Chris A. Van Ee

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.

On the Structural and Material Properties of Mammalian Skeletal Muscle and Its Relevance to Human Cervical Impact Dynamics

The absence of data on the material properties of skeletal muscle has resulted in limitations in the utility of human surrogates in evaluating injury potential during head and neck impact. The purpose of this paper is two fold. First, a quasi-linear viscoelastic model is developed to describe and predict the passive structural response of the New Zealand White rabbit tibialis anterior muscle. Second, the constitutive properties of skeletal muscle and the effect of elongation rate on these properties are determined for both the passive and stimulated states of the muscle. A review of the literature, and recommendations for modeling the effects of skeletal muscle on cervical spine impact dynamics are discussed. Language: en

THE EFFECT OF POSTMORTEM TIME AND FREEZER STORAGE ON THE MECHANICAL PROPERTIES OF SKELETAL MUSCLE

Data is currently lacking to define the state of skeletal muscle properties within the cadaver. This study sought to define changes in the postmortem properties of skeletal muscle as a function of mechanical loading and freezer storage. The tibialis anterior of the New Zealand White rabbit was chosen for study. Modulus and no-load strain were found to vary greatly from live after 8 hours postmortem. Following the dynamic changes that occur at the onset and during rigor mortis, a semi-stable region of postmortem, post-rigor properties occurred between 36 to 72 hours postmortem. A freeze-thaw process was not found to have a significant effect on the post-rigor response. The first loading cycle response of post-rigor muscle was unrepeatable but stiffer than live passive muscle. After preconditioning, the post-rigor muscle response was repeatable but significantly less stiff than live passive muscle due to an increase in no-load strain. Failure properties of postmortem muscle were found to be significantly different than live passive muscle with significant decreases in failure stress (61%) and energy (81%), while failure strain was unchanged. Results suggest that the post-rigor response of cadaver muscle is unaffected by freezing but sensitive to even a few cycles of mechanical loading.

Exploring the Role of Lateral Bending Postures and Asymmetric Loading on Cervical Spine Compression Responses

In an effort to expand the understanding of head and neck injury dynamics in rollover type crashes, this investigation explores the influence of lateral bending postures and asymmetric compressive loads on the head and cervical spine. Drop testing of five male cadaver head-neck complexes was conducted with either an initial lateral bending posture onto a horizontal impact surface or with an initial neutral posture onto an obliquely oriented surface resulting in lateral bending. Five specimens were dropped from 0.45 and 0.53 m, with resulting impact speeds ranging from 2.9 to 3.25 m/s. Radiography of the specimens was performed pre- and post-testing to document any fractures. Three of the five specimens sustained compressive cervical vertebral fractures at lower neck loads ranging between 1518 N and 3472 N. Fracture patterns did suggest that the asymmetric postures and loading resulted in asymmetric fracture patterns. Overall compressive neck injury dynamics and tolerances appear similar to previous studies of purely sagittal plane dynamics based on these initial results. This study lays a foundation for quantifying the non-sagittal plane compressive response and tolerance of the cervical spine.Copyright

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.

High-Speed Biaxial Tissue Properties of the Human Cadaver Aorta

Traumatic rupture of the aorta (TRA) is one of the leading causes of mortality in automobile crashes. Finite element (FE) modeling, used in conjunction with laboratory experiments, has emerged as increasingly important tool to understand the mechanisms of TRA. Appropriate material modeling of the aorta is a key aspect of such efforts. The current study focuses on obtaining biaxial mechanical properties of aorta tissue at strain rates typically experienced during automotive crashes. Five descending thoracic aorta samples from human cadavers were harvested in a cruciate shape. The samples were subjected to equibiaxial stretch at a strain rate of 44 s−1 using a new biaxial tissue-testing device. Inertially compensated loads were measured. High-speed videography was used to track ink dots marked on the center of each sample to obtain strain. The aorta tissue exhibited anisotropic and nonlinear behavior. The tissue was stiffer in the circumferential direction with a modulus of 10.64 MPa compared to 7.94 MPa in longitudinal direction. The peak stresses along the circumferential and longitudinal directions were found to be 1.89 MPa and 1.76 MPa, respectively. The tissue behavior can be used to develop a better constitutive representation of the aorta, which can be incorporated into FE models of the aorta.Copyright

A new device for high-speed biaxial tissue testing : Application to traumatic rupture of the aorta

