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PURPOSE: To compare instrumentation configurations consisting of bilateral single or double rods and additional interbody cages (IBCs) at different levels in terms of Range of Motion (ROM) and distribution of von Mises stress in rods. METHODS: A previously validated L1-pelvis finite element model was used and instrumented with configurations consisting of single or double bilateral rods and IBCs at multiple levels. Pure moments of 7.5 N.m were applied to L1 in main directions in addition to a follower load of 280 N. Global, segmental ROM and distribution of von Mises stress in rods were studied. RESULTS: All configurations reduced segmental and global ROM from 50 to 100% compared to the intact spine. Addition of IBCs slightly increased ROM at levels adjacent to the IBC placement. The simple rod configuration presented the highest von Mises stress (457 MPa) in principal rods at L5-S1 in flexion. Doubling rods and IBC placement reduced this value and shifted the location of maximum von Mises stress to other regions. Among studied configurations, double rods with IBCs at all levels (L2-S1) showed the lowest ROM. Maximal von Mises stresses in secondary rods were lower in comparison to main rods. CONCLUSIONS: Double rods and IBCs reduced global and segmental ROM as well as von Mises stress in rods. The results suggest a possible benefit in using both strategies to minimize pseudarthrosis and instrumentation failure. However, increased ROM in adjacent levels and the shift of maximal von Mises stress to adjacent areas might cause complications elsewhere.
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Vértebras Lombares , Fusão Vertebral , Fenômenos Biomecânicos , Análise de Elementos Finitos , Humanos , Vértebras Lombares/cirurgia , Amplitude de Movimento Articular , Fusão Vertebral/métodosRESUMO
Violently shaking a baby leads to clinical presentations ranging from seizures to cardiopulmonary arrest. The main injuries sustained are retinal hemorrhages, subdural hemorrhages, and sometimes fractures and spine injury. It is important to have a global view of the injuries sustained by the infant to correctly discuss the biomechanical aspects of abusive head trauma. Recent works based on finite element models have shown that whiplash-shaking alone is enough to generate vitreo-retinal traction leading to retinal hemorrhage and to cause the rupture of bridging veins leading to subdural hemorrhage. We will review the main papers dealing with the mechanisms of shaken baby syndrome and present the most relevant hypothesis concerning the biomechanical aspects of injuries related to shaken baby syndrome.
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Encéfalo/fisiopatologia , Maus-Tratos Infantis/prevenção & controle , Hemorragia/fisiopatologia , Síndrome do Bebê Sacudido/fisiopatologia , Traumatismos da Medula Espinal/fisiopatologia , Fraturas da Coluna Vertebral/fisiopatologia , Feminino , Medicina Legal/métodos , Hemorragia/etiologia , Humanos , Lactente , Recém-Nascido , Masculino , Modelos Biológicos , Síndrome do Bebê Sacudido/complicações , Traumatismos da Medula Espinal/etiologia , Fraturas da Coluna Vertebral/etiologia , Estresse MecânicoRESUMO
Individuals exposed to the propagation of shock waves generated by the detonation of explosive charges may suffer Traumatic Brain Injury. The mechanism of cranial deflection is one of many hypotheses that could explain the observed brain damage. To investigate this physical phenomenon in a reproducible manner, a new simplified cranial substitute was designed with a mechanical response close to that of a human skull when subjected to this type of loading. As a first step, a Finite Element Model was employed to dimension the new substitute. The objective was indeed to obtain a vibratory behavior close to that of a dry human skull over a wide range of frequencies up to 10 kHz. As a second step, the Finite Element Model was used together with Experimental Modal Analyses to identify the vibration modes of the substitute. A shaker excited the structure via a metal rod, while a laser vibrometer recorded the induced vibrations at defined measurement points. The results showed that despite differences in material properties and geometry, the newly developed substitute has 10/13 natural frequencies in common with those of dry human skulls. When filled with a simulant of cerebral matter, it could therefore be used in future studies as an approximation to assess the mechanical response of a simplified skull substitute to a blast threat.
