Ballistic Impact to the Forehead, Zygoma, and Mandible: Comparison of Human and Frangible Dummy Face Biomechanics

Skin simulants for wound ballistic investigation - an experimental study

Gunshot wound analysis is an important part of medicolegal practice, in both autopsies and examinations of living persons. Well-established and studied simulants exist that exhibit both physical and biomechanical properties of soft-tissues and bones. Current research literature on ballistic wounds focuses on the biomechanical properties of skin simulants. In our extensive experimental study, we tested numerous synthetic and natural materials, regarding their macromorphological bullet impact characteristics, and compared these data with those from real bullet injuries gathered from medicolegal practice. Over thirty varieties of potential skin simulants were shot perpendicularly, and at 45°, at a distance of 10 m and 0.3 m, using full metal jacket (FMJ) projectiles (9 × 19 mm Luger). Simulants included ballistic gelatine at various concentrations, dental silicones with several degrees of hardness, alginates, latex, chamois leather, suture trainers for medical training purposes and various material compound models. In addition to complying to the general requirements for a synthetic simulant, results obtained from dental silicones shore hardness 70 (backed with 20 % by mass gelatine), were especially highly comparable to gunshot entry wounds in skin from real cases. Based on these results, particularly focusing on the macroscopically detectable criteria, we can strongly recommend dental silicone shore hardness 70 as a skin simulant for wound ballistics examinations.

Development and validation of a digital twin of the human lower jaw under impact loading by using non-linear finite element analyses

Mandibular fractures are one of the most frequently observed injuries within craniofacial region mostly due to tumor-related problems and traumatic events, often related to non-linear effects like impact loading. Therefore, a validated digital twin of the mandible is required to develop the best possible patient-specific treatment. However, there is a need to obtain a fully compatible numerical model that can reflect the patients' characteristics, be available and accessible quickly, require an acceptable level of modeling efforts and knowledge to provide accurate, robust and fast results at the same time under highly non-linear effects. In this study, a validated simulation methodology is suggested to develop a digital twin of mandible, capable of predicting the non-linear response of the biomechanical system under impact loading, which then can be utilized to design treatment strategies even for multiple fractures of the mandibular system. Using Computed Tomography data containing cranial (skull) images of a patient, a 3-dimensional mandibular model, which consists cortical and cancellous bones, disks and fossa is obtained with high accuracy that is compatible with anatomical boundaries. A Finite Element Model (FEM) of the biomechanical system is then developed for a three-level validation procedure including (A) modal analysis, (B) dynamic loading and (C) impact loading. For the modal analysis stage: Free-free vibration modes and frequencies of the system are validated against cadaver test results. For the dynamic loading stage: Two different regions of the mandible are loaded, and maximum stress levels of the system are validated against finite element analyses (FEA) results, where the first loading condition (i) transfers a 2000 N force acting on the symphysis region and, the second loading condition (ii) transfers a 2000 N force acting on the left body region. In both cases, equivalent muscle forces dependent on time are applied. For the impact loading stage: Thirteen different human mandibular models with various tooth deficiencies are used under the effects of traumatic impact forces that are generated by using an impact hammer with different initial velocities to transfer the impulse and momentum, where contact forces and fracture patterns are validated against cadaver tests. Five different anatomical regions are selected as the impact site. The results of the analyzes (modal, dynamic and impact) performed to validate the digital twin model are compared with the similar FEA and cadaver test results published in the literature and the results are found to be compatible. It has been evaluated that the digital twin model and numerical models are quite realistic and perform well in terms of predicting the biomechanical behavior of the mandible. The three-level validation methodology that is suggested in this research by utilizing non-linear FEA has provided a reliable road map to develop a digital twin of a biomechanical system with enough confidence that it can be utilized for similar structures to offer patient-specific treatments and can help develop custom or tailor-made implants or prosthesis for best compliance with the patient even considering the most catastrophic effects of impact related trauma.

