Effects of fall conditions and biological variability on the mechanism of skull fractures caused by falls

Depressed fractures of the skull due to direct kick and the contribution of 3D CT reconstruction

Depressed skull fractures occur when broken bones displace inward, meaning that a portion of the outer table of the fracture line lies below the normal anatomical position of the inner table. They typically result from force trauma, when the skull is struck by an object with a moderately large amount of kinetic energy but a small surface area, or when an object with a large amount of kinetic energy impacts only a small area of the skull. In the present case, a depressed fracture of the frontal bone was detected at the autopsy of a 52-year-old man who, according to the belated confession of the assailant, was kicked in the head. The assailant was wearing sneakers. Could such a fracture be caused "just" by a kick? In this case it was possible due to an extraordinarily thin cranial vault (0.2 cm frontal, 0.3 cm occipital), which allowed the fractures to occur from a kinetic force that might not have been sufficient with a normal cranial vault thickness. An important role in the forensic analysis of the case was played by the 3D CT reconstruction.

Subject-specific finite element head models for skull fracture evaluation-a new tool in forensic pathology

Post-mortem computed tomography (PMCT) enables the creation of subject-specific 3D head models suitable for quantitative analysis such as finite element analysis (FEA). FEA of proposed traumatic events is an objective and repeatable numerical method for assessing whether an event could cause a skull fracture such as seen at autopsy. FEA of blunt force skull fracture in adults with subject-specific 3D models in forensic pathology remains uninvestigated. This study aimed to assess the feasibility of FEA for skull fracture analysis in routine forensic pathology. Five cases with blunt force skull fracture and sufficient information on the kinematics of the traumatic event to enable numerical reconstruction were chosen. Subject-specific finite element (FE) head models were constructed by mesh morphing based on PMCT 3D models and A Detailed and Personalizable Head Model with Axons for Injury Prediction (ADAPT) FE model. Morphing was successful in maintaining subject-specific 3D geometry and quality of the FE mesh in all cases. In three cases, the simulated fracture patterns were comparable in location and pattern to the fractures seen at autopsy/PMCT. In one case, the simulated fracture was in the parietal bone whereas the fracture seen at autopsy/PMCT was in the occipital bone. In another case, the simulated fracture was a spider-web fracture in the frontal bone, whereas a much smaller fracture was seen at autopsy/PMCT; however, the fracture in the early time steps of the simulation was comparable to autopsy/PMCT. FEA might be feasible in forensic pathology in cases with a single blunt force impact and well-described event circumstances.

Head injury: Importance of the deep brain nuclei in force transmission to the brain

Finite element modeling provides a digital representation of the human body. It is currently the most pertinent method to study the mechanisms of head injury, and is becoming a scientific reference in forensic expert reports. Improved biofidelity is a recurrent aim of research studies in biomechanics in order to improve earlier models whose mechanical properties conformed to simplified elastic behavior and mechanic laws. We aimed to study force transmission to the brain following impacts to the head, using a finite element head model with increased biofidelity. To the model developed by the Laboratory of Applied Biomechanics of Marseille, we added new brain structures (thalamus, central gray nuclei and ventricular systems) as well as three tracts involved in the symptoms of head injury: the corpus callosum, uncinate tracts and corticospinal tracts. Three head impact scenarios were simulated: an uppercut with the prior model and an uppercut with the improved model in order to compare the two models, and a lateral impact with an impact velocity of 6.5 m/s in the improved model. In these conditions, in uppercuts the maximum stress values did not exceed the injury risk threshold. On the other hand, the deep gray matter (thalamus and central gray nuclei) was the region at highest risk of injury during lateral impacts. Even if injury to the deep gray matter is not immediately life-threatening, it could explain the chronic disabling symptoms of even low-intensity head injury.