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Surgical corrections of degenerative lumbar scoliosis and sagittal malalignment are associated with significant complications, such as rod fractures and pseudarthrosis, particularly in the lumbosacral junction. Finite element studies can provide relevant insights to improve performance of spinal implants. The aim of the present study was to present the development of non-instrumented and instrumented Finite Element Models (FEMs) of the lumbopelvic spine and to compare numerical results with experimental data available in the literature. The lumbo-pelvic spine FEM was based on a CT-scan from an asymptomatic volunteer representing the 50th percentile male. In a first step a calibration of mechanical properties was performed in order to obtain a quantitative agreement between numerical results and experimental data for defect stages of spinal segments. Then, FEM results were compared in terms of range of motion and strains in rods to in-vitro experimental data from the literature for flexible non-instrumented and instrumented lumbar spines. Numerical results from the calibration process were consistent with experimental data, especially in flexion. A positive agreement was obtained between FEM and experimental results for the lumbar and sacroiliac segments. Instrumented FEMs predicted the same trends as experimental in-vitro studies. The instrumentation configuration consisting of double rods and an interbody cage at L5-S1 maximally reduced range of motion and strains in main rods and thus had the lowest risk of pseudarthrosis and rod fracture. The developed FEMs were found to be consistent with published experimental results; therefore they can be used for further post-operative complication investigations.
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Vértebras Lombares , Fusão Vertebral , Fenômenos Biomecânicos , Análise de Elementos Finitos , Humanos , Vértebras Lombares/diagnóstico por imagem , Vértebras Lombares/cirurgia , Região Lombossacral , Masculino , Amplitude de Movimento ArticularRESUMO
INTRODUCTION: Soccer is the most popular sport in the world. This contact sport carries the risk of exposure to repeated head impacts in the form of subconcussions, defined as minimal brain injuries following head impact, with no symptom of concussion. While it has been suggested that exposure to repetitive subconcussive events can result in long-term neurophysiological modifications, and the later development of chronic traumatic encephalopathy, the consequences of these repeated impacts remain controversial and largely unexplored in the context of soccer players. METHODS AND ANALYSIS: This is a prospective, single-centre, exposure/non-exposure, transverse study assessing the MRI and neuropsychological abnormalities in professional retired soccer players exposed to subconcussive impacts, compared with high-level athletes not exposed to head impacts. The primary outcome corresponds to the results of MRI by advanced MRI techniques (diffusion tensor, cerebral perfusion, functional MRI, cerebral volumetry and cortical thickness, spectroscopy, susceptibility imaging). Secondary outcomes are the results of the neuropsychological tests: number of errors and time to complete tests. We hypothesise that repeated subconcussive impacts could lead to morphological lesions and impact on soccer players' cognitive skills in the long term. ETHICS AND DISSEMINATION: Ethics approval has been obtained and the study was approved by the Comité de Protection des Personnes (CPP) No 2021-A01169-32. Study findings will be disseminated by publication in a high-impact international journal. Results will be presented at national and international imaging meetings. TRIAL REGISTRATION NUMBER: NCT04903015.
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Traumatismos em Atletas , Concussão Encefálica , Futebol , Humanos , Futebol/lesões , Traumatismos em Atletas/diagnóstico por imagem , Traumatismos em Atletas/etiologia , Estudos Prospectivos , Concussão Encefálica/diagnóstico por imagem , Concussão Encefálica/etiologia , CogniçãoRESUMO
Head acceleration measurement sensors are now widely deployed in the field to monitor head kinematic exposure in contact sports. The wealth of impact kinematics data provides valuable, yet challenging, opportunities to study the biomechanical basis of mild traumatic brain injury (mTBI) and subconcussive kinematic exposure. Head impact kinematics are translated into brain mechanical responses through physics-based computational simulations using validated brain models to study the mechanisms of injury. First, this article reviews representative legacy and contemporary brain biomechanical models primarily used for blunt impact simulation. Then, it summarizes perspectives regarding the development and validation of these models, and discusses how simulation results can be interpreted to facilitate injury risk assessment and head acceleration exposure monitoring in the context of contact sports. Recommendations and consensus statements are presented on the use of validated brain models in conjunction with kinematic sensor data to understand the biomechanics of mTBI and subconcussion. Mainly, there is general consensus that validated brain models have strong potential to improve injury prediction and interpretation of subconcussive kinematic exposure over global head kinematics alone. Nevertheless, a major roadblock to this capability is the lack of sufficient data encompassing different sports, sex, age and other factors. The authors recommend further integration of sensor data and simulations with modern data science techniques to generate large datasets of exposures and predicted brain responses along with associated clinical findings. These efforts are anticipated to help better understand the biomechanical basis of mTBI and improve the effectiveness in monitoring kinematic exposure in contact sports for risk and injury mitigation purposes.