A biaxial test device was designed to obtain the material properties of aortic tissue at rates consistent with those seen in automotive impact. Fundamental to the design are four small tissue clamps used to grasp the ends of the tissue sample. The applied load at each clamp is determined using subminiature load cells in conjunction with miniature accelerometers for inertial compensation. Four lightweight carriages serve as mounting points for each clamp. The carriages ride on linear shafts, and are equipped with low-friction bearings. Each carriage is connected to the top of a central drive disk by a rigid link. A fifth carriage, also connected to the drive disk by a rigid link, is attached at the bottom. A pneumatic cylinder attached to the lower carriage initiates rotation of the disk. This produces identical motion of the upper carriages in four directions away from the disk center. Initial slack in a low-stretch, high-strength rope that connects the cylinder to the lower carriage allows the cylinder to achieve the desired test speed before initiating motion in the carriages. Two lasers, focused on the top and bottom surfaces of the tissue samples measure sample thickness throughout a given test.

CHILD ATD RECONSTRUCTION OF A FATAL PEDIATRIC FALL

The current head Injury Assessment Reference Values (IARVs) for the child dummies are based in part on scaling adult and animal data and on reconstructions of real world accident scenarios. Reconstruction of well-documented accident scenarios provides critical data in the evaluation of proposed IARV values, but relatively few accidents are sufficiently documented to allow for accurate reconstructions. This reconstruction of a well documented fatal-fall involving a 23-month old child supplies additional data for IARV assessment. The videotaped fatal-fall resulted in a frontal head impact onto a carpet-covered cement floor. The child suffered an acute right temporal parietal subdural hematoma without skull fracture. The fall dynamics were reconstructed in the laboratory and the head linear and angular accelerations were quantified using the CRABI-18 Anthropomorphic Test Device (ATD). Peak linear acceleration was 125 ± 7 g (range 114–139), HIC15 was 335 ± 115 (Range 257–616), peak angular velocity was 57± 16 (Range 26–74), and peak angular acceleration was 32 ± 12 krad/s2 (Range 15–56). The results of the CRABI-18 fatal fall reconstruction were consistent with the linear and rotational tolerances reported in the literature. This study investigates the usefulness of the CRABI-18 anthropomorphic testing device in forensic investigations of child head injury and aids in the evaluation of proposed IARVs for head injury.Copyright

Biomechanics of temporo-parietal skull fracture from blunt ballistic impact

The majority of engineering studies that quantify the biomechanical tolerance of the human skull to blunt impacts have been focused primarily on replicating automotive-related trauma [1]. Relatively little biomechanical data exists on skull fracture tolerance due to impacts with small surface area objects moving at high velocity, previously defined as blunt, ballistic impacts [2]. These impacts can occur with the deployment of less-lethal kinetic energy munitions that are now available to police and military personnel. The goal of less-lethal munitions is to impart sufficient force to a subject to deter uncivil, or hazardous, behavior with minimal risk for serious or fatal injury. A basic understanding of human biomechanical response and tolerance to blunt ballistic impact is needed for all areas of the human body in order to guide the design of such munitions. Law enforcement are trained to direct such munitions away from the head and at body regions such as the legs, however impacts to the head have occurred [3]. Previous research efforts have investigated facial impact tolerance to blunt ballistic impacts [4] however data regarding the temporo-parietal region are lacking. The goal of this research project is to provide basic bone strain data on temporo-parietal skull fracture for the purpose of developing finite element models of the human skull and fracture criterion for future study of blunt ballistic head impact.Copyright

The effect of soft tissue on the biomechanics of skull fracture due to blunt ballistic impact: Preliminary analysis and findings

The majority of engineering studies that quantify the biomechanical response of the human head to blunt impacts have been focused primarily on replicating automotive-related trauma [1]. Relatively little biomechanical data exists on head response and skull fracture tolerance due to impacts with small surface area objects moving at high velocity, as can occur with the deployment of less-lethal kinetic energy munitions that are now available to police and military personnel. Law enforcement are trained to direct such munitions away from the head and at body regions least likely to sustain serious to life-threatening injury, such as the legs, however impacts to vital regions such as the head have occurred [2]. Previous research efforts have investigated facial impact response to blunt ballistic impacts however data regarding the temporo-parietal region are lacking and require study under these unique loading conditions [3]. Prior research has indicated that the scalp and soft tissue covering the skull are important factors to consider when studying impact response and skull fracture tolerance [4]. These data however have been limited primarily to impact velocities typical of the automotive crash environment. The purpose of this study is to evaluate the contribution of soft tissue to the biomechanical response and tolerance of the temporo-parietal region under blunt ballistic impact conditions.Copyright