Facial Fracture Injury Criteria from Night Vision Goggle Impact

INTRODUCTION: Military personnel extensively use night vision goggles (NVGs) in contemporary scenarios. Since NVGs may induce or increase injuries from falls or vehicular accidents, biomechanical risk assessments would aid design goal or mitigation strategy development.METHODS: This study assesses injury risks from NVG impact on cadaver heads using impactors modeled on the PVS-14 NVG. Impacts to the zygoma and maxilla were performed at 20° or 40° angles. Risks of facial fracture, neurotrauma, and neck injury were assessed. Acoustic sensors and accelerometers assessed time of fracture and provided input variables for injury risk functions. Injuries were assessed using the Abbreviated Injury Scale (AIS); injury severity was assessed using the Rhee and Donat scales. Risk functions were developed for the input variables using censored survival analyses.RESULTS: The effects of impact angle and bone geometry on injury characteristics were determined with loading area, axial force, energy attenuation, and stress at fracture. Probabilities of facial fracture were quantified through survival analysis and injury risk functions. These risk functions determined a 50% risk of facial bone fracture at 1148 N (axial force) at a 20° maxillary impact, 588 N at a 40° maxillary impact, and 677 N at a 20° zygomatic impact. A cumulative distribution function indicates 769 N corresponds to 50% risk of fracture overall.DISCUSSION: Results found smaller impact areas on the maxilla are correlated with higher angles of impact increasing risk of facial fracture, neck injuries are unlikely to occur before fracture or neurotrauma, and a potential trade-off mechanism between fracture and brain injury.Davis MB, Pang DY, Herring IP, Bass CR. Facial fracture injury criteria from night vision goggle impact. Aerosp Med Hum Perform. 2023; 94(11):827-834.

Review of Mechanisms and Research Methods for Blunt Ballistic Head Injury

Head injuries account for 15% to 20% of all military injuries and pose a high risk of causing functional disability and fatality. Blunt ballistic impacts are one of the threats that can lead to severe head injuries. This review aims to examine the mechanisms and injury risk assessment associated with blunt ballistic head injury (BBHI). The review further discusses research methods and instrumentation used in BBHI studies, focusing on their limitations and challenges. Studies on the mechanisms of focal and diffuse brain injuries remain largely inconclusive and require further efforts. Some studies have attempted to associate BBHIs with head mechanics, but more research is required to establish correlations between head mechanics and injury severity. Limited access to experimental models and a lack of instrumentation capable of measuring the mechanics of brain tissue in-situ are potential reasons for the lack of understanding of injury mechanisms, injury correlations and injury tolerance levels specific to this loading regime. Targeted research for understanding and assessing head injuries in blunt ballistic impacts is a necessary step in improving our ability to design protection systems to mitigate these injuries.

Assessment of Less Lethal Impact Munitions Using the Facial and Ocular CountermeasUre for Safety (FOCUS) Headform

Recent social protests and gatherings in the USA have prompted law enforcement agencies to increase their use of less lethal impact munitions (LLIMs) for crowd control. Media reports and firsthand accounts have indicated that many of the LLIMs are impacting individuals in the head and neck regions. There is very little data available on the risk of injury (ROI) from LLIM impacts to these body regions. The Facial and Ocular CountermeasUre for Safety (FOCUS) surrogate headform was used to assess the ROI (fracture) from LLIM impacts. LLIMs were fired at the FOCUS headform to determine the ROI to the frontal and maxilla bones. Sixteen different LLIMs were assessed which included 12-gauge, 37-mm, and 40-mm caliber projectiles from five manufacturers. The LLIMs included bean bag style, rubber, and foam/sponge projectiles. Each LLIM was tested multiple times to determine the average ROI. The average peak resultant frontal bone force ranged from 2.0 to 7.6 kN which represented ROIs from ~ 30% up to 95%. The average peak resultant maxilla bone force ranged from 1.0 to 4.4 kN which represented ROIs from ~ 30% up to 99%. In general, 12-gauge LLIMs had a lower ROI than the larger caliber LLIMs and the rubber projectiles had a lower ROI than the bean bag style projectiles. Due to the relative thickness, the maxilla has a much lower fracture force than the frontal bone, and this was borne out in the ROIs from the maxilla impacts. Impacts to both bones showed a positive correlation between normalized energy and resultant force (p  < 0.01). The slope of the plotted resultant force against the normalized energy for the 12-gauge munitions was significantly smaller compared to larger calibers for both impact sites, frontal (p  = 0.031), and maxilla (p  < 0.001).