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Concussão Encefálica , Esportes , Humanos , Aceleração , Cabeça/fisiologia , Fenômenos Biomecânicos , EncéfaloRESUMO
OBJECTIVE: The automotive industry's shift toward automated vehicles allows the occupants to assume postures different from the standard upright seated position. Injury criteria assessments are needed under these nonstandard postures to advance safety. The objective of this study is to develop a new device that can position the human cadaver head-neck structures in different nonstandard pre-postures using custom devices and apply external loading anticipated in modern and future automotive and military scenarios. METHODS: An isolated head to T1 human cadaver specimen was attached to a load cell at T1. The load cell was fixed to the top of a six-degree-of-freedom custom spinal positioning device to orient the specimen such that the occipital condyle joint was in line with the torque axis of a custom angular displacement test device. The angular device converted the linear motion of a vertically oriented electro-hydraulic piston to a torque about the occipital condyle joint of the specimen. The head was pre-rotated in the axial plane, approximately 20 degrees to the left, while maintaining the coronal alignment of the lower cervical spine. Targets were secured at the head and spine (details in the body of the manuscript), and their three-dimensional positions were measured using a seven-camera optical motion capture system. Right and then left lateral bending tests were conducted. Occipital condyle joint loads were determined from the superior load cell, and the stiffness difference between the left and right lateral bending was determined. RESULTS: The peak coronal bending moments were 27.1 Nm and 47.6 Nm for the right and left lateral bending tests. At the time of the peak x-moment, the y moments were 1.6 and 9.1 Nm, and the z moments were 3.1 and 4.8 Nm. The head angle with respect to T1 at the time of peak x-moments was 28.1 and 27.7 deg about x, 11.0 and 11.7 deg about y, and 33.9 and 21.8 deg about z axes for the right and lateral bending tests. C1 left lateral mass fractured following the left lateral bending test. CONCLUSIONS: The stiffness of the spine increased by approximately three times due to asymmetries in posture and loading. The present system of custom spinal positioning and angular displacement test devices and loading methodologies can be used in conjunction with a conventional piston testing apparatus to conduct additional experiments to delineate the injury patterns and mechanisms and develop injury criteria applicable to modern and future vehicle environments.
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Acidentes de Trânsito , Veículos Autônomos , Fenômenos Biomecânicos , Cadáver , Vértebras Cervicais , Humanos , PosturaRESUMO
Advanced neck finite element modeling and development of neck injury criteria are important for the design of optimal neck protection systems in automotive and other environments. They are also important in virtual tests. The objectives of the present study were to develop a detailed finite element model (FEM) of the human neck and couple it to the existing head model, validate the model with kinematic data from legacy human volunteer and human cadaver impact datasets, and derive lateral impact neck injury risk curves using survival analysis from the upper and lower neck forces and moments. The detailed model represented the anatomy of a young adult mid-size male. It included all the cervical and first thoracic vertebrae, intervening discs, upper and lower spinal ligaments, bilateral facet joints, and passive musculature. Material properties were obtained from literature. Frontal, oblique, and lateral impacts to the distal end of the model was applied based on human volunteer and human cadaver experimental data. Corridor and cross-correlation methods were used for validation. The CORrelation and Analysis (CORA) score was used for objective assessments. Forces and moments were obtained at the occipital condyles (OC) and T1, and parametric survival analysis was used to derive injury risk curves to define human neck injury tolerance to lateral impact. The Brier Score Metric (BSM) was used to determine the hierarchical sequence among the injury metrics. The CORA scores for the lateral, frontal, and oblique impact loading conditions were 0.80, 0.91, and 0.87, respectively, for human volunteer data, and the mean score was 0.7 for human cadaver lateral impacts. Injury risk curves along with ±95% confidence intervals are given for all the four biomechanical metrics. The OC shear force was the optimal metric based on the BSM. A force of 1.5 kN was associated with the 50% probability level of AIS3+ neck injury. As a first step, the presented risk curves serve as human tolerance criteria under lateral impact, hitherto not available in published literatures, and they can be used in virtual testing and advancing restraint systems for improving human safety.
