Crash characteristics and injury patterns of restrained front seat occupants in far-side impacts.

OBJECTIVE: The study was conducted to determine the association between vehicle-, crash-, and demographic-related factors and injuries to front seat far-side occupants in modern environments. METHODS: Field data were obtained from the NASS-CDS database for the years 2009-2012. Inclusion factors included the following: adult restrained front outboard-seated occupants, no ejection or rollovers, and vehicle model years less than 10 years old at the time of crash. Far-side crashes were determined by using collision deformation classification. Injuries were scored using the Abbreviated Injury Scale (AIS). Injuries (MAIS 2+, MAIS 3+, M denotes maximum score) were examined based on demographics, change in velocity, vehicle type, direction of force, extent zone, collision partner, and presence of another occupant in the front seat. Only weighted data were used in the analysis. Injuries to the head and face, thorax, abdomen, pelvis, and upper and lower extremity regions were studied. Odds ratios and upper and lower confidence intervals were estimated from multivariate analysis. RESULTS: Out of 519,195 far-side occupants, 17,715 were MAIS 2+ and 4,387 were MAIS 3+ level injured occupants. The mean age, stature, total body mass, and body mass index (BMI) were 40.7 years, 1.7 m, 77.2 kg, and 26.8 kg/m2, respectively. Of occupants with MAIS 2+ injuries, 51% had head and 19% had thorax injuries. Of occupants with MAIS 3+ injuries, 50% had head and 69% had thorax injuries. The cumulative distribution of changes in velocities at the 50th percentile for the struck vehicle for all occupants and occupants with MAIS 2+ and MAIS 3+ injuries were 19, 34, and 42 km/h, respectively. Furthermore, 73% of MAIS 2+ injuries and 86% of MAIS 3+ injuries occurred at a change in velocity of 24 km/h or greater. Odds of sustaining MAIS 2+ and MAIS 3+ injuries increased with each unit increase in change in velocity, stature, and age, with one exception. Odds of sustaining injuries were higher with the presence of an occupant in the front seat at the MAIS 3+ level, although it was reversed at the lower level. The extent zone of 3+ increased the odds compared to the extent zones of 1 to 2 at both MAIS 2+ and MAIS 3+ injuries. Odds ratios and confidence intervals are given. CONCLUSIONS: The findings are as follows: head and thorax are the more frequently injured body regions, and the prevalence of cranium injuries is similar at both injury severities; thoracic injuries are more prevalent at the MAIS 3+ level; the presence of another front seat occupant plays a role in MAIS 3+ trauma; injuries continue to occur at changes in velocity representative of side impact environments; and mean demographic factors are close to mid-size automotive anthropometry, indicating the need to pursue this line of study. Because data were gathered from only 4 years, it would be important to include additional NASS-CDS database years, rescore injuries from previous years, and analyze other international databases to reinforce these findings for advancing safety for far-side occupants.

Thoracolumbar spine fractures in frontal impact crashes.

There is currently no injury assessment for thoracic or lumbar spine fractures in the motor vehicle crash standards throughout the world. Compression-related thoracolumbar fractures are occurring in frontal impacts and yet the mechanism of injury is poorly understood. The objective of this investigation was to characterize these injuries using real world crash data from the US-DOT-NHTSA NASS-CDS and CIREN databases. Thoracic and lumbar AIS vertebral body fracture codes were searched for in the two databases. The NASS database was used to characterize population trends as a function of crash year and vehicle model year. The CIREN database was used to examine a case series in more detail. From the NASS database there were 2000-4000 occupants in frontal impacts with thoracic and lumbar vertebral body fractures per crash year. There was an increasing trend in incidence rate of thoracolumbar fractures in frontal impact crashes as a function of vehicle model year from 1986 to 2008; this was not the case for other crash types. From the CIREN database, the thoracolumbar spine was most commonly fractured at either the T12 or L1 level. Major, burst type fractures occurred predominantly at T12, L1 or L5; wedge fractures were most common at L1. Most CIREN occupants were belted; there were slightly more females involved; they were almost all in bucket seats; impact location occurred approximately half the time on the road and half off the road. The type of object struck also seemed to have some influence on fractured spine level, suggesting that the crash deceleration pulse may be influential in the type of compression vector that migrates up the spinal column. Future biomechanical studies are required to define mechanistically how these fractures are influenced by these many factors.

