Sex-related disparities in vehicle crash injury and hemodynamics

Objective

Multiple studies evaluate relative risk of female vs. male crash injury; clinical data may offer a more direct injury-specific evaluation of sex disparity in vehicle safety. This study sought to evaluate trauma injury patterns in a large trauma database to identify sex-related differences in crash injury victims.

Methods

Data on lap and shoulder belt wearing patients age 16 and up with abdominal and pelvic injuries from 2018 to 2021 were extracted from the National Trauma Data Bank for descriptive analysis using injuries, vital signs, International Classification of Disease (ICD) coding, age, and injury severity using AIS (Abbreviated Injury Scale) and ISS (Injury Severity Score). Multiple linear regression was used to assess the relationship of shock index (SI) and ISS, sex, age, and sex*age interaction. Regression analysis was performed on multiple injury regions to assess patient characteristics related to increased shock index.

Results

Sex, age, and ISS are strongly related to shock index for most injury regions. Women had greater overall SI than men, even in less severe injuries; women had greater numbers of pelvis and liver injuries across severity categories; men had greater numbers of injury in other abdominal/pelvis injury regions.

Conclusions

Female crash injury victims' tendency for higher (AIS) severity of pelvis and liver injuries may relate to how their bodies interact with safety equipment. Females are entering shock states (SI > 1.0) with lesser injury severity (ISS) than male crash injury victims, which may suggest that female crash patients are somehow more susceptible to compromised hemodynamics than males. These findings indicate an urgent need to conduct vehicle crash injury research within a sex-equity framework; evaluating sex-related clinical data may hold the key to reducing disparities in vehicle crash injury.

Analysis of experimental injuries to obese occupants with different postures in frontal impact

The objective of the present study was to analyze injuries and their patterns to obese occupants in frontal impacts with upright and reclined postures using experimental data. Twelve obese post-mortem human subjects (PMHS) were positioned on a sled buck with seatback angles of 250 or 450 from the vertical, termed as upright and reclined postures. They were restrained with a seat belt and pretensioner. Frontal impact tests were conducted at 8.9 or 13.9 m/s, termed as low and high velocities. After the test, x-rays and CTs were taken, and an autopsy was conducted. The Maximum AIS (MAIS) and Injury Severity Score (ISS) were calculated, and injury patterns were analyzed. The mean age, stature, total body mass, and body mass indexes were 67 years, 112 kg, and 1.7 m, and 38 kg/m2. None of these parameters were statistically significantly different between any groups. The mean thickness of the soft tissues in the left anterior lateral, central, and right anterior lateral aspects were 44 mm, 24 mm, and 46 mm. In the low-velocity tests, the ISS data were 9, 18, and 9 for the upright, and 9, 9, and 4 for the reclined specimens, and in the high velocity tests, they were 29, 17, and 27 for the upright, and 27, 13, and 27 for the reclined postures. Other data are given in the paper. For both postures at the low velocity, injuries were concentrated at one body region, and the ISS data were in the mild category; in contrast, at the high velocity, other body regions also sustained injuries, and the ISS data were in the major trauma category. From MAIS perspectives, injuries to obese occupants did not change between postures and were independent of the energy input to the system. The association of chest with pelvis injuries in upright and reclined postures to obese occupants may have additional consequences following the initial injury to this group of our population.

Pelvis-Sacrum-Lumbar Spine Injury Characteristics From Underbody Blast Loading

INTRODUCTION

Combat-related injuries from improvised explosive devices occur commonly to the lower extremity and spine. As the underbody blast impact loading traverses from the seat to pelvis to spine, energy transfer occurs through deformations of the combined pelvis-sacrum-lumbar spine complex, and the time factor plays a role in injury to any of these components. Previous studies have largely ignored the role of the time variable in injuries, injury mechanisms, and warfighter tolerance. The objective of this study is to relate the time or temporal factor using a multi-component, pelvis-sacrum-lumbar spinal column complex model.

MATERIALS AND METHODS

Intact pelvis-sacrum-spine specimens from pre-screened unembalmed human cadavers were prepared by fixing at the superior end of the lumbar spine, pelvis and abdominal contents were simulated, and a weight was added to the cranial end of the fixation to account for torso effective mass. Prepared specimens were placed on the platform of a custom vertical accelerator device and aligned in a seated soldier posture. An accelerometer was attached to the seat platen of the device to record the time duration to peak velocity. Radiographs and computed tomography images were used to document and associate injuries with time duration.

RESULTS

The mean age, stature, weight, body mass index, and bone density of 12 male specimens were as follows: 65 ± 11 years, 1.8 ± 0.01 m, 83 ± 13 kg, 27 ± 5.0 kg/m2, and 114 ± 21 mg/cc. They were equally divided into short, medium, and long time durations: 4.8 ± 0.5, 16.3 ± 7.3, and 34.5 ± 7.5 ms. Most severe injuries associated with the short time duration were to pelvis, although they were to spine for the long time duration.

CONCLUSIONS

With adequate time for the underbody blast loading to traverse the pelvis-sacrum-spine complex, distal structures are spared while proximal/spine structures sustain severe/unstable injuries. The time factor may have implications in seat and/or seat structure design in future military vehicles to advance warfighter safety.

THOR-05F biofidelity evaluation in reclined and upright seated postures subjected to frontal crash pulses

The THOR 5th percentile female dummy (THOR-05F) was evaluated for two seating postures/positions in frontal impacts using a generic automotive seat environment. The conditions included 2 crash pulses: a 15 km/h test that utilized 4.5 g acceleration and a 3-point restraint with 2 kN load limiter, and a 32 km/h test that utilized 9.5 g acceleration and a 3-point restraint with a 4.5 kN load limiter and pretensioner, and two seatback angles: 25°, a nominal upright posture, and 45°, a moderate reclined posture. The BRS scores were calculated using the NHTSA BioRank method. Overall biofidelity rating was consider excellent for both seating postures. This evaluation provides an understanding of the THOR-05F response and biofidelity evaluation of the ATD in two seating postures (nominal and reclined). This is essential in the assessment and development of safety measures in emerging ADS-equipped vehicles.

Temporal corridors of forces and moments, and injuries to pelvis-lumbar spine in vertical impact simulating underbody blast

Pelvis and lumbar spine fractures occur in falls, motor vehicle crashes, and military combat events. They are attributed to vertical impact from the pelvis to the spine. Although whole-body cadavers were exposed to this vector and injuries were reported, spinal loads were not determined. While previous studies determined injury metrics such as peak forces using isolated pelvis or spine models, they were not conducted using the combined pelvis-spine columns, thereby not accounting for the interaction between the two body regions. Earlier studies did not develop response corridors. The study objectives were to develop temporal corridors of loads at the pelvis and spine and assess clinical fracture patterns using a human cadaver model. Vertical impact loads were delivered at the pelvic end to twelve unembalmed intact pelvis-spine complexes, and pelvis forces and spinal loads (axial, shear and resultant and bending moments) were obtained. Injuries were classified using clinical assessments from post-test computed tomography scans. Spinal injuries were stable in eight and unstable in four specimens. Pelvis injuries included ring fractures in six and unilateral pelvis in three, sacrum fractures in ten, and two specimens did not sustain any injuries to the pelvis or sacrum complex. Data were grouped based on time to peak velocity, and ± one standard deviation corridors about the mean of the biomechanical metrics were developed. Time-history corridors of loads at the pelvis and spine, hitherto not reported in any study, are valuable to assess the biofidelity of anthropomorphic test devices and assist validating finite element models.