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Acidentes de Trânsito , Pescoço , Fenômenos Biomecânicos , Análise de Elementos Finitos , Cabeça , Humanos , Masculino , Coluna VertebralRESUMO
INTRODUCTION: The evaluation of head protection systems needs proper knowledge of the head impact conditions in terms of impact speed and angle, as well as a realistic estimation of brain tolerance limits. In current bicycle helmet test procedures, both of these aspects should be improved. METHOD: The present paper suggests a bicycle helmet evaluation methodology based on realistic impact conditions and consideration of tissue level brain injury risk, in addition to well known headform kinematic parameters. The method is then applied to a set of 32 existing helmets, leading to a total of 576 experimental impact tests followed by 576 numerical simulations of the brain response. RESULTS: It is shown that the most critical impacts are the linear-lateral ones as well as the oblique impact leading to rotation around the vertical axis (ZRot), leading both to around 50% risks of moderate neurological injuries. Based on this test method, the study enables us to compare the protection capability of a given helmet and eventually to compare helmets via a dedicated rating system.
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Ciclismo , Traumatismos Craniocerebrais/prevenção & controle , Dispositivos de Proteção da Cabeça/estatística & dados numéricos , Segurança/estatística & dados numéricos , Aceleração , Fenômenos Biomecânicos , RotaçãoRESUMO
Experiments have been conducted using isolated tissues of the spine such as ligaments, functional units, and subaxial cervical spine columns. Forces and or moments under external loading can be obtained at the ends of these isolated/segmented preparations; however, these models require fixations at the end(s). To understand the response of the entire cervical spine without the artificial boundary/end conditions, it is necessary to use the whole body human cadaver in the experimental model. This model can be used to obtain the overall kinematics of the head and neck. The forces and moments at each vertebral level of the cervical column segments cannot be directly obtained using the kinematic and mass property data. The objective of this study was to determine such local loads under simulated frontal impact loading using a validated head-neck finite element model and experiments from whole body human cadaver tests, at velocities ranging from 3.9 to 16â¯m/s. The specimens were prepared with a nine linear accelerometer package on the head, and a triaxial accelerometer with a triaxial angular rate sensor on T1, and a set of three non-collinear retroreflective targets were secured to the T1 using the accelerometer mount. A similar array of targets was attached to the skull. Head accelerations were computed at the center of gravity of the head using specimen-specific physical properties. Upper and lower neck forces were computed using center of gravity acceleration data. This dataset was used to verify a previously validated finite element model of the head-neck model by inputting the mean T1 accelerations at different velocities. The model was parametrically exercised from 4 to 16â¯m/s in increments of 3â¯m/s to determine the forces and moments in the local anatomical system at all spinal levels. Results indicated that, with increasing velocities, the axial loading was found to be level-invariant, while the shear force and moment responses depended on the level. The nonuniform developments of the segmental forces and moments across different spinal levels suggest a shift in instantaneous axis of rotations between the across different spinal levels. Such differential changes between contiguous levels may lead to local spinal instability, resulting in long-term effects such as accelerated degeneration and spondylosis. The study underscored the need to conduct additional research to include effects of posture and geometrical variations that exist between males and females for a more comprehensive understanding of the local load-sharing in frontal impacts.