Fracture Injury Risk of the Restrained Mandible to Anterior-Posterior Blunt Impacts

This study describes the results of anterior-posterior impacts conducted on the mandibles of 22 male postmortem human subjects (PMHSs). The objective of this study was to develop an injury criterion for the mandible based on blunt impact while the jaw was restrained. Previous studies have attempted to characterize the injury risk of blunt impact to the mandible; however, due to the translation of the mandible during impact and a limited number of fractured specimens, previous studies were not able to produce an injury criterion. Blunt impact to a restrained mandible is relevant to a wide array of helmeted individuals, including the military population and sports that require helmets with chinstraps. Therefore, in this study, specimens were positioned with restrained jaws and impacted using a monorail drop tower with a gravity-driven cylindrical impactor. Nineteen of 22 specimens sustained at least one fracture during testing. Injury cases had an average impact energy of 15.0 ± 5.7 J (11.1 ± 4.2 ft-lb) and a fracture force of 2684 ± 726 N (603 ± 163 lbf). Results were used to generate an impactor force based injury criterion through survival analysis. Risk of injury was modeled using a Weibull distribution and a 50% risk of injury was found to occur at approximately 2834 N (637 lbf). The developed injury risk curve can be used to characterize injury to the restrained mandible for future testing and research studies, especially in the development of maxillofacial protective equipment.

Ballistic impact response of a fluid/structure coupling-based modification of human thorax modelling

Studying the mechanical response of the human thorax submitted to ballistic impact is a challenging field of research. For ethical reasons, it is not possible to perform tests on the human body. Numerical simulations are therefore one of the alternatives for evaluating the mechanical response of the human thorax. In earlier research, a simplified human thorax submitted to low-velocity impacts without ballistic protection was modelled. Not all internal organs in the thorax were taken into account. The only considered organs were the heart, lungs, trachea and aorta, with the space between them being void. The organs were covered by an idealised structure simulating the rib cage, spine and muscles. Such a simplified model was however sufficient in the field of less-lethal impact assessment. Indeed, in this case, only forces and displacements are taken into account. In the field of behind armour blunt trauma (BABT), spherical pressure or shock waves are expected to appear and propagate into internal organs. Nevertheless, the presence of the void space makes it impossible to evaluate the propagation of the considered waves. This paper focuses on a method for filling the void space and making the model more comprehensive. Starting from the initial meshed geometry of this simulated thorax, it uses a coupling between Lagrangian and arbitrary Lagrangian-Eulerian (ALE) objects. Finally, the use of the filled model is extended to a BABT case study. From the simulations, it could be concluded that BABT should be related to "blast" instead of "viscous" solicitations.

Ophthalmic Injuries Related to Maxillofacial Trauma Due to Urban Warfare

: Midfacial trauma commonly causes ocular injuries of varying degrees. Eye injuries account for approximately 10% of all battle injuries. Severity of injuries may range from a subconjunctival haemorrhage to optic nerve injury and globe laceration and rupture.

AIM OF STUDY

Is to evaluate the associated ophthalmic injuries in maxillofacial trauma due to war and to emphasize the need for proper ophthalmic examination to exclude and manage any associated ophthalmic injuries.

MATERIALS AND METHODS

A total of 66 patients with maxillofacial trauma due to war were considered in this study and underwent classification of the fractures to know patterns of fractures and to specify the ophthalmic injuries which might be associated with each fracture. Referral to ophthalmologist was considered to determine the exact nature of ophthalmic injuries. Results by a maxillofacial surgeon and ophthalmologist were evaluated.

RESULTS

Midfacial trauma particularly those associated with zygomatic bone fracture was highly significant due to blast and bullets can lead to serious ophthalmic injuries. This was related to 57% of ophthalmic injuries. The related ocular injuries which were subconjunctival hemorrhage and the rupture or lacerated eye globe found to be highly significant war injuries while the preretinal hemorrhage and diplopia were significant.