Influence of bending pre-load on the tensile response of the lumbar spine

Previous full body cadaver testing has shown that both obliquely oriented seats in survivable aircraft crashes and far-side oblique crashes in vehicles present distinctive occupant kinematics that are not yet well understood. Knowledge surrounding how these loading scenarios affect the lumbar spine is particularly lacking as there exists minimal research concerning oblique loading. The current study was created to evaluate a novel experimental method through comparison with existing literature, and to examine the impact of a static bending pre-load (posture) on the load-displacement response for the whole lumbar spine loaded in non-destructive axial distraction. T12-S1 lumbar spines were tested in tension to 4 mm of displacement while positioned in one of three pre-load postures. These postures were: the spine's natural, unloaded curvature (neutral), flexed forward (flexed), and combined flexion and lateral bending (oblique). Deviations from a neutral spine position were shown to significantly increase peak loads and tensile stiffness. The presence of a flexion pre-load caused statistically significant increases in tensile stiffness, tensile force, and bending moments. The addition of a lateral bending pre-load to an already flexed spine did not significantly alter the tensile response. However, the flexion moment response was significantly affected by the additional postural pre-load. This work indicates that the initial conditions of distraction loading significantly affect lumbar spine load response. Therefore, future testing that seeks to emulate crash dynamics of obliquely seated occupants must account for multi-axis loading.

Comparison of small female occupant model responses with experimental data in a reclined posture

Objective: The objective of the current study was to compare the GHBMC female model responses with in-house sled test data for three small female post mortem human surrogates (PMHS) at 32 km/h and a seatback recline angle of 45 degrees. The kinematics and the seatbelt forces were used to compare the female PMHS and model responses. The study aimed to identify updates that may be needed to the model.Methods: In-house experimental sled test kinematic and seatbelt response data for the small females were obtained. The 5^th female GHBMC was simulated with the same boundary conditions as in the experiments. In addition, using the PMHS computed tomography (CT) and test environment scans, the female model geometry was updated to a subject-specific model for one of the specimens, and the models were simulated to obtain 5^th female and subject-specific model responses. The kinematic response and the seatbelt forces for the two models were compared with the average of the three experimental data.Results: The head, T8 and L4 excursions, head and pelvis accelerations and seatbelt forces for the two female models were compared with the experimental data. The model responses were in agreement with the PMHS; however, the subject-specific model showed a closer agreement with the kinematic response. The subject-specific model did not submarine as in the experiments, whereas the 5^th female model submarined. However, the subject-specific model showed 20% higher seatbelt forces than the PMHS.Conclusion: This study showed that anthropometric differences may significantly alter occupant kinematics in reclined posture and need to be incorporated to investigate kinematics and injury mechanisms. The next step of the study involves incorporating age-specific material changes and investigating the subject-specific injury mechanisms. The results will be useful to develop countermeasures for autonomous vehicles.

Loading rate effect on tradeoff of fractures from pelvis to lumbar spine under axial impact loading

Objectives: The transmission of impact loading from the seat-to-pelvis-to-lumbar spine in a seated occupant in automotive and military events is a mechanism for fractures to these body regions. While postmortem human subject (PMHS) studies have replicated fractures to the pelvis or lumbar spine using isolated/component models, the role of the time factor that manifests as a loading rate issue on injuries has not been fully investigated in literature. The objective of this study was to explore the hypothesis that short duration pulses fracture the pelvis while longer pulses fracture the spine, and intermediate pulses involve both components.Methods: Unembalmed PMHS thoracolumbar spine-pelvis specimens were fixed at the superior end, and a six-axis load cell was attached. The specimens were mounted on a vertical accelerator, and noninjury and injury tests were conducted by applying short, medium, or long pulses with 5, 15, or 35 ms durations, respectively. Peak axial, shear and resultant forces were obtained. Injuries were documented using posttest x-ray and computed tomography images and scaled using the AIS (2015).Results: The mean age, stature, weight, body mass index, and BMD of twelve specimens were 64.8 ± 11.4 years, 1.8 ± 0.01 m, 83 ± 13 kg, 26.7 ± 5.0 kg/m², and 114.5 ± 21.3 mg/cc, respectively. For the short, long, and medium duration pulses, the mean resultant forces were 5.6 ± 0.9 kN, 5.9 ± 0.94 kN, and 5.4 ± 1.8 kN, and time durations were 4.8 ± 0.5 ms, 16.3 ± 7.3 ms, and 34.5 ± 7.5 ms, respectively. For the short pulse, pelvis injuries were more severe in 3 out 4 specimens, for the medium pulse, they were distributed between the pelvis and spine, and for the long pulse, spine injuries were more severe in 3 out of 4 specimens.Conclusions: While acknowledging the limitations of the sample size, the results of this study support the hypothesis of the time variable in the tradeoff between pelvis and spine injuries with pulse duration. The tradeoff pattern is attributed to mass recruitment: short pulse biases injuries to pelvis while limiting spinal injuries, and the opposite is true for the longer pulse, thus supporting the hypothesis. It is important to account for the time variable in injury analysis.

Quantifying the Effect of Pelvis Fracture on Lumbar Spine Compression during High-rate Vertical Loading

Fracture to the lumbo-pelvis region is prevalent in warfighters seated in military vehicles exposed to under-body blast (UBB). Previous high-rate vertical loading experimentation using whole body post-mortem human surrogates (PMHS) indicated that pelvis fracture tends to occur earlier in events and under higher magnitude seat input conditions compared to lumbar spine fracture. The current study hypothesizes that fracture of the pelvis under high-rate vertical loading reduces load transfer to the lumbar spine, thus reducing the potential for spine fracture. PMHS lumbo-pelvis components (L4-pelvis) were tested under high-rate vertical loading and force and acceleration metrics were measured both inferior-to and superior-to the specimen. The ratio of inferior-tosuperior responses was significantly reduced by unstable pelvis fracture for all metrics and a trend of reduced ratio was observed with increased pelvis AIS severity. This study has established that pelvis fracture reduces compression forces at the lumbar spine during high-rate vertical loading, thus reducing the potential for fracture to the lumbar spine. Therefore, pelvis injury potential should be considered when implementing lumbar injury criteria specific to UBB.

Importance of neural foraminal narrowing in lumbar spine fractures of low AIS severity

OBJECTIVE

In recent years, based on injuries predicted using machine learning, there have been efforts to reduce imaging performed on trauma patients. While useful, such efforts do not incorporate results from studies investigating the pathophysiology of traumatic events. The objective of this study was to identify potentially symptomatic vertebral foramen narrowing in the presence of minor to moderate (AIS ≤ 2 levels of severity) thoracolumbar fractures sustained in motor vehicle crashes (MVCs).

METHODS

Hospital records and images of patients admitted to a Level One trauma center between the years 2014 and 2018 with the diagnosis of thoracolumbar fracture were reviewed. Spinal injuries were scored using the AIS v2015. In addition, the geometry of the neural foramina, particularly the height of the foramina and intervertebral disk at the posterior region, were measured using reconstructed sagittal computed tomography (CT) images. The criteria for foraminal narrowing were associated with <15 mm for the foraminal height and <4 mm for the height of the posterior disk.

RESULTS

24 patients with MVCs associated thoracolumbar fractures, who met both the clinical and imaging criteria for radiculopathy and foraminal narrowing without spinal cord injury, were considered for the present clinical study. 54% of the total lumbar fracture cases reported were rated as AIS 2 injuries. AIS ≥ 3 cases reported 50% narrowing of foramen, which was expected. However, it was surprising to note that the AIS 2 cases also sustained foraminal stenosis, narrowing ranging from 13% to 20%.

CONCLUSIONS

Low severity (AIS ≤ 2) injuries were often found to be associated with foraminal narrowing leading to clinical complaints. While the present clinical study cannot determine if narrowing existed prior to the trauma, they were certainly asymptomatic prior to the trauma. The present findings emphasize the need for detailed imaging in all instances of thoracolumbar trauma, as clinically significant nerve compression may occur even with modest vertebral body injury.