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Cadáver , Vértebras Cervicais , Análise de Elementos Finitos , Teste de Materiais , Fenômenos Mecânicos , Fenômenos Biomecânicos , HumanosRESUMO
Blast pulmonary trauma are common consequences of modern war and terrorism action. To better protect soldiers from that threat, the injury risk level when protected and unprotected must be assessed. Knowing from the literature that a possible amplification of the blast threat would be provided by some thoracic protective systems, the objective is to propose an original approach to correlate a measurable parameter on a manikin with a pulmonary risk level. Using a manikin whose response is correlated with the proposed tolerance limits should help in the evaluation of thoracic protective system regarding injury outcomes. A database including lung injury data from large mammals have been created, allowing the definition of iso-impulse tolerance limits from no lung injury to severe ones (â¼60% of ecchymosis). As the use of this metric is not sufficient to evaluate the performance of protective systems on a manikin, the iso-impulse tolerance limits were associated with the thoracic response of post-mortem swine under blast loading. It was found that the lung injury threshold in terms of incident impulse is 58.3â¯kPa·ms, corresponding to a chest wall peak of acceleration/velocity/displacement of 7350â¯m/s2, 3.7â¯m/s and 6.4â¯mm respectively. Lung injuries are considered as severe (30-60% of ecchymosis) when the incident impulse exceed 232.8â¯kPa·ms, leading to a chest wall peak of acceleration/velocity/displacement of 79.7â¯km/s2, 14.7â¯m/s and 30.1â¯mm respectively. The defined lung tolerance limits are valid for a 50â¯kg swine (unprotected) exposed side-on to the blast threat and against a wall.
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Traumatismos por Explosões/diagnóstico , Explosões , Lesão Pulmonar/diagnóstico , Animais , Traumatismos por Explosões/patologia , Humanos , Medição de Risco , SuínosRESUMO
BACKGROUND: A novel bicycle helmet concept has been developed to mitigate rotational head acceleration, which is a predominant mechanism of traumatic brain injury (TBI). This WAVECEL concept employs a collapsible cellular structure that is recessed within the helmet to provide a rotational suspension. This cellular concept differs from other bicycle helmet technologies for mitigation of rotational head acceleration, such as the commercially available Multi-Directional Impact Protection System (MIPS) technology which employs a slip liner to permit sliding between the helmet and the head during impact. This study quantified the efficacy of both, the WAVECEL cellular concept, and a MIPS helmet, in direct comparison to a traditional bicycle helmet made of rigid expanded polystyrene (EPS). METHODS: Three bicycle helmet types were subjected to oblique impacts in guided vertical drop tests onto an angled anvil: traditional EPS helmets (CONTROL group); helmets with a MIPS slip liner (SLIP group); and helmets with a WAVECEL cellular structure (CELL group). Helmet performance was evaluated using 4.8 m/s impacts onto anvils angled at 30°, 45°, and 60° from the horizontal plane. In addition, helmet performance was tested at a faster speed of 6.2 m/s onto the 45° anvil. Five helmets were tested under each of the four impact conditions for each of the three groups, requiring a total of 60 helmets. Headform kinematics were acquired and used to calculate an injury risk criterion for Abbreviated Injury Score (AIS) 2 brain injury. RESULTS: Linear acceleration of the headform remained below 90 g and was not associated with the risk of skull fracture in any impact scenario and helmet type. Headform rotational acceleration in the CONTROL group was highest for 6.2 m/s impacts onto the 45° anvil (7.2 ± 0.6 krad/s2). In this impact scenario, SLIP helmets and CELL helmets reduced rotational acceleration by 22% (p = 0003) and 73% (p < 0.001), respectively, compared to CONTROL helmets. The CONTROL group had the highest AIS 2 brain injury risk of 59 ± 8% for 6.2 m/s impacts onto the 45° anvil. In this impact scenario, SLIP helmets and CELL helmets reduced the AIS 2 brain injury risk to 34.2% (p = 0.001) and 1.2% (p < 0.001), respectively, compared to CONTROL helmets. DISCUSSION: Results of this study are limited to a narrow range of impact conditions, but demonstrated the potential that rotational acceleration and the associated brain injury risk can be significantly reduced by the cellular WAVECEL concept or a MIPS slip liner. Results obtained under specific impact angles and impact velocities indicated performance differences between these mechanisms. These differences emphasize the need for continued research and development efforts toward helmet technologies that further improve protection from brain injury over a wide range a realistic impact parameters.