CONCLUSION

A thorough proper ophthalmic examination should be carried out for every patient with these fractures and suspected cases should be placed under close observation so that immediate and active treatment can be taken if necessary.

The traumatic potential of a projectile shot from a sling

Herein, we analyze the energy parameters of stones of various weights and shapes shot from a sling and based on this data evaluate its traumatic potential. Four police officers proficient in the use of a sling participated in the trials. The following projectile types, shot using an overhead technique at a target 100m away were: round steel balls of different sizes and weights (24mm, 57g; 32mm, 135g; 38mm, 227g); different shaped stones weighing 100-150g and 150-200g and a golf ball (47g). Our data indicated that projectiles shot from unconventional weapons such as a sling, have serious traumatic potential for unprotected individuals and can cause blunt trauma of moderate to critical severity such as fractures of the trunk, limb, and facial skull bone, depending on the weight and shape of the projectile and the distance from the source of danger. Asymmetrically shaped projectiles weighing more than 100g were the most dangerous. Projectiles weighing more than 100g can cause bone fractures of the trunk and limbs at distances of up to 60m from the target and may cause serious head injuries to an unprotected person (Abbreviated Injury Scale 4-5) at distances up to 200m from the target. Due to the traumatic potential of projectiles shot from a sling, the police must wear full riot gear and keep at a distance of at least 60m from the source of danger in order to avoid serious injury. Furthermore, given the potential for serious head injuries, wearing a helmet with a visor is mandatory at distances up to 200m from the source of danger.

The surgical management of facial trauma in British soldiers during combat operations in Afghanistan

INTRODUCTION

The recent Afghanistan conflict caused a higher proportion of casualties with facial injuries due to both the increasing effectiveness of combat body armour and the insurgent use of the improvised explosive device (IED). The aim of this study was to describe all injuries to the face sustained by UK service personnel from blast or gunshot wounds during the highest intensity period of combat operations in Afghanistan.

METHODS

Hospital records and Joint Theatre Trauma Registry data were collected for all UK service personnel killed or wounded by blast and gunshot wounds in Afghanistan between 01 April 2006 and 01 March 2013.

RESULTS

566 casualties were identified, 504 from blast and 52 from gunshot injuries. 75% of blast injury casualties survived and the IED was the most common mechanism of injury with the mid-face the most commonly affected facial region. In blast injuries a facial fracture was a significant marker for increased total injury severity score. A facial gunshot wound was fatal in 53% of cases. The majority of survivors required a single surgical procedure for the facial injury but further reconstruction was required in 156 of the 375 of survivors aero medically evacuated to the UK.

CONCLUSIONS

The presence and pattern of facial fractures was significantly different in survivors and fatalities, which may reflect the power of the blast that these cohorts were exposed to. The Anatomical Injury Scoring of the Injury Severity Scale was inadequate for determining the extent of soft tissue facial injuries and did not predict morbidity of the injury.

Dynamic finite element simulation of the gunshot injury to the human forehead protected by polyvinyl alcohol sponge

Although there are some traditional models of the gunshot wounds, there is still a need for more modeling analyses due to the difficulties related to the gunshot wounds to the forehead region of the human skull. In this study, the degree of damage as a consequence of penetrating head injuries due to gunshot wounds was determined using a preliminary finite element (FE) model of the human skull. In addition, the role of polyvinyl alcohol (PVA) sponge, which can be used as an alternative to reinforce the kinetic energy absorption capacity of bulletproof vest and helmet materials, to minimize the amount of skull injury due to penetrating processes was investigated through the FE model. Digital computed tomography along with magnetic resonance imaging data of the human head were employed to launch a three-dimensional (3D) FE model of the skull. Two geometrical shapes of projectiles (steel ball and bullet) were simulated for penetrating with an initial impact velocity of 734 m/s using nonlinear dynamic modeling code, namely LS-DYNA. The role of the damaged/distorted elements were removed during computation when the stress or strain reached their thresholds. The stress distributions in various parts of the forehead and sponge after injury were also computed. The results revealed the same amount of stress for both the steel ball and bullet after hitting the skull. The modeling results also indicated the time that steel ball takes to penetrate into the skull is lower than that of the bullet. In addition, more than 21% of the steel ball's kinetic energy was absorbed by the PVA sponge and, subsequently, injury sternness of the forehead was considerably minimized. The findings advise the application of the PVA sponge as a substitute strengthening material to be able to diminish the energy of impact as well as the load transmitted to the object.