Belt-induced abdominal injuries in recent frontal impact CIREN cases

OBJECTIVE

The objective is to report sex-related variation in 3-point belt-related abdominal injuries in Crash Injury Research Engineering Network (CIREN) cases.

METHODS

A query of CIREN cases was made for those with the highest ranked Collision Deformation Classification (CDC) to the front plane, a principal direction of force (PDOF) ±20° from 0°, and Abbreviated Injury Scale (AIS) 2+ abdomen injuries attributed to the seat belt. Patterns of injury were categorized as above the crest of the ilium, injuries below the crest of the ilium, and injuries above and below the ilium. This was done in the context of autonomous vehicle occupant kinematics testing results. Twelve 5th and 95th percentile 3-point belt-restrained postmortem human subjects were subjects; test speeds and recline angles varied. Abdomen injuries were anticipated; none were observed.

RESULTS

Thirty-five occupants with belt-related abdominal injuries were identified. Seventeen case occupants sustained an injury only within the pelvic contents: 5 women and 12 men. Nine of the 17 were at or above the 81st percentile for height, 13 were between the 62nd and 80th percentile for height, and 4 were less than the 50th percentile for height.

CONCLUSIONS

The stature component of the body mass index (BMI) appears to be a plausible candidate for an independent variable that is a contributing factor explaining the incidence of pelvic contents injuries when a 3-point belt-restrained occupant is involved in a frontal impact.

Delta-v slope as an indicator of injury

OBJECTIVE

This study's objective was to examine a crash severity characteristic and the relationship as an indicator of abdominal injury causation.

METHODS

Data were analyzed from 23 CIREN case vehicles involved in a frontal type collision, had an AIS 2+ abdominal injury, and contained an electronic data recorder (EDR) download. Data was downloaded from the NHTSA and IIHS crash test databases for comparison. Data was run through a MATLAB algorithm calculating the maximum velocity-time profile slope. This data was compared to the available crash tests.

RESULTS

The CIREN vehicle EDR velocity-time slopes ranged from 233 m/s² to 434 m/s² for crashes with a delta-v range of 42 km/h to 77 km/h. NHTSA NCAP comparable data was available for all cases, and the slopes ranged from 263 m/s² to 405 m/s² calculated from the collected accelerometer. Three comparable tests were available from the IIHS database and the calculated slopes ranged from 252 m/s² to 298 m/s². Four test vehicles had EDR data, two each from NHTSA and IIHS and slopes ranged from 245 m/s² to 281 m/s². The crash test EDRs slope calculations were lower than the accelerometer data. Nine of the 12 case vehicles had slope values lower than the comparable NCAP accelerometer velocity-time slopes.

CONCLUSIONS

Vehicle velocity-time profile can be beneficial to examine the characteristics of crash severity and potential injury. This small sample of field crashes did not indicate a clear relationship of abdominal injury related to crash severity measured by the EDR delta-v slope. EDR results can be considered when determining crash severity, but the limitations need to be understood.

A novel posture control device to induce high-rate complex loads for spine biomechanical studies

Modern environmental scenarios such as autonomous vehicles, aircrafts, and military vehicles position the human body in a nonstandard posture and induce multiplanar loads; however, current spine alignment methods and loading are based on sagittal and planar loads. The objective of this study is to develop a posture control device and demonstrate its ability to induce multiplanar loads to the human cadaver spinal columns. The inferior end of the device was designed to allow a full six degree-of-freedom control for positioning the specimen via a coupled x-y cross table, vertical lift platform, and triaxial rotation mechanism. The superior end of the device was designed such that the cranial fixation of the specimen could be attached to the piston of the electrohydraulic testing apparatus directly or via a rotary disc through a slider-crank mechanism. The former attachment induces complex forces and moments, while the latter induces controlled moments with minimal forces. The usability of the posture control device was demonstrated by conducting experiments with a thoracolumbar spinal column for combined forces and moments, and with a head-neck column for complex moments, and in both cases, the uniaxial travel of the piston was at a dynamic rate. The posture control device can be used to study the biomechanics of the spine under complex loads and with different postures and develop injury criteria for different field environments.

Intervertebral foramen narrowing during vertical dynamic loading

OBJECTIVE

The goal of the present study was to examine the effect of vertebral body fracture on the InterVertebral Foraminal IVF parameters with an input acceleration to the seat bottom in the inferior-to-superior direction.

METHODS

A series of 43 isolated lumbar spines underwent vertical dynamic loading using the vertical accelerative device to determine the influence of inferior to superior loading through the lumbar spine on the intervertebral foramen (IVF) geometries. Existence of foraminal stenosis was quantified using pre- and post-test computed tomography (CT) images. Foraminal height (IVF_Ht) and posterior disk height (PD_Ht) were the key IVF parameters.

RESULTS

There was a significant (p < 0.05) decrease in the post-test IVF measurements compared to the pretest measurements. Furthermore, 30% of the total 49 AIS 2 cases and 70% of the total 21 AIS 3 cases had IVF values below the literature reported thresholds for IVF_Ht of < 15 mm and PD_Ht of < 4 mm, indicating likely occurrence of foraminal stenosis.

CONCLUSIONS

These results underscore the need to assess foraminal geometry in compression fractures of the lumbar spine from vertical dynamic loading.

Human Pelvis Bayesian Injury Probability Curves From Whole Body Lateral Impact Experiments

Injury criteria are used in military, automotive, and aviation environments to advance human safety. While injury risk curves (IRCs) for the human pelvis are published under vertical loading, there is a paucity of analysis that describe IRCs under lateral impact. The objective of the present study is to derive IRCs under this mode. Published data were used from 60 whole-body postmortem human surrogate (PMHS) tests that used repeated testing protocols. In the first analysis, from single impact tests, all injury data points were considered as left censored and noninjury points were considered as right censored, while repeated testing results were treated as interval censored data. In the second analysis, injury data were treated uncensored. Peak force was used as the response variable. Age, total body mass, gender, and body mass index (BMI) were used as covariates in different combinations. Bayesian survival analysis model was used to derive the IRCs. Plus-minus 95% credible intervals (CI) and their normalized CI sizes (NCIS) were obtained. This is the first study to develop IRCs in whole body PMHS tests to describe the human pelvic tolerance under lateral impact using Bayesian models.

AIS scores in spine and spinal cord trauma: Epidemiological considerations

BACKGROUND

The Abbreviated Injury Scale (AIS) is an internationally accepted coding system created by the Association for the Advancement of Automotive Medicine, utilized to code traumatic injuries as a function of severity, the latter often defined as mortality risk. Periodic reassessment of that risk is prudent, in light of advances in health care and relationship of nonanatomic factors to death.

OBJECTIVE

The objective of this study was to reevaluate the risk of death associated with spine fractures with and without neurologic deficit, age factors associated with it, and the impact of hospital coding on the accuracy of these efforts.

METHODS

Medical records and imaging of patients treated at a level 1 trauma center from 2014 through 2016 with discharge International Classification of Diseases, 10th revision (ICD-10) diagnoses of spinal trauma and spinal cord injury (SCI) were reviewed. Data were collected on demographics, complications, neurologic status, and outcomes.

RESULTS

Three hundred seventy patients met the criteria for inclusion in this effort. Errors in ICD-10 discharge codes were seen in 45% of the cases, both false positive and negative. One hundred thirty-four patients, with a mean age of 45, were admitted with neurologic deficit. There were 8 SCI-related deaths; 2 were postoperative out of 110 undergoing surgical treatment. All deaths in this group were in patients with upper level SCI, with a mean age of 68. Ten patients had spontaneous neurologic improvement within 24 h. One hundred nineteen patients without deficit had AIS 2 scored fractures; there was one postoperative death out of 47 patients undergoing surgical treatment. One hundred seventeen patients without deficit suffered AIS 3 fractures; 66 underwent surgery without any deaths. There was one nonoperative death. Age and high quadriplegia were the only factors associated with mortality.