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Ciclismo/lesões , Lesões Encefálicas Traumáticas/prevenção & controle , Dispositivos de Proteção da Cabeça , Aceleração/efeitos adversos , Fenômenos Biomecânicos , Estudos de Casos e Controles , Desenho de Equipamento , HumanosRESUMO
The knowledge of in vivo brain tissue mechanical properties is essential in several biomedical engineering fields, such as injury biomechanics and neurosurgery simulation. Almost all existing available data have been obtained in vitro by invasive experimental protocols. However, the difference between in vivo and post-mortem mechanical properties remains poorly known, essentially due to the lack of a common method that could measure them both in vivo and ex vivo. In this study, we report the use of magnetic resonance elastography (MRE) for the non-invasive assessment of in vivo brain tissue viscoelastic properties and for the investigation of their evolution after the death. Experiments were performed on seven adult male rats. Shear storage and loss moduli were measured in vivo, just after death and at post-mortem time of approximately 24h. A significant increase in shear storage modulus G(') of approximately 100% was found to occur just after death (p=0.002), whereas no significant difference was found between in vivoG(') and G(') at 24h post-mortem time. No significant difference was found between shear loss modulus G('')in vivo and just after death, whereas a decrease of about 50% was found to occur after 24h (p=0.02). These results illustrate the ability of MRE to investigate some of the critical soft tissue biomechanics-related issues, as it can be used as a non-invasive tool for measuring soft tissue viscoelastic properties.
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Encéfalo/patologia , Encéfalo/fisiopatologia , Técnicas de Imagem por Elasticidade/métodos , Interpretação de Imagem Assistida por Computador/métodos , Imageamento por Ressonância Magnética/métodos , Modelos Biológicos , Mudanças Depois da Morte , Animais , Simulação por Computador , Módulo de Elasticidade , Masculino , Ratos , Ratos Sprague-Dawley , Estresse Mecânico , ViscosidadeRESUMO
The objective of the present study is to synthesize and investigate using the same set of sixty-one real-world accidents the human head injury prediction capability of the head injury criterion (HIC) and the head impact power (HIP) based criterion as well as the injury mechanisms related criteria provided by the simulated injury monitor (SIMon) and the Louis Pasteur University (ULP) finite element head models. Each accident has been classified according to whether neurological injuries, subdural haematoma and skull fractures were reported. Furthermore, the accidents were reconstructed experimentally or numerically in order to provide loading conditions such as acceleration fields of the head or initial head impact conditions. Finally, thanks to this large statistical population of head trauma cases, injury risk curves were computed and the corresponding regression quality estimators permitted to check the correlation of the injury criteria with the injury occurrences. As different kinds of accidents were used, i.e. footballer, motorcyclist and pedestrian cases, the case-independency could also be checked. As a result, FE head modeling provides essential information on the intracranial mechanical behavior and, therefore, better injury criteria can be computed. It is clearly shown that moderate and severe neurological injuries can only be distinguished with a criterion that is computed using intracranial variables and not with the sole global head acceleration.
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Acidentes de Trânsito/estatística & dados numéricos , Traumatismos Craniocerebrais/epidemiologia , Futebol/lesões , Adulto , Fenômenos Biomecânicos , Traumatismos Craniocerebrais/etiologia , Escala de Coma de Glasgow , Indicadores Básicos de Saúde , Humanos , Escala de Gravidade do Ferimento , Modelos Logísticos , Masculino , Modelos Estatísticos , Medição de Risco , Fatores de Risco , Índices de Gravidade do TraumaRESUMO
Biomechanics of human head has been widely studied since several decades. At a mechanical level, the use of engineering allowed investigating injury mechanisms developing numerical models of adult head. For children, the problem is more difficult and evaluating child injury mechanisms using data obtained from scaling adult injury criteria does not account for differences in morphology and structure between adults and children. During growth, child head undergoes different modifications in morphology and structure. The present paper compares the anthropometry and numerical simulations of a child head model based on medical CT scans to a child head model developed by scaling an adult head model using the method proposed by Mertz [H.J. Mertz, A procedure for normalizing impact response data, SAE paper 840884, 1984]. These analysis point out significant differences showing that scaling down an adult head to obtain a child head does not appear relevant. Biofidelic and specific child geometry is needed to investigate child injury mechanisms.
