Bone
a Neural soft tissue .40 S&W-caliber Jacket Cu b Core Pb (99%) / Sb (1%) c Young’s modulus (GPa) 14 10 115 14 Poisson’s ratio 0,3 0.45 0.3 0.38 Shear modulus (GPa) 5.3846 3.4 46 8,6
Bulk modulus (GPa) 11,667 3.3 129 - Density (Kg/m3) 1850 1041 8960 11340 Specific heat (J/Kg.uC) 440 - 383 124
Tensile Stress failure (GPa)** 0.133 - - - Shear Stress failure(GPa) ** 0.067 - - - a Wroe et al [20].
b Copper (Cu) alloy UNSC23000 [11]
c 99%Lead (Pb)/1%Antimony (Sb) alloy UNSL52605 [11]. d Copper (Cu) alloy UNSC22000 [11]
**MatWebDatabase.
Two simulations for .40-caliber S&W ammunition was performed (Figure 3): (i) Shot was fired with gun barrel leaning on temporal bone area at 90°; (ii) Shot was fired with gun barrel backboard on temporal bone area at 90° and cranium filled with neural soft tissue. In order to get precision, tetrahedral elements of the target area were reduced, refining mesh at this zone. Only gravity was specified. Effects caused by air resistance, yaw, precession, and nutation were not considered because of the backboard shooting [11, 12]. In one of the simulations, skull cavity was filled with tissue with brain properties.
Boundary conditions were settled along three axes (x,y,z) in the occipital condyles area, at the joint of the first cervical vertebra and at regions of insertion of the cervical muscles, in occipital bone and mastoid process [18, 21]. These conditions provide skull stability under in vivo conditions; hence it was simulated in the present study.
Analysis of Results
Results were analyzed according to von Mises stress distribution, kinetic energy dissipated, bony wound morphology and projectile deformation, fragmentation and deviation.
Von Mises stress distribution was evaluated in MegaPascal (MPa), whose values will be distributed in color intervals in a scale configured by Ansys v17.2 (CA, Pennsylvania, USA).
The Ansys v17.2 software was also used for the simulation that provided impact velocity and residual velocity, meaning that pre- and post-collision kinetic energy were calculated to investigate the degree of damage, in both simulations. The difference between post kinetic energy and pre kinetic energy provides estimation on wounding capacity and damage efficiency [12, 18].
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Finite element tridimensional model of temporal bony wound morphology, with neural tissue, was evaluated through Image J software (National Institute of Health – NIH, USA). Measurements consisted of maximum diameter as well as total area [18]. Measurements accuracy were calculated using the intra-class coefficient (ICC) on Bioestat 5.3 software (Instituto Mamirauá, Brazil) [18].
Figure 3. 3D model of impact scenario.
RESULTS
Results comparing FEA with and without neural tissue are summarized in table 2, and then explained according to each parameter analyzed.
Table 2. Results summrized comparing FEA with and without neural tissue.
Parameter FEA without neural tissue FEA without neural tissue Von Mises stress
distribution
Higher stress distribution at the left orbit, some regions of zygomatic arch, maxilla, front-zygomatic suture, sphenoid lesser wing and Sella turcica
Smaller values of stress distribution at the left orbit, some regions of zygomatic arch, maxilla, front-zygomatic suture, sphenoid lesser wing and Sella turcica
Energy loss 194,465.5 J: Higher values 50,955.46 J: smaller values Bony wound
morphology
Larger wounds and the presence of secondary wounds at the superior wall of the orbit at the left side
Smaller wounds and no secondary wounds
Projectile deformation Larger deformations Smaller deformations Projectile
fragmentation
No projectile fragmentation No projectile fragmentation
Projectile track deviation
Projectile track deviation downwards
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Von Mises stress distribution
Around the ballistic impact area on temporal bone, higher stress distribution was observed. High values were also found in the left orbit and some regions of zygomatic arch, maxilla and front-zygomatic suture. In addition, sphenoid lesser wing and Sella turcica region also exhibited higher values of von Mises stress.