CONCLUSIONS

Mortality risk in patients with deficit was associated more with age at injury than extent of anatomic injury. Spine trauma without neurologic deficit is benign in younger populations and AIS scores could be age adjusted. Mortality risk is higher in high cervical injuries with neurologic deficit and in the elderly. An incidental finding is that demographic studies based solely on discharge ICD coding may contain errors and should be considered critically.

Normalized frontal impact biofidelity kinematic corridors using post mortem human surrogates

Due to reducing cost and powerful computing resources and the ability of finite element human body models (FEHBM) to predict human body response more realistically, they are gaining acceptance to be a substitute for mechanical surrogates. Unlike mechanical surrogates, FEHBM can realistically simulate human kinematics and kinetics. Moreover, an array of quantities can be directly measured from FEHBMs. However, similar to Anthropomorphic Test Devices (ATDs), in order to evaluate the biofidelity, these models must be validated using PMHS response corridors. Therefore, availability of such PMHS corridors that can be used to validate both ATD and FEHBM kinematics is of primary importance. The current study presents normalized biofidelity corridors of head CG, T1, T12, and sacrum accelerations using PMHS frontal sled tests that were previously conducted. In addition, rotational accelerations and displacements of the head are also presented. The experimental data were collected using four specimens. Each specimens were tested with non-injurious pulses using two different velocities (low: 3.6m/s and medium: 6.9m/s). These data were normalized using mass-based technique to represent mid-sized United States population. Using the normalized data, average and plus/minus one standard deviation response corridors were generated that can be used to evaluate the biofidelity of ATDs and FEHBMs.

Human Foot-Ankle Injuries and Associated Risk Curves from Under Body Blast Loading Conditions

Under body blast (UBB) loading to military transport vehicles is known to cause foot-ankle fractures to occupants due to energy transfer from the vehicle floor to the feet of the soldier. The soldier posture, the proximity of the event with respect to the soldier, the personal protective equipment (PPE) and age/sex of the soldier are some variables that can influence injury severity and injury patterns. Recently conducted experiments to simulate the loading environment to the human foot/ankle in UBB events (~5ms rise time) with variables such as posture, age and PPE were used for the current study. The objective of this study was to determine statistically if these variables affected the primary injury predictors, and develop injury risk curves. Fifty belowknee post mortem human surrogate (PMHS) legs were used for statistical analysis. Injuries to specimens involved isolated and multiple fractures of varying severity. The Sanders classification was used to grade calcaneus severity and the AO/OTA classification for distal tibia fracture. Injury risk curves were developed using survival regression analysis and covariates were included whenever statistically significant (p<0.05). With peak force as the injury predictor and age and boot as covariates, the model was statistically significant. However, boot use changed the pattern of injury from predominately calcaneus to predominantly tibia. Also, a severity based risk curve showed tolerance differences between calcaneus (minor/major) and tibia (severity-I/ severity- II) injuries. The tibia demonstrated higher tolerance as compared to either minor or major calcaneus injury. These findings can play a vital role in development of safety systems to mitigate injuries to the occupant.

Male and female WorldSID and post mortem human subject responses in full-scale vehicle tests

OBJECTIVE

This study compares the responses of male and female WorldSID dummies with post mortem human subject (PMHS) responses in full-scale vehicle tests.

METHODS

Tests were conducted according to the FMVSS-214 protocols and using the U.S. Side Impact New Car Assessment Program change in velocity to match PMHS experiments, published earlier. Moving deformable barrier (MDB) tests were conducted with the male and female surrogates in the left front and left rear seats. Pole tests were performed with the male surrogate in the left front seat. Three-point belt restraints were used. Sedan-type vehicles were used from the same manufacturer with side airbags. The PMHS head was instrumented with a pyramid-shaped nine-axis accelerometer package, with angular velocity transducers on the head. Accelerometers and angular velocity transducers were secured to T1, T6, and T12 spinous processes and sacrum. Three chest bands were secured around the upper, middle, and lower thoraces. Dummy instrumentation included five infrared telescoping rods for assessment of chest compression (IR-TRACC) and a chest band at the first abdomen rib, head angular velocity transducer, and head, T1, T4, T12, and pelvis accelerometers.

RESULTS

Morphological responses of the kinematics of the head, thoracic spine, and pelvis matched in both surrogates for each pair. The peak magnitudes of the torso accelerations were lower for the dummy than for the biological surrogate. The brain rotational injury criterion (BrIC) response was the highest in the male dummy for the MDB test and PMHS. The probability of AIS3+ injuries, based on the head injury criterion, ranged from 3% to 13% for the PMHS and from 3% to 21% for the dummy from all tests. The BrIC-based metrics ranged from 0 to 21% for the biological and 0 to 48% for the dummy surrogates. The deflection profiles from the IR-TRACC sensors were unimodal. The maximum deflections from the chest band placed on the first abdominal rib were 31.7 mm and 25.4 mm for the male and female dummies in the MDB test, and 37.4 mm for the male dummy in the pole test. The maximum deflections computed from the chest band contours at a gauge equivalent to the IR-TRACC location were 25.9 mm and 14.8 mm for the male and female dummies in the MDB test, and 37.4 mm for the male dummy in the pole test. Other data (static vehicle deformation profiles, accelerations histories of different body regions, and chest band contours for the dummy and PMHS) are given in the appendix.

CONCLUSIONS

This is the first study to compare the responses of PMHS and male and female dummies in MDB and pole tests, done using the same recent model year vehicles with side airbag and head curtain restraints. The differences between the dummy and PMHS torso accelerations suggest the need for design improvements in the WorldSID dummy. The translation-based metrics suggest low probability of head injury. As the dummy internal sensor underrecorded the peak deflection, multipoint displacement measures are therefore needed for a more accurate quantification of deflection to improve the safety assessment of occupants.

Changing threshold for AIS scores of thoracolumbar compression fractures

BACKGROUND

The Abbreviated Injury Scale (AIS) is an anatomical-based coding system created by the Association for the Advancement of Automotive Medicine, utilized to classify and code injuries resulting from trauma, in order of severity. According to the latest version, all Thoraco-Lumbar Compression Fractures (TLCF), even without injury to other spine components and with >20% loss of height, were branded AIS 3 injuries, reflecting a serious threat to life or permanent disability. Advances in spine imaging, recent biomechanical studies, and long-term outcomes research offer the opportunity to consider these injuries differently.

OBJECTIVE

To re-evaluate the percent compression threshold of TLCF of the spine from motor vehicle crashes (MVC) for serious risk to life identified as surgical treatment, delineating a reliable cut-off for fracture severity and morbidity. Little national data considers degree of compression and provides adequate followup imaging to determine degree of compression, justifying this effort.

METHODS

Charts and radiographs of patients admitted to our institution due to vehicle crashes with isolated (vertebral body only) TLCF between 2008 and 2015 were reviewed. Data were collected on degree of compression, treatment, and long-term outcomes to determine the threshold of permanent injury. Vertebral bodies at the level of fracture were measured both anteriorly and posteriorly, and compared to adjacent segments; percentage compression was calculated.

RESULTS

1470 patient records with diagnoses of spine trauma were reviewed; 695 isolated compression fractures were identified, of which 194 were in vehicle crashes and had adequate imaging and follow-up. Ages ranged from 19 to 82, with a male: female ratio of 60:40. No patient with vertebral body compression of less than 30% underwent surgery unless presenting with a neurological deficit. All 22 surgical patients demonstrated significant retropulsion of bone into the spinal canal. Five surgical patients suffered eight complications; there were no adverse outcomes in the nonsurgical group.