Injuries caused by brake pedal loading of the midfoot.

In a frontal car crash, the driver’s foot and ankle may be injured due to loading by the brake pedal. The driver of a vehicle often has time to initiate emergency braking before an impending collision, which places the forefoot or midfoot over the brake pedal. During the crash, the pedal may induce dorsiflexion and axial loading of the ankle due to forward motion of the occupant and rearward intrusion of the pedal relative to the vehicle. In order to investigate the injuries caused by pedal loading, impact tests were conducted on three cadaveric lower limbs. The limbs were braced at the knee, and a pedal positioned beneath the midfoot was driven towards the knee, inducing dorsiflexion and axial loading of the cadaveric limb. Ankle injury was generated in two specimens. Both injured limbs sustained a medial malleolar fracture, and one limb also suffered a talar neck fracture. These results suggest that pedal loading may be an important injury mechanism for fractures of the medial malleolus and talar neck in drivers involved in frontal crashes.

Thoraco-abdominal deflection responses of post mortem human surrogates in side impacts.

The objective of the present study was to determine the thorax and abdomen deflections sustained by post mortem human surrogate (PMHS) in oblique side impact sled tests and compare the responses and injuries with pure lateral tests. Oblique impact tests were conducted using modular and non-modular load-wall designs, with the former capable of accommodating varying anthropometry. Tests were conducted at 6.7 m/s velocity. Deflection responses from chestbands were analyzed from 15 PMHS tests: five each from modular load-wall oblique, non-modular load-wall oblique and non-modular load- wall pure lateral impacts. The thorax and abdomen peak deflections were greater in non-modular load-wall oblique than pure lateral tests. Peak abdomen deflections were statistically significantly different while the upper thorax deflections demonstrated a trend towards significance. Deflection angulations were statistically significantly different between pure lateral and oblique tests at all regions indicating that it is important to characterize not only the amplitude but also the angle of the vector. Injuries were confined to skeletal regions in pure lateral tests and this was in contrast to the occurrence of both skeletal and soft tissue/organ injury in oblique loading tests, again emphasizing the role of obliqueness in side impacts. Furthermore, injuries in oblique tests were primarily unilateral, paralleling real-world trauma and confirming the applicability of the experimental design to field environments. Potential injury mechanisms are discussed based on anatomical considerations. These findings, albeit from a limited sample size, underscore the need for additional studies to derive human injury tolerance and criteria in oblique side impacts.

BioTab--a new method for analyzing and documenting injury causation in motor-vehicle crashes.

OBJECTIVE: To describe a new method for analyzing and documenting the causes of injuries in motor vehicle crashes that has been implemented since 2005 in cases investigated by the Crash Injury Research Engineering Network (CIREN). METHODS: The new method, called BioTab, documents injury causation using evidence from in-depth crash investigations. BioTab focuses on developing injury causation scenarios (ICSs) that document all factors considered essential for an injury to have occurred as well as factors that contributed to the likelihood and/or severity of an injury. The elements of an injury causation scenario are (1) the source of the energy that caused the injury, (2) involved physical components (IPCs) contacted by the occupant that are considered necessary for the injury to have occurred, (3) the body region or regions contacted by each IPC, (4) the internal paths between body regions contacted by IPCs and the injured body region, (5) critical intrusions of vehicle components, and (6) factors that contributed to the likelihood and/or the severity of injury. RESULTS: Advantages of the BioTab method are that it attempts to identify all factors that cause or contribute to clinically significant injuries, allows for coding of scenarios where one injury causes another injury, associates injuries with a source of energy and allows injuries to be associated with sources of energy other than the crash, such as air bag deployment energy, allows for documenting scenarios where an injury was caused by two different body regions contacting two different IPCs, identifies and documents the evidence that supports ICSs and IPCs, assigns confidence levels to ICSs and IPCs based on available evidence, and documents body region and organ/component-level "injury mechanisms" and distinguishes these mechanisms from ICSs. CONCLUSION: The BioTab method provides for methodical and thorough evidenced-based analysis and documentation of injury causation in motor vehicle crashes.