NUMERICAL ANALYSIS OF A PROJECTILE PENETRATION INTO THE HUMAN HEAD VIA MESHLESS METHOD

In recent years, physicists, engineers and medical scientists have tried to demonstrate the biomechanics of gunshot wounds with numerical methods and experimental observations. Currently, the finite element method (FEM) is the most widely used numerical method among the studies related to ballistic wound injuries. However, when the FEM is used for the penetration analysis, the path of the projectile in the skull is subjected to extremely large deformations which will introduce errors due to distortion of elements. To overcome this error, the meshfree technique was established to simulate the gunshot wound as a preliminary study in which the skull was modeled by smoothed particle hydrodynamics (SPH) and the projectile was modeled by nondeformable rigid elements. In order to simulate a realistic penetration phenomenon, orthotropic material properties were defined for different regions (forehead, zygomatic and mandible) with material principal axis along the surface of the bones.

Human response to the ballistics impacts were determined in terms of force occurring along the pathway of the bullet in the skull, residual velocity of the projectile and penetration depth. The obtained results were compared with the data reported in literature. As a result, mechanical behavior of the head under ballistic impacts simulated by the SPH, compared well with the results determined by the data given in literature, which indicates the applicability of the SPH method as a powerful technique in simulating different gunshot wound mechanisms.

An integrated helmet and neck support (iHANS) for racing car drivers: a biomechanical feasibility study

A new form of head and neck protection for racing car drivers is examined. The concept is one whereby the helmet portion of the system is attached, by way of a quick release clamp, to a collar-like platform which is supported on the driver's shoulders. The collar, which encircles the back and sides of the driver's neck, is held in place by way of the on-board restraint belts. The interior of the helmet portion of the assembly is large enough to provide adequate volitional head motion. The overall objective of the design is to remove the helmet from the wearer's head and thereby to mitigate the deleterious features of helmet wearing such as neck fatigue, poor ventilation and aerodynamic buffeting. Just as importantly, by transferring the weight of the helmet and all attendant reaction forces associated with inertial and impact loads to the shoulder complex (instead of to the neck), reduced head and neck injury probability should be achievable. This paper describes the concept development and the evolution of various prototype designs. Prototypes have been evaluated on track and sled tested in accordance with contemporary head neck restraint systems practice. Also discussed is a series of direct impact tests. In addition, low mass high velocity ballistic tests have been conducted and are reviewed herein. It is concluded that this new concept indeed does address most of the drawbacks of the customary helmet and that it generally can reduce the probability of head and neck injury.

Designing the ideal model for assessment of wound contamination after gunshot injuries: a comparative experimental study

Background

Modern high-velocity projectiles produce temporary cavities and can thus cause extensive tissue destruction along the bullet path. It is still unclear whether gelatin blocks, which are used as a well-accepted tissue simulant, allow the effects of projectiles to be adequately investigated and how these effects are influenced by caliber size.

Method

Barium titanate particles were distributed throughout a test chamber for an assessment of wound contamination. We fired .22-caliber Magnum bullets first into gelatin blocks and then into porcine hind limbs placed behind the chamber. Two other types of bullets (.222-caliber bullets and 6.5 × 57 mm cartridges) were then shot into porcine hind limbs. Permanent and temporary wound cavities as well as the spatial distribution of barium titanate particles in relation to the bullet path were evaluated radiologically.

Results

A comparison of the gelatin blocks and hind limbs showed significant differences (p < 0.05) in the mean results for all parameters. There were significant differences between the bullets of different calibers in the depth to which barium titanate particles penetrated the porcine hind limbs. Almost no particles, however, were found at a penetration depth of 10 cm or more. By contrast, gas cavities were detected along the entire bullet path.