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Simulação por Computador , Traumatismos Craniocerebrais/etiologia , Análise de Elementos Finitos , Cabeça/anatomia & histologia , Modelos Anatômicos , Adolescente , Adulto , Fenômenos Biomecânicos , Encéfalo/anatomia & histologia , Encéfalo/crescimento & desenvolvimento , Criança , Pré-Escolar , Traumatismos Craniocerebrais/patologia , Traumatismos Craniocerebrais/fisiopatologia , Cabeça/crescimento & desenvolvimento , Humanos , Lactente , Recém-NascidoRESUMO
Retinal hemorrhages (RH) are among injuries sustained by a large number of shaken baby syndrome victims, but also by a small proportion of road accident victims. In order to have a better understanding of the underlying of RH mechanisms, we aimed to develop a complete human eye and orbit finite element model. Five occipital head impacts, at different heights and on different surfaces, and three shaking experiments were conducted with a 6-week-old dummy (Q0 dummy). This allowed obtaining a precise description of the motion in those two specific situations, which was then used as input for the eye model simulation. Results showed that four parameters (pressure, Von Mises stress and strain, 1st principal stress) are relevant for shaking-fall comparison. Indeed, in the retina, the softest shaking leads to pressure that is 4 times higher than the most severe impact (1.43 vs. 0.34 kPa). For the Von Mises stress, strain and 1st principal stress, this ratio rises to 4.27, 6.53 and 14.74, respectively. Moreover, regions of high stress and strain in the retina and the choroid were identified and compared to what is seen on fundoscopy. The comparison between linear and rotational acceleration in fall and shaking events demonstrated the important role of the rotational acceleration in inducing such injuries. Even though the eye model was not validated, the conclusion of this study is that compared to falls, shaking an infant leads to extreme eye loading as demonstrated by the values taken by the four mentioned mechanical parameters in the retina and the choroid.
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Olho/patologia , Análise de Elementos Finitos , Modelos Biológicos , Hemorragia Retiniana/patologia , Síndrome do Bebê Sacudido/patologia , Aceleração , Corioide/patologia , Simulação por Computador , Humanos , Lactente , Pressão , Estresse Mecânico , Fatores de TempoRESUMO
To better protect soldiers from blast threat, that principally affect air-filled organs such a lung, it is necessary to develop an adapted injury criterion and, prior to this, to evaluate the response of a biological model against that threat. The objective of this study is to provide some robust data to quantify the chest response of post-mortem swine under blast loadings. 7 post-mortem swine (54.5⯱â¯2.6â¯kg), placed side-on to the threat and against the ground, were exposed to 5 shock-waves of increasing intensities. Their thorax were instrumented with a piezo-resistive pressure sensor, an accelerometer directly exposed to the shock-wave and a target was mounted on the latter in order to track the chest wall displacement. For incident impulses ranging from 47â¯kPaâ¯ms±2% to 173â¯kPaâ¯ms⯱6%, the measured maximum of linear chest wall acceleration (Γmax) goes from 5800â¯m/s2⯱16% to 41,000â¯m/s2⯱â¯8%, with a duration of 0.8â¯ms. Chest wall displacements ranging from 5â¯mm⯱â¯20% to 20â¯mm⯱â¯15%, with a duration of 9â¯ms, are reached. These reproducible data were used to find simple relations (linear, 2nd and 3rd order polynomials) between the kinematic parameters (plus the viscous criterion) and the incident and reflected impulses. Correlating the new reproducible data with the prediction from the Bowen curves showed a lung injury threshold in terms of Γmax similar to that of Cooper (10,000â¯m/s2). However, the limits defined for the viscous criterion in the automobile field and for non-lethal weapons seems not adapted for the blast threat.