The line of action in the tibia during axial compression of the leg.

Compression of the leg induces bending in the tibia, which can lead to tensile failure of the bone in the midshaft. The purpose of this study was to determine the orientation of the compressive load vector in the human tibia. Five cadaveric lower extremities were instrumented with in situ 6-axis tibial and fibular load cells and subjected to quasistatic axial leg compression tests in two knee positions and nine ankle positions. For each test, the location and angle of the line of action were calculated at the tibial midshaft. The line of action was extended to the bone ends in order to determine the locations of the effective centers of pressure on the tibial plafond and tibial plateau. The effective center of pressure on the tibial plafond consistently migrated anteriorly in dorsiflexion, laterally in eversion, posteriorly in plantarflexion, and medially in inversion. An opposite pattern was observed on the tibial plateau. When the knee was flexed, the effective center of pressure was generally isolated to a small area in the posterior portion of the medial tibial condyle. The percentage of the axial load borne by the fibula varied from -8% to 19%, and was related to the inversion/eversion angle of the ankle (p<0.02), as well as the distance between the fibula and the axial load path at the midshaft (p<0.001). The line of action through the tibia appeared to follow the external load path to the extent allowed by the available joint contact surfaces.

The effect of tibial curvature and fibular loading on the tibia index.

The tibia index (TI) is commonly used to predict leg injury based on measurements taken by an anthropomorphic test device (ATD). The TI consists of an interaction formula that combines axial loading and bending plus a supplemental compressive force criterion. Current ATD lower limbs lack geometric biofidelity with regard to tibial curvature and fibular load-sharing. Due to differences in tibial curvature, the midshaft moments induced by axial loading are different in humans and ATDs. Midshaft tibial loading in the human is also reduced by load-sharing through the fibula, which is not replicated in current ATDs. In this study, tibial curvature and fibular load-sharing are quantified through CT imaging and biomechanical testing, and equations are presented to correct ATD measurements to reflect the loading that would be experienced by a human tibia.

Small female head and neck interaction with a deploying side airbag.

OBJECTIVE: This paper presents dummy and cadaver experiments designed to investigate the injury potential of an out-of-position small female head and neck from a deploying side airbag. METHODS: Seat-mounted, thoracic-type, side airbags were selected for this study to represent those currently available on selected luxury automobiles. A computer simulation program was used to identify the worst case loading position for the small female head and neck. Once the initial position was identified, experiments were performed with the Hybrid III 5th percentile dummy and three small female cadavers, using three different inflators. RESULTS: Peak head center of gravity (CG) accelerations for the dummy ranged from 71x g to 154 x g, and were greater than cadaver values, which ranged from 68 x g to 103 x g. Peak neck tension as measured at the upper load cell of the dummy increased with inflator aggressivity from 992 to 1670N. A conservative modification of the US National Highway Traffic Safety Administration's (NHTSA's) N(ij) proposed neck injury criteria, which combines neck tension and bending, was used. All values were well below the 1.0 injury threshold for the dummy and suggested a very low possibility of neck injury. In agreement with this prediction, no injuries were observed. CONCLUSIONS: Even in a worst case position, small females are at low risk of head or neck injuries under loading from these thoracic-type airbags; however, injury risk increases with increasing inflator aggressivity.