CONCLUSIONS

These results are consistent with evolving clinical thinking, resulting in decreasing surgical incidence and orthosis use. Our data strongly suggests that isolated compression fractures in the absence of neurologic deficit or severe cord compression due to retropulsed bone are self-limiting. Therefore, the AIS scores for these common injuries could be reconsidered and reflect their relatively benign outlook.

Injuries to Post Mortem Human Surrogates in Oblique Aircraft Seat Environment

Increased interest in the airline industry to enhance occupant comfort and maximize seating density has prompted the design and installation of obliquely mounted seats in aircraft. The potential for injury and their mechanism in this seating environment is unknown. Epidemiology-based field injury data do not exist for airplane crashes, however, typical impact scenarios have been determined and safety standards addressing fore, aft, and side-facing seats have been levied by the FAA. The impact scenarios defined in these standards can be used to study likely injuries and injury mechanisms using Post Mortem Human Surrogates (PMHS) in a controlled laboratory environment. Four PMHS were seated upright with Frankfurt plane horizontal in a custom designed seat configured to simulate potential aircraft environments and candidate restraint geometries. A scaled Part 25.562 Emergency Landing condition for horizontal impact was used as the dynamic test input. High speed video recorded occupant kinematics. Pre and posttest x-rays and CT’s were obtained and autopsies were conducted. Severe injuries to the cervical, thoracic, and lumbar spine were observed in three of the four specimens and attributed to torso flail. Pelvis injuries likely caused by the seat belt were found in two tests. Multiple rib fractures were also seen, caused by contact with arm rest or other body regions. The fourth test was run at a lower severity and did not produce injury. This suggests a conservative threshold for human tolerance to this loading environment. Although the study is of a limited sample size, it suggests the need for further testing to develop standards that provide similar levels of safety for obliquely mounted seats as forward/aft facing seats in aircraft.

Injuries in Full-Scale Vehicle Side Impact Moving Deformable Barrier and Pole Tests Using Postmortem Human Subjects

OBJECTIVE

To conduct near-side moving deformable barrier (MDB) and pole tests with postmortem human subjects (PMHS) in full-scale modern vehicles, document and score injuries, and examine the potential for angled chest loading in these tests to serve as a data set for dummy biofidelity evaluations and computational modeling.

METHODS

Two PMHS (outboard left front and rear seat occupants) for MDB and one PMHS (outboard left front seat occupant) for pole tests were used. Both tests used sedan-type vehicles from same manufacturer with side airbags. Pretest x-ray and computed tomography (CT) images were obtained. Three-point belt-restrained surrogates were positioned in respective outboard seats. Accelerometers were secured to T1, T6, and T12 spines; sternum and pelvis; seat tracks; floor; center of gravity; and MDB. Load cells were used on the pole. Biomechanical data were gathered at 20 kHz. Outboard and inboard high-speed cameras were used for kinematics. X-rays and CT images were taken and autopsy was done following the test. The Abbreviated Injury Scale (AIS) 2005 scoring scheme was used to score injuries.

RESULTS

MDB test: male (front seat) and female (rear seat) PMHS occupant demographics: 52 and 57 years, 177 and 166 cm stature, 78 and 65 kg total body mass. Demographics of the PMHS occupant in the pole test: male, 26 years, 179 cm stature, and 84 kg total body mass. Front seat PMHS in MDB test: 6 near-side rib fractures (AIS = 3): 160-265 mm vertically from suprasternal notch and 40-80 mm circumferentially from center of sternum. Left rear seat PMHS responded with multiple bilateral rib fractures: 9 on the near side and 5 on the contralateral side (AIS = 3). One rib fractured twice. On the near and contralateral sides, fractures were 30-210 and 20-105 mm vertically from the suprasternal notch and 90-200 and 55-135 mm circumferentially from the center of sternum. A fracture of the left intertrochanteric crest occurred (AIS = 3). Pole test PMHS had one near-side third rib fracture. Thoracic accelerations of the 2 occupants were different in the MDB test. Though both occupants sustained positive and negative x-accelerations to the sternum, peak magnitudes and relative changes were greater for the rear than the front seat occupant. Magnitudes of the thoracic and sternum accelerations were lower in the pole test.

CONCLUSIONS

This is the first study to use PMHS occupants in MDB and pole tests in the same recent model year vehicles with side airbag and head curtain restraints. Injuries to the unilateral thorax for the front seat PMHS in contrast to the bilateral thorax and hip for the rear seat occupant in the MDB test indicate the effects of impact on the seating location and restraint system. Posterolateral locations of fractures to the front seat PMHS are attributed to constrained kinematics of occupant interaction with torso side airbag restraint system. Angled loading to the rear seat occupant from coupled sagittal and coronal accelerations of the sternum representing anterior thorax loading contributed to bilateral fractures. Inward bending initiated by the distal femur complex resulting in adduction of ipsilateral lower extremity resulted in intertrochanteric fracture to the rear seat occupant. These results serve as a data set for evaluating the biofidelity of the WorldSID and federalized side impact dummies and assist in validating human body computational models, which are increasingly used in crashworthiness studies.

Hybrid III Lower Leg Injury Assessment Reference Curves Under Axial Impacts Using Matched-Pair Tests

The objective of the present study was to derive injury probability curves applicable to the Hybrid III dummy (also termed the Anthropomorphic Test Device, ATD) lower leg under axial impacts for military applications. A matched-pair approach was used. Axial impacts were delivered to below knee foot-ankle complex preparations of the lower leg of the ATD using pendulum and custom vertical accelerator devices. Military boot was used in some tests. Post mortem human surrogate (PMHS) preparations were used as matched-pair tests for injury outcomes. The alignment was such that the foot-ankle complex was orthogonal to the leg (below knee tibia-fibula complex), termed as the normal 90-90 posture. Injury outcomes from the biological surrogate focused on calcaneus and or distal tibia fractures with or without the involvement of articular surfaces. Peak lower tibia load cell forces were obtained from matched-pair dummy tests. Injury and force data were paired, censoring was assigned based on injury outcomes and survival analysis was done using the Weibull distribution to derive dummy-based probability curves. Mean peak forces were extracted at 5, 10, 20 and 50% probability levels. Normalized confidence interval sizes (NCIS) at ± 95% level were computed to determine the tightness-of-fit of the confidence bands. The NCIS data ranged from 0.34 to 0.78 and a peak force of 8.2 kN was associated at the ten percent injury probability level. Other data and curves are given in the body of the paper. The present Injury Assessment Reference Curves and Values (IARC and IARV) may be used in future tests for advancing safety in military environments. These survival analysis processes and IARC and IARV data may also be used in other applications.

Biomechanics of foot/ankle trauma with variable energy impacts

A total of 60 pendulum impacts to the plantar surface of 15 lower limb PMHS specimens were conducted. Impact conditions were chosen to obtain data from high velocity tests without injury. For 19 impacts the specimen was initially positioned in 20-deg of dorsiflexion. The remaining impacts used neutral positioning. The foot-ankle response was investigated based on impact energy and velocity. Response was characterized by heel pad and joint stiffness. For neutral tests, axial force vs compression corridors were developed for 2-3 m/s, 4-6 m/s, and 7-63 J impacts. For dorsiflexion tests corridors of 1-3 m/s, 6-8 m/s, 7-20 J, and 80-100 J were developed. These results indicate foot/ankle response is not more sensitive to impact energy than velocity. Injury risk curves were developed for both neutral and dorsiflexion positioning using logistic regression. Strain gage data were used to obtain uncensored force values for injury analysis. In neutral, 50% probability of injury occurred at 6800 N. In dorsiflexion, 50% probability occurred at 7900 N, but the regression was not statistically significant. These preliminary results indicate dorsiflexed specimens fracture at a higher force than neutral specimens.