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Traumatismos por Explosões/prevenção & controle , Explosões , Lesão Pulmonar/prevenção & controle , Animais , Traumatismos por Explosões/patologia , Feminino , Humanos , Pulmão/patologia , Lesão Pulmonar/patologia , Masculino , Modelos Biológicos , Sus scrofa , Tórax/patologiaRESUMO
Traumatic brain injury (TBI) is the leading cause of death and permanent impairment over the last decades. In both the severe and mild TBIs, diffuse axonal injury (DAI) is the most common pathology and leads to axonal degeneration. Computation of axonal strain by using finite element head model in numerical simulation can enlighten the DAI mechanism and help to establish advanced head injury criteria. The main objective of this study is to develop a brain injury criterion based on computation of axonal strain. To achieve the objective a state-of-the-art finite element head model with enhanced brain and skull material laws, was used for numerical computation of real world head trauma. The implementation of new medical imaging data such as, fractional anisotropy and axonal fiber orientation from Diffusion Tensor Imaging (DTI) of 12 healthy patients into the finite element brain model was performed to improve the brain constitutive material law with more efficient heterogeneous anisotropic visco hyper-elastic material law. The brain behavior has been validated in terms of brain deformation against Hardy et al. (2001), Hardy et al. (2007), and in terms of brain pressure against Nahum et al. (1977) and Trosseille et al. (1992) experiments. Verification of model stability has been conducted as well. Further, 109 well-documented TBI cases were simulated and axonal strain computed to derive brain injury tolerance curve. Based on an in-depth statistical analysis of different intra-cerebral parameters (brain axonal strain rate, axonal strain, first principal strain, Von Mises strain, first principal stress, Von Mises stress, CSDM (0.10), CSDM (0.15) and CSDM (0.25)), it was shown that axonal strain was the most appropriate candidate parameter to predict DAI. The proposed brain injury tolerance limit for a 50% risk of DAI has been established at 14.65% of axonal strain. This study provides a key step for a realistic novel injury metric for DAI.
Assuntos
Encéfalo/fisiologia , Líquido Cefalorraquidiano/fisiologia , Lesão Axonal Difusa , Crânio/fisiologia , Estresse Mecânico , Axônios , Lesões Encefálicas , Traumatismos Craniocerebrais , Imagem de Tensor de Difusão , Análise de Elementos Finitos , Cabeça , Humanos , Modelos Logísticos , Modelos Teóricos , PressãoRESUMO
The objective of this study was to enhance an existing finite element (FE) head model with composite modeling and a new constitutive law for the skull. The response of the state-of-the-art FE head model was validated in the time domain using data from 15 temporo-parietal impact experiments, conducted with postmortem human surrogates. The new model predicted skull fractures observed in these tests. Further, 70 well-documented head trauma cases were reconstructed. The 15 experiments and 70 real-world head trauma cases were combined to derive skull fracture injury risk curves. The skull internal energy was found to be the best candidate to predict skull failure based on an in depth statistical analysis of different mechanical parameters (force, skull internal energy), head kinematic-based parameter, the head injury criterion (HIC), and skull fracture correlate (SFC). The proposed tolerance limit for 50% risk of skull fracture was associated with 453mJ of internal energy. Statistical analyses were extended for individual impact locations (frontal, occipital and temporo-parietal) and separate injury risk curves were obtained. The 50% risk of skull fracture for each location: frontal: 481mJ, occipital: 457mJ, temporo-parietal: 456mJ of skull internal energy.
Assuntos
Análise de Elementos Finitos , Cabeça , Fenômenos Mecânicos , Fraturas Cranianas , Fenômenos Biomecânicos , Humanos , ProbabilidadeRESUMO
Since World War II, researchers have been interested in exploring the injury mechanisms involved in primary blast on the thorax by using animal model surrogates. These studies were mostly concerned with the finding of the lung injury threshold, the relationship between the physical components of the air blast wave, and the biological response. Studies have also been conducted to investigate the effect of repeated blast exposures on the injury outcome threshold. This has led to several injury criteria, such as the Bowen curves based on pressure history's characteristics or the Axelsson Chest Wall Velocity Predictor that used measurement from the mammals' chest wall. This article aims at doing a critical literature review of this specific topic.