Prediction of skull fractures in blunt force head traumas using finite element head models

Traumatic head injuries remain a leading cause of death and disability worldwide. Although skull fractures are one of the most common head injuries, the fundamental mechanics of cranial bone and its impact tolerance are still uncertain. In the present study, a strain-rate-dependent material model for cranial bone has been proposed and implemented in subject-specific Finite Element (FE) head models in order to predict skull fractures in five real-world fall accidents. The subject-specific head models were developed following an established image-registration-based personalization pipeline. Head impact boundary conditions were derived from accident reconstructions using personalized human body models. The simulated fracture lines were compared to those visible in post-mortem CT scans of each subject. In result, the FE models did predict the actual occurrence and extent of skull fractures in all cases. In at least four out of five cases, predicted fracture patterns were comparable to ones from CT scans and autopsy reports. The tensile material model, which was tuned to represent rate-dependent tensile data of cortical skull bone from literature, was able to capture observed linear fractures in blunt indentation loading of a skullcap specimen. The FE model showed to be sensitive to modeling parameters, in particular to the constitutive parameters of the cortical tables. Nevertheless, this study provides a currently lacking strain-rate dependent material model of cranial bone that has the capacity to accurately predict linear fracture patterns. For the first time, a procedure to reconstruct occurrences of skull fractures using computational engineering techniques, capturing the all-in-all fracture initiation, propagation and final pattern, is presented.

Thoughts and perspectives on biomechanical numerical models under impacts: Are women forgotten from research?

The present paper explores a series of articles in the literature which deal with impact biomechanics of the head and thorax/abdomen segments, investigating the "sex specific properties/data" used in the studies. Statements in these studies are analyzed and point out, the use of male or female subjects for the developments of finite element models and their validation against experimental data. The present analysis raises the question about "androcentrism," and how biomechanical engineering findings and the design of the derived protecting devices are focused on male subjects.

Injuries in Underbody Blast Fatalities: Identification of Five Distinct Mechanisms of Head Injury

Previous research has shown that injuries to the head and neck were prevalent in 73% of all mounted fatalities of underbody blast. The mechanisms that cause such injuries to the central nervous system (CNS) are not yet known. The aim of this study was to identify the head and spinal injuries in fatalities due to underbody blast (UBB) and then develop hypotheses on the causative mechanisms. All U.K. military fatalities from UBB with an associated head injury that occurred during 2007-2013 in the Iraq and Afghanistan conflicts were identified retrospectively. Computed tomography post-mortems (CTPMs) were interrogated for injuries to the head, neck, and spine. All injuries were documented and classified using a radiology classification. Pearson's chi-square and Fisher's exact tests were used to show a relationship between variables and form a hypothesis for injury mechanisms. There were 50 fatalities from UBB with an associated head injury. Of these, 46 had complete CTPMs available for analysis. Chi-square and Fisher's exact tests showed a relationship between lateral ventricle blood and injuries to the abdomen and thorax. Five partially overlapping injury constellations were identified: 1.multiple-level spinal injury with skull fracture and brainstem injury, 2.peri-mesencephalic hemorrhage, 3.spinal and brainstem injury, 4.parenchymal contusions with injury to C0-C1, and 5.an "eggshell" pattern of fractures from direct impact. These injury constellations can now be used to propose injury mechanisms to develop mitigation strategies or clinical treatments.

The issues and complexities of establishing methodologies to differentiate between vertical and horizontal impact mechanisms in the analysis of skeletal trauma: An introductory femoral test

Understanding skeletal trauma characteristics is fundamental for the examination and interpretation of blunt force trauma (BFT). BFT is the most complex type of trauma to interpret based on the analysis of skeletal fractures alone, with comminuted fractures presenting additional complications to assess and interpret. Considerable variation exists within each type of BFT injury dependent on direction, magnitude of force, plus a myriad of biological/environmental factors. Given the complex processes governing the nature of BFT skeletal injuries determining whether differences between impact mechanisms and skeletal trauma can be quantified requires investigation.

AIM

this study aims to determine the feasibility of quantifying outcomes between two separate loading conditions by using a formula created from transformed variables recorded from specific trauma cases involving BFT to the femur.

METHODOLOGY

Displacement, comminution, and femoral midshaft area data were recorded from full body postmortem computed tomography scans of 103 individuals (males, mean age 42.5, and females, mean age 48.9) where cause of death was the result of rapid horizontal deceleration impact events (pedestrian motor vehicular accidents, n = 59) and vertical (>3-metre falls, n = 44). These measurements were standardised and transformed into a continuous variable. Independent t-tests, binary logistic regression and K Nearest- Neighbours (KNN) were used to analyse the data.