Von Mises stress distribution was higher at the presence of neural soft tissue around the ballistic impact area (Figure 4). Without soft tissue von Mises stress distribution was more scattered (Figure 5).
Figure 4. Sagittal view of von Mises stress distribution with neural soft tissue.
Figure 5. Sagittal view of von Mises stress distribution without soft tissue.
Energy loss
Energy loss of projectile, calculated through the difference between pre and post collision, using impact and residual velocity, with and without neural soft tissue was, respectively, 194,465.5 J and 50,955.46 J. In other words, the projectile had lost 37.06% of total kinetic energy in the presence of neural soft tissue, whilst without soft tissue, the lost was only 9,9%.
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Bony wound morphology produced by a .40-caliber S&W fired perpendicular on temporal bone with neural soft tissue presented a round aspect with a maximum diameter of 22.38 mm and total area of 250.49 mm2. The same situation but simulated without neural soft tissue presented a more regular round shape with a maximum diameter of 19.48 mm and total area of 227.92 mm2 (Figure 6). Maximum diameter and total area got excellent intraclass correlation (ICC=0.9, p˂0.0001)
Figure 6. External bony wound morphology with (a) and without neural tissue (b).
Secondary wounds could be observed at the superior wall of the orbit at the left side (entrance wound) when neural soft tissue is present (Figure 7).
The external surface of the temporal bone presented a surface area that was larger than the internal one, creating an internal beveling, in both simulations. Therefore, there was greater internal diploe bone destruction.
Figure 7. Comparison between secondary lesions with neural tissue (a) and without (b), in a sagittal view.
Deformation, fragmentation and deviation
The presence of neural soft tissue led to an extensive deformation of the projectile tip. But at any circumstances there was not a projectile fragmentation nor metal jacket detachment.
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After entrance wound generation, .40 S&W–caliber described a different trajectory in both situations. At the absence of neural soft tissue, projectile trajectory was linear. On the other hand, projectile trajectory bent over towards the cranial cavity floor, when neural tissue was present (Figure 8).
Figure 8. Comparison between projectile deviation, with (a) and without (b) neural tissue, in a coronal view.
DISCUSSION
Gunshot wounds can reveal much about crime scene circumstances. Since finite element analysis is biomechanical tool, computed simulation may rebuild some shooting aspects [14], as distance, angulation and direction [11].
Our group research [11, 12, 18], used the finite element analysis for simulation to study the bony morphology and stress distribution in gunshot wounds for forensic purposes. There are some issues that must be overcome in order to approach simulation to reality. Nowadays, the presence of soft tissues is an obstacle. Besides, there is no pattern regarding on which soft tissue must be represented on simulation. Studies have been made using finite element models with different types of soft tissue, such as cerebrum with grey matter, white matter and ventricles [14]; ballistic gelatin [22]; brain tissue [19]; skin, cerebrum, cerebellum, lateral ventricles, corpus callosum, thalamus and brainstem [23]; layer of skin and muscle [21] and scalp [24]. The present study considered all neural soft tissue as a homogeneous material.
Neural soft tissue role in gunshot wound is unsettled. The presence of soft tissues might play a dissipative role and absorb some of the energy from the impact. Energy absorption can lead to a wound dimeter reduction [10]. On the contrary of what was presumed by Stefanopoulos (2013) [10], in our research, the presence of neural soft tissue led to entrance wounds with greater diameter. But this difference was not significant visually. Parallelly, a head to head accidental with a skin and muscle layer impact was simulated [21]. Data disclose that the presence of soft tissue (skin and muscle) did not play a decisive role, suggesting that soft tissue can be neglected on simulation, since does not differ on
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results [21]. Our results demonstrated that the presence of neural soft tissue does matters, not at entrance gunshot wound diameter, but at other issues, such as von Mises stress distribution, energy loss and projectile deformation, deviation and fragmentation. Simultaneously, larger secondary lesions appeared at the superior wall of the orbit. In addition, von Mises stress distribution also presented higher values at left sphenoid lesser wing and Sella turcica region.