A computational study of injury severity and pattern sustained by overweight drivers in frontal motor vehicle crashes

The objective of this study was to examine the role of body mass and subcutaneous fat in injury severity and pattern sustained by overweight drivers. Finite element models were created to represent the geometry and properties of subcutaneous adipose tissue in the torso with data obtained from reconstructed magnetic resonance imaging data-sets. The torso adipose tissue models were then integrated into the standard multibody dummy models together with increased inertial parameters and sizes of the limbs to represent overweight occupants. Frontal crash simulations were carried out considering a variety of occupant restraint systems and regional body injuries were measured. The results revealed that differences in body mass and fat distribution have an impact on injury severity and pattern. Even though the torso adipose tissue of overweight subjects contributed to reduce abdominal injury, the momentum effect of a greater body mass of overweight subjects was more dominant over the cushion effect of the adipose tissue, increasing risk of other regional body injuries except abdomen. Through statistical analysis of the results, strong correlations (p < 0.01) were found between body mass index and regional body injuries except neck injury. The analysis also revealed that a greater momentum of overweight males leads to greater forward torso and pelvic excursions that account for higher risks (p < 0.001) of head, thorax and lower extremity injury than observed in non-overweight males. The findings have important implications for improving the vehicle and occupant safety systems designed for the increasing global obese population.

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.

Obesity and non-fatal motor vehicle crash injuries: sex difference effects

Background

Obesity and motor vehicle crash (MVC) injuries are two parallel epidemics in the United States. An important unanswered question is if there are sex differences in the associations between the presence of obesity and non-fatal MVC injuries.

Objectives

To further understand the association between obesity and non-fatal motor vehicle crash injuries, particularly the sex differences in these relations.

Methods

We examined this question by analyzing data from the 2003 to 2007 National Automotive Sampling System Crashworthiness Data System (NASS CDS). A total of 10, 962 drivers who were aged 18 years or older and who survived frontal collision crashes were eligible for study.

Results

Male drivers experienced a lower rate of overall non-fatal MVC injuries than did female drivers (38.1% vs. 52.2%) but a higher rate of severe injuries (0.7% vs. 0.2%). After adjusting for change in velocity (ΔV) during the crashes, obese male drivers showed a much higher risk [logistic coefficients of BMI for moderate, serious, and severe injury are 0.0766, 0.1470, and 0.1792, respectively; all p<0.05] of non-fatal injuries than did non-obese male drivers and these risks increased with injury severity. Non-fatal injury risks were not found to be increased in obese female drivers. The association between obesity and risk of non-fatal injury was much stronger for male drivers than for female drivers.

Conclusion

The higher risk of non-fatal MVC injuries in obese male drivers might result from their different body shape and fat distribution compared with obese female drivers. Our findings should be considered for obesity reduction, traffic safety evaluation and vehicle design for obese male drivers and provide testable hypotheses for future studies.

BMI and risk of serious upper body injury following motor vehicle crashes: concordance of real-world and computer-simulated observations

BACKGROUND

Men tend to have more upper body mass and fat than women, a physical characteristic that may predispose them to severe motor vehicle crash (MVC) injuries, particularly in certain body regions. This study examined MVC-related regional body injury and its association with the presence of driver obesity using both real-world data and computer crash simulation.

METHODS AND FINDINGS

Real-world data were from the 2001 to 2005 National Automotive Sampling System Crashworthiness Data System. A total of 10,941 drivers who were aged 18 years or older involved in frontal collision crashes were eligible for the study. Sex-specific logistic regression models were developed to analyze the associations between MVC injury and the presence of driver obesity. In order to confirm the findings from real-world data, computer models of obese subjects were constructed and crash simulations were performed. According to real-world data, obese men had a substantially higher risk of injury, especially serious injury, to the upper body regions including head, face, thorax, and spine than normal weight men (all p<0.05). A U-shaped relation was found between body mass index (BMI) and serious injury in the abdominal region for both men and women (p<0.05 for both BMI and BMI(2)). In the high-BMI range, men were more likely to be seriously injured than were women for all body regions except the extremities and abdominal region (all p<0.05 for interaction between BMI and sex). The findings from the computer simulation were generally consistent with the real-world results in the present study.

CONCLUSIONS

Obese men endured a much higher risk of injury to upper body regions during MVCs. This higher risk may be attributed to differences in body shape, fat distribution, and center of gravity between obese and normal-weight subjects, and between men and women. Please see later in the article for the Editors' Summary.

Importance of physical properties of the human head on head-neck injury metrics

OBJECTIVES

To demonstrate the importance of using specimen-specific head physical properties in head-neck dynamics.

METHODS

Eight postmortem human subjects were subjected to side impact. A 9-axis accelerometer package was used to obtain head translational accelerations. After test, the head was isolated at the skull base, circumference, breadth, and length were obtained, and mass, center of gravity, and occipital condylar locations and moments of inertia were determined. Using specimen-specific and gathered accelerations, 3-dimensional head center of gravity accelerations and forces and moments at the occipital condyles were computed. Head physical properties were also extracted from regression equations using external dimensions of each subject. Using these properties and gathered kinematics, above-described accelerations and forces and moments were computed and compared with specimen-specific results.

RESULTS

Head masses predicted by stature and total body mass were more in close agreement with specimen-specific data than head masses predicted by head circumference or head circumference and head length. The center of gravity to the occipital condyle vector was shorter in the literature-based dataset than the actual specimen-specific vector. Differences in moments of inertias between predicted and specimen-specific data ranged from -15 to 59 percent. Variations in peak antero-posterior shear, lateral shear, and axial force ranged from -12 to 46 percent, -21 to 78 percent, and -17 to 50 percent. Differences in peak lateral moment, sagittal moment, and axial torque ranged from -45 to 78 percent, -86 to 327 percent, and -96 to 112 percent. These were normalized using specimen-specific data.

CONCLUSIONS

Considerable variations in physical properties and injury metrics between data obtained from literature-based regression equations and actual data for each specimen suggest the critical importance of specimen-specific data to accurately describe the biodynamic response and establish tolerance criteria. Because neck dynamics control head kinematics (and vice versa), these results emphasize the need to determine physical properties of each specimen following impact tests.

The continued burden of spine fractures after motor vehicle crashes

OBJECT

Spine fractures are a significant cause of morbidity and mortality after motor vehicle crashes (MVCs). Public health interventions, such as the National Highway Traffic Safety Administration's Federal Motor Vehicle Safety Standards, have led to an increase in automobiles with air bags and the increased use of seat belts to lessen injuries sustained from MVCs. The purpose of this study was to evaluate secular trends in the occurrence of spine fractures associated with MVCs and evaluate the association between air bag and seat belt use with spine fractures.

METHODS

Using the Crash Outcome Data Evaluation System, a database of the police reports of all MVCs in Wisconsin linked to hospital records, the authors studied the occurrence of spine fractures and seat belt and air bag use from 1994 to 2002. Demographic information and crash characteristics were obtained from the police reports. Injury characteristics were determined using International Classification of Disease, 9th Revision, Clinical Modification (ICD-9-CM) hospital discharge codes.

RESULTS

From 1994 to 2002, there were 29,860 hospital admissions associated with automobile or truck crashes. There were 20,276 drivers or front-seat passengers 16 years of age and older who were not missing ICD-9-CM discharge codes, seat belt or air bag data, and who had not been ejected from the vehicle. Of these, 2530 (12.5%) sustained a spine fracture. The occurrence of spine fractures increased over the study period, and the use of a seat belt plus air bag, and of air bags alone also increased during this period. However, the occurrence of severe spine fractures (Abbreviated Injury Scale Score > or =3) did not significantly increase over the study period. The use of both seat belt and air bag was associated with decreased odds of a spine fracture. Use of an air bag alone was associated with increased odds of a severe thoracic, but not cervical spine fracture.