RESULTS

The standardised values showed mean group differences between falls (9.62) and pedestrian motor vehicular impacts (pedestrian MVAs) (9.53), however, these results were not statistically significant. The results indicate that similarities in variance between types of trauma outcomes and impact mechanisms demonstrate low equivalency (samples have limited differences), and the overall limitations in relying on using single elements to explain complex skeletal trauma outcomes.

Skull Fractures Induce Neuroinflammation and Worsen Outcomes after Closed Head Injury in Mice

The weight-drop model is used widely to replicate closed-head injuries in mice; however, the histopathological and functional outcomes may vary significantly between laboratories. Because skull fractures are reported to occur in this model, we aimed to evaluate whether these breaks may influence the variability of the weight-drop (WD) model. Male Swiss Webster mice underwent WD injury with either a 2 or 5 mm cone tip, and behavior was assessed at 2 h and 24 h thereafter using the neurological severity score. The expression of interleukin (IL)-6, IL-1β, tumor necrosis factor-α, matrix metalloproteinase-9, and tissue inhibitor of metalloproteinase-1 genes was measured at 12 h and 1, 3, and 14 days after injury. Before the injury, micro-computed tomography (micro-CT) was performed to quantify skull thickness at the impact site. With a conventional tip diameter of 2 mm, 33% of mice showed fractures of the parietal bone; the 5 mm tip produced only 10% fractures. Compared with mice without fractures, mice with fractures had a severity-dependent worse functional outcome and a more pronounced upregulation of inflammatory genes in the brain. Older mice were associated with thicker parietal bones and were less prone to skull fractures. In addition, mice that underwent traumatic brain injury (TBI) with skull fracture had macroscopic brain damage because of skull depression. Skull fractures explain a considerable proportion of the variability observed in the WD model in mice—i.e., mice with skull fractures have a much stronger inflammatory response than do mice without fractures. Using older mice with thicker skull bones and an impact cone with a larger diameter reduces the rate of skull fractures and the variability in this very useful closed-head TBI model.

Risk of frontal sinus anterior table fractures after craniofacial trauma and the role of anatomic variations in frontal sinus size: A retrospective case-control study

INTRODUCTION

Purpose of this study was to evaluate a probable risk of frontal sinus size for traumatic depressed anterior table fractures in patients with similar forehead trauma.

METHODS

We conducted a retrospective case-control study with a case group of consecutive treated patients with displaced frontal sinus anterior table fractures. The control group was randomly sampled from patients who presented with a blunt forehead trauma in our institution's emergency unit. In computed tomography data sets, all patients' frontal sinus size was categorized by Guerram's classification that is defined as aplasia, hypoplasia, medium-size and hyperplasia. Odds for prevalence of the sinus types as well as sinus total width and height were compared between both groups.

RESULTS

In total, 47 cases and 93 controls were identified. Hyperplasia in the case group had an odds ratio of 46:1 (p < 0.001) compared to the controls. Mean sinus width (73 mm vs. 46 mm; p < 0.001) and sinus height (30 mm vs. 15 mm; p < 0.001) were larger in the case group.

CONCLUSION

Depressed traumatic fractures of the anterior table are an injury with a high risk specific for enlarged frontal sinus sizes. Anatomy is the predictive factor for this mode of craniofacial trauma.

Death due to fracture of thin calvarial bones after a fall: A forensic approach

A 45-year-old male was autopsied. He had fallen backwards from a two-stairs height to the ground and passed away. A skull fracture was detected in the left occipital area, extending up to the left side of the skull base. The patient's death occurred due to the very low thickness of the calvarial bones, which led to the aforementioned fracture, and in turn resulted in subarachnoid hemorrhage and death. The cortical thickness was measured and compared with average values at standardized points. Uniform bone thinning was confirmed rather than localized. Calvarial thinning may result from various conditions. In the present case study, however, the exact mechanism which led to the low thickness of the calvarial bones of the patient is undetermined. Death due to the susceptible structure and fracture of calvarial bones has rarely been reported throughout relevant literature.