The greater entrance wound diameter at the presence of neural soft tissue could be explained by forces that came from projectile impact at the bony tissue absorbed by neural tissue. The presence of neural tissue filling cranial cavity might exhibited reverse force vectors that react with the inner diploe against the forces originated from the projectile, therefore increasing the external beveling surface of the entrance wound. The same explanation can be applied to the secondary wounds at the superior wall of the orbit, since the absorbed forces was dissipated to closer structures. Hence, the amount of neural soft tissue that was presented below the projectile trajectory was thinner than the superior one, the resulted force distribution was stronger downwards.
Higher values of von Mises stress distribution in the presence of neural soft tissue at anterior cranial fossa and middle cranial fossa could be used to explain causa mortis and wound damage degree. Sphenoid lesser wing and Sella turcica regions are the bony floor of noble and vital structures. Concerning blood supply, there are cavernous sinus and the circle of Willis. The first, second and third cranial nerves, known respectively as olfactory, optic and oculomotor nerves could also be seriously damaged.
Inner beveling is a typical sign of gunshot entrance wounds [7]. Our results recreated the typical beveling morphology, establishing a good parameter between bone real behavior and the virtual one, represented by finite element analysis.
Full metal jacket projectiles are less susceptible to fragmentation. Thereafter, we considered that changes in the mass of the projectile were negligible when calculating energy loss. Although there was no fragmentation, there was a big projectile deformation. Ammunition .40 - caliber S&W flat point has a larger bone surface contact, leading to a greater energy loss. The presence of neural soft tissue increased the final amount of energy loss, therefore, more deformation occurred.
Neural soft tissue also influenced projectile trajectory. Entrance wound at temporal bone is closer to cranial cavity floor than to inner cranial roof, formed by parietal and frontal bones. Therefore, there was a greater amount of neural soft tissue above, deflecting projectile downwards. This phenomenon could also explain the extensive secondary lesions at superior wall of the orbit and higher von Mises stress at left sphenoid lesser wing and Sella turcica region. Besides, this trajectory deflection could also modify the position of the exit wound.
CONCLUSION
The presence of neural soft tissue in the cranium displayed a difference in gunshot simulation regarding energy loss, stress distribution, projectile deformation, fragmentation and deviation. Thus, for forensic purposes, the presence of neural soft tissue cannot be neglected. Clinical implications must be studied separately.
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COMPLIANCE WITH ETHICAL STANDARDS
Disclosure of potential conflicts of interest
Funding: The first author (Costa, ST) was funded by National Council for Scientific and Technological Development -CNPq (grant number 140976/2016-2017)
Conflicts of interests: The authors declare that they have no conflict of interest
Research involving human participants
Ethical approval: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee (The Committee for Ethics of Research of the University of Campinas - CAAE number: 66180717.5.0000.5418) and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.”
Informed consent
Informed consent was not obtained, since the images from skull included in the study is in Anatomy Laboratory for decades. It was not possible to reach relatives as well.
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FIGURE CAPTIONS
Fig 1 STL format (a) and meshes formed by tetrahedral elements (b) Fig 2 Ammunition 3D geometry
Fig 3 3D model of impact scenario
Fig 4 Sagittal view of von Mises stress distribution with neural soft tissue Fig 5 Sagittal view of von Mises stress distribution without soft tissue
Fig 6 External bony wound morphology with (a) and without neural tissue (b)
Fig 7 Comparison between secondary lesions with neural tissue (a) and without (b), in a sagittal view Fig 8 Comparison between projectile deviation, with (a) and without (b) neural tissue, in a coronal view