CONCLUSIONS

Among drivers and front-seat passengers admitted to the hospital after MVCs, the occurrence of spine fractures increased from 1994 to 2002 despite concomitant increases in seat belt and air bag use. However, the occurrence of severe spine fractures did not increase over the study period. The use of both seat belt and air bag is protective against spine fractures. Although the overall increased occurrence of spine fractures may appear contrary to the increased use of seat belts and air bags in general, it is possible that improved imaging technology may be associated with an increase in the diagnosis of relatively minor fractures. However, given the significant protective effects of both seat belt and air bag use against spine fractures, resources should continue to be dedicated toward increasing their use to mitigate the effects of MVCs.

Head motions using nine accelerometer package and angular rate sensors

This study compared linear and angular accelerations and angular velocities of the head using two systems. The first sensor was a custom-developed pyramid nine accelerometer package (PNAP) in 3-2-2-2 configuration. The three corners of the base contained two biaxial accelerometers in the 2-2-2 array, and the vertex contained the tri-axial accelerometer. The second sensor was a recently available angular rate sensor. Both sensors were mounted on the periphery of the head of an intact post mortem human cadaver specimen (PMHS), exposed to impact loading. Using the dynamic equations of equilibrium and geometric properties of the head of the PMHS, linear location-specific acceleration data from the PNAP device were transformed to head angular accelerations and velocities and linear accelerations at its center of gravity. Using recorded angular velocity data from the rate sensor, angular and linear accelerations were obtained. A comparative evaluation of these data indicated that the angular rate sensor is preferable for rotational velocities and the PNAP device for angular accelerations. A combination of angular velocity data from the rate sensor and angular acceleration data from the PNAP device produced the most preferable temporal linear acceleration data at the center of gravity of the head. It may be prudent to use both sensors to obtain linear and angular acceleration and rotational velocity data from impact tests.

Regional brain strains and role of falx in lateral impact-induced head rotational acceleration

The objective of the present investigation is to determine localized brains strains in lateral impact using finite element modeling and evaluate the role of the falx. A two-dimensional finite element model was developed and validated with experimental data from literature. Motions and strains from the stress analysis matched well with experimental results. A parametric study was conducted by introducing flexible falx in the finite element model. For the model with the rigid falx, high strains were concentrated in the corpus callosum, whereas for the model with the flexible falx, high strains extended into the cerebral vertex. These preliminary findings indicate that the flexibility of falx has an effect on regional brain strains in lateral impact.

Obesity and risk for death due to motor vehicle crashes

OBJECTIVES

We examined the role of body mass index (BMI) and other factors in driver deaths within 30 days after motor vehicle crashes.

METHODS

We collected data for 22 107 drivers aged 16 years and older who were involved in motor vehicle crashes from the Crashworthiness Data System of the National Automotive Sampling System (1997-2001). We used logistic regression and adjusted for confounding factors to analyze associations between BMI and driver fatality and the associations between BMI and gender, age, seatbelt use, type of collision, airbag deployment, and change in velocity during a crash.

RESULTS

The fatality rate was 0.87% (95% confidence interval [CI]=0.50, 1.24) among men and 0.43% (95% CI=0.31, 0.56) among women involved as drivers in motor vehicle crashes. Risk for death increased significantly at both ends of the BMI continuum among men but not among women (P<.05). The association between BMI and male fatality increased significantly with a change in velocity and was modified by the type of collision, but it did not differ by age, seatbelt use, or airbag deployment.

CONCLUSIONS

The increased risk for death due to motor vehicle crashes among obese men may have important implications for traffic safety and motor vehicle design.

Force and acceleration corridors from lateral head impact

This study was conducted to provide force and acceleration corridors at different velocities describing the dynamic biomechanics of the lateral region of the human head. Temporo-parietal impact tests were conducted using specimens from ten unembalmed post-mortem human subjects. The specimens were isolated at the occipital condyle level, and pre-test x-ray and computed tomography images were obtained. They were prepared with multiple triaxial accelerometers and subjected to increasing velocities (up to 7.7 m/s) using free-fall techniques by impacting onto a force plate from which forces were recorded. A 40-durometer padding (50-mm thickness) material covering the force plate served as the impacting boundary condition. Computed tomography images obtained following the final impact test were used to identify pathology. Four specimens sustained skull fractures. Peak force, displacement, acceleration, energy, and head injury criterion variables were used to describe the dynamic biomechanics. Force and acceleration responses obtained from this experimental study along with other data will be of value in validating finite element models. The study underscored the need to enhance the sample size to derive probability-based human tolerance to side impacts.

A new biomechanically-based criterion for lateral skull fracture

This work develops a skull fracture criterion for lateral impact-induced head injury using postmortem human subject tests, anatomical test device measurements, statistical analyses, and finite element modeling. It is shown that skull fracture correlates with the tensile strain in the compact tables of the cranial bone as calculated by the finite element model and that the Skull Fracture Correlate (SFC), the average acceleration over the HIC time interval, is the best predictor of skull fracture. For 15% or less probability of skull fracture the lateral skull fracture criterion is SFC < 120 g, which is the same as the frontal criterion derived earlier. The biomechanical basis of SFC is established by its correlation with strain.

Injury biomechanics of C2 dens fractures

The objective of this study is to analyze the biomechanics of dens fractures of the second cervical vertebra in the adult population due to motor vehicle crashes. Case-by-case records from the Crash Injury Research and Engineering Network (CIREN) and National Automotive Sampling System (NASS) databases were used. Variables such as change in velocity, impact direction and body habitus were extracted. Results indicated that similarities exist in the two databases despite differences in sampling methods between the two sources (e.g., CIREN is not population based). Trauma is predominantly associated with the frontal mode of impact. Majority of injuries occur with change in velocities below current federal guideline thresholds. No specific bias exists with respect to variables such as age, height, weight, and gender. Because similar conclusions can be drawn with regard to vehicle model years, design changes during these years may have had little effect on this injury. To ameliorate trauma, emphasis should be placed on the frontal impact mode and entire adult population. Because of clinical implications in the fracture type (II being most critical) and lack of specific coding, CIREN data demonstrates the need to improve injury coding in the AIS and application in the NASS to enhance occupant safety and treatment in the field of automotive medicine.

Statistically and biomechanically based criterion for impact-induced skull fracture

This work developed a skull fracture criterion for impact-induced head injury, using post mortem human subject tests, anatomical test device measurements, statistical analyses, and finite element modeling. It is shown that skull fracture correlates with the tensile strain in the outer table of the cranial bone, and an index termed the Skull Fracture Correlate (SFC) predicts injury. SFC offers several advantages as a protection criterion. It accounts for compliance of the impact site; it is extensible to varying head mass; and it is easily implemented using current software. For a 15% or less probability of skull fracture the criterion is SFC < 120 g, with a 95% confidence band of 88 < SFC < 135 g.

Orbital blowout fractures: experimental evidence for the pure hydraulic theory

BACKGROUND

The mechanism of injury and the underlying biomechanics of orbital blowout fractures remain controversial. The "hydraulic" theory proposes that a generalized increased orbital content pressure results in direct compression and fracturing of the thin orbital bone.

OBJECTIVE

To examine the pure hydraulic mechanism of injury by eliminating the factor of globe-to-wall contact and its possible contribution to fracture thresholds and patterns.