Conclusion

Gelatin is only of limited value for evaluating the path of high-velocity projectiles and the contamination of wounds by exogenous particles. There is a direct relationship between the presence of gas cavities in the tissue along the bullet path and caliber size. These cavities, however, are only mildly contaminated by exogenous particles.

A new model for the characterization of infection risk in gunshot injuries: technology, principal consideration and clinical implementation

INTRODUCTION

The extent of wound contamination in gunshot injuries is still a topic of controversial debate. The purpose of the present study is to develop a model that illustrates the contamination of wounds with exogenous particles along the bullet path.

MATERIAL AND METHODS

To simulate bacteria, radio-opaque barium titanate (3-6 μm in diameter) was atomized in a dust chamber. Full metal jacket or soft point bullets caliber .222 (n = 12, v0 = 1096 m/s) were fired through the chamber into a gelatin block directly behind it. After that, the gelatin block underwent multi-slice CT in order to analyze the permanent and temporary wound cavity.

RESULTS

The permanent cavity caused by both types of projectiles showed deposits of barium titanate distributed over the entire bullet path. Full metal jacket bullets left only few traces of barium titanate in the temporary cavity. In contrast, the soft point bullets disintegrated completely, and barium titanate covered the entire wound cavity.

DISCUSSION

Deep penetration of potential exogenous bacteria can be simulated easily and reproducibly with barium titanate particles shot into a gelatin block. Additionally, this procedure permits conclusions to be drawn about the distribution of possible contaminants and thus can yield essential findings in terms of necessary therapeutic procedures.

Blunt Criterion trauma model for head and chest injury risk assessment of cal. 380 R and cal. 22 long blank cartridge actuated gundog retrieval devices

BACKGROUND

Blunt ballistic impact trauma is a current research topic due to the widespread use of kinetic energy munitions in law enforcement. In the civilian setting, an automatic dummy launcher has recently been identified as source of blunt impact trauma. However, there is no data on the injury risk of conventional dummy launchers. It is the aim of this investigation to predict potential impact injury to the human head and chest on the basis of the Blunt Criterion which is an energy based blunt trauma model to assess vulnerability to blunt weapons, projectile impacts, and behind-armor-exposures.

METHODS

Based on experimentally investigated kinetic parameters, the injury risk of two commercially available gundog retrieval devices (Waidwerk Telebock, Germany; Turner Richards, United Kingdom) was assessed using the Blunt Criterion trauma model for blunt ballistic impact trauma to the head and chest.

RESULTS

Assessing chest impact, the Blunt Criterion values for both shooting devices were higher than the critical Blunt Criterion value of 0.37, which represents a 50% risk of sustaining a thoracic skeletal injury of AIS 2 (moderate injury) or AIS 3 (serious injury). The maximum Blunt Criterion value (1.106) was higher than the Blunt Criterion value corresponding to AIS 4 (severe injury). With regard to the impact injury risk to the head, both devices surpass by far the critical Blunt Criterion value of 1.61, which represents a 50% risk of skull fracture. Highest Blunt Criterion values were measured for the Turner Richards Launcher (2.884) corresponding to a risk of skull fracture of higher than 80%.

CONCLUSION

Even though the classification as non-guns by legal authorities might implicate harmlessness, the Blunt Criterion trauma model illustrates the hazardous potential of these shooting devices. The Blunt Criterion trauma model links the laboratory findings to the impact injury patterns of the head and chest that might be expected.

Development of Biomechanical Response Corridors of the Head to Blunt Ballistic Temporo-Parietal Impact

There is a need to study the biomechanical response of the head to blunt ballistic impact. While the frequency of less-lethal munition impacts to the head may be less than other vital body regions, more serious injuries have been attributed to these impacts. This study aims to establish biomechanical response corridors for the temporo-parietal region for future development of biomechanical surrogate devices. Seven unembalmed post-mortem human subject specimens were exposed to blunt ballistic temporo-parietal head impact (103 g, 38 mm diameter impactor) to determine the force-time, deformation-time, and force-deformation responses. Comparisons were made to responses from prior blunt ballistic head impact studies, as well as automotive-related impact studies. Peak forces for impact condition A (19.5±2.6 m/s) were 3659±1248 N with deformations at peak force of 7.3±2.1 mm. Peak forces for impact condition B (33.6±1.4 m/s) were 5809±1874 N with deformations at peak force of 9.9±2.6 mm. Seven fractures were produced in the seven specimens. Depressed comminuted fracture types were documented in six of the seven cases. The average stiffness of the temporo-parietal region under blunt ballistic impact was 0.46±0.14 kN/mm. Stiffness results indicate that the response of the temporo-parietal region is similar to the forehead under blunt ballistic loading conditions. In addition, the response is significantly less stiff when compared with temporo-parietal impacts performed in automotive-related studies. These data provide the foundation for future research in the area of blunt ballistic head impact research including the development of biomechanical surrogates and computational models.

