Asphyxia in Motor Vehicle Crashes: Analysis of Crash-Related Variables Using National Automotive Sampling System Crashworthiness Data System and Forensic Case Studies.

Rates of death because of asphyxia in motor vehicle crashes have been previously estimated using county and statewide data sets, but national estimates have not been reported. The literature regarding asphyxia in motor vehicle crashes primarily involves discussions about clinical findings, and crash-related variables have been sparsely reported. The current study calculated a nationwide fatality rate for asphyxia in motor vehicle crashes of 1.4%. Seventeen case studies of asphyxia were also reported providing crash-, vehicle-, and occupant-related variables. These included type of accident, crash severity, seat belt use, containment status, extent of occupant compartment intrusion, height, weight, and injury pattern. The data presented can be used to better understand the injury mechanism, identify risk factors, develop possible protective countermeasures, and create situational awareness for emergency responders and investigators.

A new PMHS model for lumbar spine injuries during vertical acceleration.

Ejection from military aircraft exerts substantial loads on the lumbar spine. Fractures remain common, although the overall survivability of the event has considerably increased over recent decades. The present study was performed to develop and validate a biomechanically accurate experimental model for the high vertical acceleration loading to the lumbar spine that occurs during the catapult phase of aircraft ejection. The model consisted of a vertical drop tower with two horizontal platforms attached to a monorail using low friction linear bearings. A total of four human cadaveric spine specimens (T12-L5) were tested. Each lumbar column was attached to the lower platform through a load cell. Weights were added to the upper platform to match the thorax, head-neck, and upper extremity mass of a 50th percentile male. Both platforms were raised to the drop height and released in unison. Deceleration characteristics of the lower platform were modulated by foam at the bottom of the drop tower. The upper platform applied compressive inertial loads to the top of the specimen during deceleration. All specimens demonstrated complex bending during ejection simulations, with the pattern dependent upon the anterior-posterior location of load application. The model demonstrated adequate inter-specimen kinematic repeatability on a spinal level-by-level basis under different subfailure loading scenarios. One specimen was then exposed to additional tests of increasing acceleration to induce identifiable injury and validate the model as an injury-producing system. Multiple noncontiguous vertebral fractures were obtained at an acceleration of 21 g with 488 g/s rate of onset. This clinically relevant trauma consisted of burst fracture at L1 and wedge fracture at L4. Compression of the vertebral body approached 60% during the failure test, with -6,106 N axial force and 168 Nm flexion moment. Future applications of this model include developing a better understanding of the vertebral injury mechanism during pilot ejection and developing tolerance limits for injuries sustained under a variety of different vertical acceleration scenarios.

Axial head rotation increases facet joint capsular ligament strains in automotive rear impact.

Axial head rotation prior to low speed automotive rear impacts has been clinically identified to increase morbidity and symptom duration. The present study was conducted to determine the effect of axial head rotation on facet joint capsule strains during simulated rear impacts. The study was conducted using a validated intact head to first thoracic vertebra (T1) computational model. Parametric analysis was used to assess effects of increasing axial head rotation between 0 and 60° and increasing impact severity between 8 and 24 km/h on facet joint capsule strains. Rear impacts were simulated by horizontally accelerating the T1 vertebra. Characteristics of the acceleration pulse were based on the horizontal T1 acceleration pulse from a series of simulated rear impact experiments using full-body post mortem human subjects. Joint capsule strain magnitudes were greatest in ipsilateral facet joints for all simulations incorporating axial head rotation (i.e., head rotation to the left caused higher ligament strain at the left facet joint capsule). Strain magnitudes increased by 47-196% in simulations with 60° head rotation compared to forward facing simulations. These findings indicate that axial head rotation prior to rear impact increases the risk of facet joint injury.

Incorporation of lower neck shear forces to predict facet joint injury risk in low-speed automotive rear impacts.

Lower neck shear force remains a viable candidate for a low-velocity automotive rear-impact injury criterion. Data were previously reported to demonstrate high correlations between the magnitude of lower neck shear force and lower cervical spine facet joint motions. The present study determined the ability of lower neck shear force to predict soft-tissue injury risk in simulated automotive rear impacts. Rear-impact tests were conducted at two velocities and with two seatback orientations using a Hybrid III anthropomorphic test device (ATD) and stock automobile seats from 2007 model year vehicles. Higher velocities and more vertical seatback orientations were associated with higher injury risk based on computational modeling simulations performed in this study. Six cervical spine injury criteria including NIC, Nij, Nkm, LNL, and lower neck shear force and bending moment, increased with impact velocity. NIC, Nij, and shear force were most sensitive to changes in impact velocity. Four metrics, including Nkm, LNL, and lower neck shear force and bending moment, increased for tests with more vertical seatback orientations. Shear force was most sensitive to changes in seatback orientation. Peak values for shear force, NIC, and Nij occurred approximately at the time of head restraint contact for all four test conditions. Therefore, of the six investigated metrics, lower neck shear force was the only metric to demonstrate consistency with regard to injury risk and timing of peak magnitudes. These results demonstrate the ability of lower neck shear force to predict injury risk during low velocity automotive rear impacts and warrant continued investigation into the sensitivity and applicability of this metric for other rear-impact conditions.

Population-based estimates of whiplash injury using nass cds data - biomed 2009.

Clinical investigations identified occupant-related factors that may predispose specific populations to increased whiplash injury susceptibility. However, clinical studies represent a specific patient population and are not representative of the population at large. The present objective was to analyze nationally-representative data to assess the association between gender and whiplash in motor vehicle rear-end impacts. A cohort of front-seat occupants in rear impacts (5-7 o'clock) from 1998-2007 were acquired using the National Automotive Sampling System (NASS) Crashworthiness Data System database. Outcome measure was "cervical spine strain" without fracture or dislocation, coded as 640278.1. Differences between injured population proportions were analyzed using Chi-Square test of independence. 1,973 rear impacts were selected, representing 936,439 weighted crashes from across the United States. Females accounted for 69% of the weighted whiplash injuries, and the proportion of females sustaining whiplash was 10% higher than males. Furthermore, gender was associated with acquiring whiplash in rear impacts (odds ratio for females: 2.16; 95% confidence interval: 1.5-3.1). Although NASS data is inherently weighted toward more severe impacts (i.e., tow-away collisions), this population-based study has demonstrated increased female susceptibility to whiplash injury. The importance of gender suggests that specific safety measures for female front-seat occupants should be addressed separately from males.