The importance of nonlinear tissue modelling in finite element simulations of infant head impacts

Despite recent efforts on the development of finite element (FE) head models of infants, a model capable of capturing head responses under various impact scenarios has not been reported. This is hypothesized partially attributed to the use of simplified linear elastic models for soft tissues of suture, scalp and dura. Orthotropic elastic constants are yet to be determined to incorporate the direction-specific material properties of infant cranial bone due to grain fibres radiating from the ossification centres. We report here on our efforts in advancing the above-mentioned aspects in material modelling in infant head and further incorporate them into subject-specific FE head models of a newborn, 5- and 9-month-old infant. Each model is subjected to five impact tests (forehead, occiput, vertex, right and left parietal impacts) and two compression tests. The predicted global head impact responses of the acceleration-time impact curves and the force-deflection compression curves for different age groups agree well with the experimental data reported in the literature. In particular, the newly developed Ogden hyperelastic model for suture, together with the nonlinear modelling of scalp and dura mater, enables the models to achieve more realistic impact performance compared with linear elastic models. The proposed approach for obtaining age-dependent skull bone orthotropic material constants counts both an increase in stiffness and decrease in anisotropy in the skull bone-two essential biological growth parameters during early infancy. The profound deformation of infant head causes a large stretch at the interfaces between the skull bones and the suture, suggesting that infant skull fractures are likely to initiate from the interfaces; the impact angle has a profound influence on global head impact responses and the skull injury metrics for certain impact locations, especially true for a parietal impact.

Fatal traumatic brain injury with electrical weapon falls

INTRODUCTION

While generally reducing morbidity and mortality, electrical weapons have risks associated with their usage, including eye injuries and falls. With sufficient probe spread, an uncontrolled fall to the ground typically occurs along with the possibility of a fatal brain injury.

METHODS

We analyzed possible risk factors including running and elevated surfaces with established head-injury criteria to estimate the risk of brain injury. We searched for cases of arrest-related or in-custody death, with TASER(®) electrical weapon usage where fall-induced injuries might have contributed to the death. We found 24 cases meeting our initial inclusion criteria of a fatal fall involving electronic control. We then excluded 5 cases as intentional jumps, leaving 19 cases of forced falls. Autopsy reports and other records were analyzed to determine which of these deaths were from brain injury caused by the fall.

RESULTS

We found 16 probable cases of fatal brain injuries induced by electronic control from electrical weapons. Out of 3 million field uses, this gives a risk of 5.3 ± 2.6 PPM which is higher than the theoretical risk of electrocution. The mean age was 46 ± 14 years which is significantly greater that the age of the typical ARD (36 ± 10). Probe shots to the subject's back may present a higher risk of a fatal fall.

CONCLUSIONS

The use of electronic control presents a small but real risk of death from fatal traumatic brain injury. Increased age represents an independent risk factor for such fatalities.

Fall from a car driving at high speed: A case report

In cases of falls, the key issue for forensic scientists is to determine the manner of death. They must distinguish between accidental falls, suicidal falls, falls including blows and falls caused by a blow. Several strategies have been proposed in the literature to help explain injury patterns. Here, we report an original case of a man who died after jumping from a car moving at high speed. A mathematical and modeling approach was developed to reconstruct the trajectory of the body in order to understand the injury pattern and apparent discrepancy between the high speed of the car from which the victim jumped and the topography of the bone fractures, which were limited to the skull. To define the initial values of the model's parameters, a technical vehicle evaluation and several test jumps at low speed were carried out. We studied in greater detail the trajectory of three characteristic points corresponding to the dummy's center of gravity, head and right foot. Calculations were made with and without the air friction effect to show its influence. Finally, we were successful in modeling the initial trajectory of the body and the variation of its head energy over time, which were consistent with the injuries observed.