Tolerance of the skull to blunt ballistic temporo-parietal impact

Less-lethal ballistic projectiles are used by police personnel to temporarily incapacitate suspects. While the frequency of these impacts to the head is low, they account for more serious injuries than impacts to any other body region. As a result, there is an urgent need to assess the tolerance of the head to such impacts. The focus of this study was to investigate the tolerance of the temporo-parietal skull to blunt ballistic impact and establish injury criteria for risk assessment. Seven unembalmed isolated cadaver heads were subjected to fourteen impacts. Specimens were instrumented with a nine-accelerometer array as well as strain gages surrounding the impact site. Impacts were performed with a 38 mm instrumented projectile at velocities ranging from 18 to 37 m/s. CT images and autopsies were performed to document resulting fractures. Peak fracture force for the seven resulting fractures was 5633+/-2095 N. Peak deformation for fracture-producing impacts was 7.8+/-3.2 mm. The blunt criterion (BC), peak force and principal strain were determined to be the best predictors of depressed comminuted fractures. Temporo-parietal tolerance levels were consistent with previous studies. An initial force tolerance level of 2346 N is established for the temporo-parietal region for blunt ballistic impact with a 38 mm diameter impactor.

Air Bag-Induced Orbital Blow-Out Fractures

RATIONALE

Although air bags have decreased the risk of serious injury from motor vehicle crashes, their deployment is not innocuous and can result in injury. The force of the deploying air bag can cause orbital blow-out fractures. We investigated the circumstances that predispose a crash occupant to this particular injury.

STUDY DESIGN

The authors conducted a case series.

METHODS

A total of 150 orbital fractures occurred among 2,739 occupants in crashes included in the Crash Injury Research and Engineering Network (CIREN) database from January 1997 to July 2005. Ten orbital blow-out fractures attributed solely to air bag deployment were extracted and four reported in depth. Occupant, vehicle, and crash characteristics were reviewed for predisposing similarities and to investigate the mechanism of injury.

RESULTS

All crashes had air bag deployment and a frontal or near-frontal principle direction of force. Nine of 10 injured occupants were positioned within the air bag's deployment zone at the time of impact as a result of a forward seat track position, falling asleep at the wheel, being unrestrained, or having decelerated before impact. Six of 10 occupants experiencing orbital blow-out fractures were of shorter than average height. Based on rigorous crash reconstructions, the orbital blow-out injuries were felt to be causally related to air bag deployment.

CONCLUSION

Air bag deployment may result in orbital blow-out fractures. Occupants positioned in close proximity to the air bag during its deployment phase appear to be at increased risk for orbital blow-out fractures.

Vibrational analysis of mandible trauma: experimental and numerical approaches

The aim of this study was to evaluate the effectiveness of vibrational assessment of the mandible fracture patterns. Measurement of natural frequencies and associated vibrational mode shapes was performed to determine the relationship between the dynamic behavior of the human mandible and incidence of mandibular fractures using both in vitro modal testing and finite element analysis. Our results show that the natural frequencies of the human mandible in dry and wet conditions are 567 Hz and 501 Hz, respectively. The first vibrational mode of human mandible is a bending vibration with nodes located at the mandibular body where bone fracture is less likely to occur. By contrast, high vibration amplitudes were identified in the symphysis/parasymphysis and subcondyle regions where bone fractures tend occur. These findings indicate that the vibrational characteristics of the mandible are potential parameters for assessment of the mechanisms of injury.