Analysis of Closed Soft Tissue Subcutaneous Injuries-"Impact Décollement" in Fatal Free Falls From Height-Forensic Aspect

The aim of this study was to assess the frequency of "décollement," traumatic lesions of subcutaneous soft tissue, among victims fatally injured because of falls from different heights. Three hundred seventy-five cases of fatalities due to injuries acquired when falling from various heights onto a solid, flat surface, in which the complete forensic autopsy was performed, were analyzed. Décollement was noted in 125 (33%) of the cases. Comparative analysis of groups with and without décollement and observed factors has shown that the height of fall and the manner of death have statistically significant influence on décollement appearance. With regard to suicidal, accidental, or undefined origin of death décollement is statistically more common in accidental deaths. Décollement provides important clues for forensic reconstruction and could be a significant indicator of the body's position at primary impact and the height from which the victim has either jumped or fallen.

Maxillofacial fractures and craniocerebral injuries - stress propagation from face to neurocranium in a finite element analysis

Background

Severe facial trauma is often associated with intracerebral injuries. So it seemed to be of interest to study stress propagation from face to neurocranium after a fistlike impact on the facial skull in a finite element analysis.

Methods

A finite element model of the human skull without mandible consisting of nearly 740,000 tetrahedrons was built. Fistlike impacts on the infraorbital rim, the nasoorbitoethmoid region, and the supraorbital arch were simulated and stress propagations were depicted in a time-dependent display.

Results

Finite element simulation revealed von Mises stresses beyond the yield criterion of facial bone at the site of impacts and propagation of stresses in considerable amount towards skull base in the scenario of the fistlike impact on the infraorbital rim and on the nasoorbitoethmoid region. When impact was given on the supraorbital arch stresses seemed to be absorbed.

Conclusions

As patients presenting with facial fractures have a risk for craniocerebral injuries attention should be paid to this and the indication for a CT-scan should be put widely. Efforts have to be made to generate more precise finite element models for a better comprehension of craniofacial and brain injury.

Electronic supplementary material

The online version of this article (doi:10.1186/s13049-015-0117-z) contains supplementary material, which is available to authorized users.

Comparative analysis between identified injuries of victims of fall from height and other mechanisms of closed trauma

OBJECTIVE: To analyze the lesions diagnosed in victims of falls, comparing them with those diagnosed in other mechanisms of blunt trauma.METHODS: We conducted a retrospective study of trauma protocol charts (prospectively collected) from 2008 to 2010, including victims of trauma over 13 years of age admitted to the emergency room. The severity of injuries was stratified by the Abbreviated Injury Scale (AIS) and Injury Severity Score (ISS). Variables were compared between the group of victims of falls from height (Group 1) and the other victims of blunt trauma (Group 2). We used the Student t, chi-square and Fisher tests for comparison between groups, considering the value of p <0.05 as significant.RESULTS: The series comprised 4,532 cases of blunt trauma, of which 555 (12.2%) were victims of falls from height. Severe lesions (AISe"3) were observed in the extremities (17.5%), in the cephalic segment (8.4%), chest (5.5%) and the abdomen (2.9%). Victims of Group 1 had significantly higher mean age, AIS in extremities / pelvis, AIS in the thoracic segment and ISS (p <0.05). The group 1 had significantly (p <0.05) higher incidence of tracheal intubation on admission, pneumothorax, hemothorax, rib fractures, chest drainage, spinal trauma, pelvic fractures, complex pelvic fractures and fractures to the upper limbs.CONCLUSION: Victims of fall from height had greater anatomic injury severity, greater frequency and severity of lesions in the thoracic segment and extremities.

Applicability of cranial models in urethane resin and foam as a substitute for bone: are synthetic materials reliable?

As literature is poor in functional synthetic cranial models, in this study, synthetic handmade models of cranial vaults were produced in two different materials (a urethane resin and a self-hardening foam), from multiple bone specimens (eight original cranial vaults: four human and four swine), in order to test their resemblance to bone structure in behavior, during fracture formation. All the vaults were mechanically tested with a 2-kg impact weight and filmed with a high-speed camera. Fracture patterns were homogeneous in all swine vaults and heterogeneous in human vaults, with resin fractures more similar to bone fractures. Mean fracture latency time extrapolated by videos were of 0.75 msec (bone), 1.5 msec (resin), 5.12 msec (foam) for human vaults and of 0.625 msec (bone), 1.87 msec (resin), 3.75 msec (foam) for swine vaults. These data showed that resin models are more similar to bone than foam reproductions, but that synthetic material may behave quite differently from bone as concerns fracture latency times.