MATERIALS AND METHODS

Five fresh human cadaver specimens were used for the study. In each cadaver head, 1 orbit was prepared to mimic the normal physiologic condition by increasing the hypotony of the cadaver globe to normal intraocular pressure (15-20 mm Hg) with intravitreous injection of isotonic sodium chloride solution (saline). The second orbit served as a "hydraulic control," whereby the globe and orbital contents were exenterated and replaced by a saline-filled balloon at physiologic intraocular pressure. A 1-kg pendulum measuring 2.5 cm in diameter was used to strike the cadaver heads. Drop heights ranged from 0.2 m to 1.1 m (1960 mJ to 10 780 mJ energy). Each head was struck twice, once to each orbit. Direct visualization, high-speed videography, and computed tomographic scans were used to determine injury patterns at various heights between the 2 orbits.

RESULTS

A fracture threshold was found at a drop height of 0.3 m (2940 mJ). Fracture severity and displacement increased with incremental increases in drop height (energy). Fracture displacement, with herniation of orbital contents, was obtained at heights above 0.5 m (4900 mJ). Isolated orbital floor fractures were obtained at lower heights, with medial wall fractures occurring in conjunction with floor fractures at higher energies (> or =6860 mJ). The globe intact side and balloon (hydraulic control) side showed nearly identical fracture patterns and levels of displacement at each drop height.

CONCLUSIONS

This study provides support for the "hydraulic" theory and evidence against the role of direct globe-to-wall contact in the pathogenesis of orbital blowout fractures. In addition, the orbital floor was found to have a lower threshold for fracture than the medial wall. Preliminary threshold values for fracture occurrence and soft tissue displacement were obtained.

Experimental trauma to the malar eminence: fracture biomechanics and injury patterns

OBJECTIVES

To document patterns of facial fractures after trauma to the malar eminence and to elucidate biomechanical factors relevant to the injury patterns.

STUDY DESIGN AND SETTING

Studies were conducted on 14 cadaver heads. Study variables included impact velocity, contact area, impact force, and zygomatic skin thickness. Bony fractures and clinical injury patterns were documented. A fracture severity rating scale was devised and statistically correlated to the study variables using regression ANOVA analysis.

RESULTS

A broad spectrum of facial fracture patterns was found. Skin thickness and surface area did not correlate with fracture severity (P = 0.67, P = 0.83, respectively). Impact force demonstrated a trend toward significance (P = 0.14). Velocity was most correlative with fracture severity (P = 0.07). A critical threshold velocity (3.5 m/s) was found to correlate with the most severe fracture patterns.

CONCLUSIONS

A broad spectrum of facial fracture patterns was demonstrated after experimental trauma to the malar eminence. Contact surface area and zygomatic skin thickness were not found to be significant factors in fracture severity. Velocity, rather than impact force, was most correlative with fracture severity. The most severe fracture patterns were elicited by velocities above 3.5 m/s.

Biomechanics of the intact and surgically repaired proximal interphalangeal joint collateral ligaments

Collateral ligament injuries to the proximal interphalangeal joint are common. When the collateral ligament is completely ruptured, surgical repair may be required. The strength of the lateral collateral ligaments of the proximal interphalangeal joint was examined using axial distraction on an electrohydraulic testing apparatus. Eighty-five fresh human adult cadaver fingers were assessed; 38 intact ligaments were first examined. The strength of the native ligament was 162.5 N. Forty-seven ligament repair preparations were tested: suture repair (27.8 N), pull-out wire repair (35.9 N), and repair using a Mitek suture anchor (38.4 N). The breaking strength of the intact ligaments was significantly greater than that of any repair. All repaired ligaments failed at the site of the repair. The ligaments repaired by the pull-out wire and Mitek anchor technique were significantly stronger than those repaired with the suture technique.

Cervical spine injuries from high-velocity forces: a pathoanatomic and radiologic study

The detailed analysis of the radiologic and pathoanatomic data from 10 human cadaver head-neck complexes defined the type and extent of expected cervical spine injuries after high-velocity flexion-compression loads to the cranium. All specimens demonstrated multiple injuries with both contiguous and noncontiguous patterns. Although all preparations showed evidence of axial compression, a multiplicity of other force vectors, including noncontiguous occurrences of flexion, extension, and shear, were documented. These findings indicate that the injury pattern is not a sequential process but a reaction to changes in the segmental interrelations of the various vertebral column components, including varying vector applications of injurious forces at the segmental level. The presence of moderate or severe spondylotic alterations restricted the distal transmission of injury forces with the principal injury patterns occurring at or proximal to the initial level of severe spondylotic involvement. These data emphasize the need for increased awareness of the presence of multiple cervical spine injuries, both contiguous and noncontiguous, and that separate levels of compromise may not share similar mechanisms of injury.

Comparison of nuclear magnetic resonance spectroscopy with dual-photon absorptiometry and dual-energy X-ray absorptiometry in the measurement of thoracic vertebral bone mineral density: compressive force versus bone mineral

31P nuclear magnetic resonance spectroscopy (NMRS) measurements were made on human T2 and T3 vertebral bodies. The bone mineral content (BMC) of isolated vertebral bodies minus the posterior elements and disks was measured using (1) NMRS on a 3.5 T, 85 mm bore GE Medical Systems NT-150 superconducting spectrometer, (2) a Lunar Corporation DPX-L dual-energy X-ray absorptiometry (DXA) scanner in an anterior-posterior (AP) orientation, (3) a Norland Corporation XR26 DXA scanner, also in an AP direction, and (4) a Norland Corporation model 2600 dual-photon absorptiometry (DPA) densitometer in both the AP and superior-inferior (SI) directions. Vertebral body volumes were measured using a water displacement technique to determine volume bone mineral densities (VBMD). They were then compressed to failure using an electrohydraulic testing device, followed by ashing in a muffle furnace at 700 degrees C for 18 h. Correlations of BMC between NMRS and DPA, DXA and ashing were excellent (0.96 < or = r < or = 0.99); in a one-way analysis of variance (ANOVA) test, means were not statistically different at a p level of 0.757. The correlations of VBMD between NMRS and the other methods were not as good (0.83 < or = r < or = 0.95); in a one-way ANOVA test, means were not statistically different at a p level of 0.089. BMC was a better predictor of ultimate compressive failure than VBMD for all six methods. For NMRS, the regression coefficient for BMC was r2 = 0.806, compared with r2 = 0.505 for VBMD. NMRS may prove an alternative to present methods of determining bone mineral.

Effects of anterior vertebral grafting on the traumatized lumbar spine after pedicle screw-plate fixation

This study was conducted to determine the effects of corpectomy and anterior strut grafting on the biomechanics of traumatized lumbar spine after pedicle screw-plate fixation. Eight lumbar spines were loaded until fracture (initial cycle) and then reloaded to the same deformation (injury cycle). After transpedicular fixation, spines were again loaded (fixation cycle). Partial corpectomy of the fractured body and anterior strut grafting were accomplished; the spine reloaded (strut cycle). Spine angles were measured and biomechanical strength and kinematic parameters analyzed. Load-deformation relationships were similar for fixation and strut cycles until maximum load; at failure, loads were higher for the former (P < 0.05), however. Alignment was improved by stabilization or stabilization plus anterior grafting (P < 0.05). Vertebral height was best maintained by grafting as an adjunct to pedicle fixation (P < 0.05). Kinematics were largely unaffected by grafting, except for reduced motion at the posterior vertebral targets between the fixated levels (P < 0.05). The strength of the fixated spine is relatively unchanged by corpectomy and anterior grafting; alignment may be improved in the latter group.

Biomechanical evaluation of Caspar cervical screws: comparative stability under cyclical loading

Anterior cervical instrumentation is used as an adjunct to bone fusion; however, definitive biomechanical data to support some applications and techniques are lacking. In the absence of supportive experimental data, posterior cortical penetration has been recommended with the Caspar system. Previously, we compared the axial pull-out strength of Caspar screws with and without posterior cortical penetration. This study compares the stability of unicortical versus bicortical screw penetration groups under cyclical loading simulating physiological flexion-extension. Caspar screws were placed in human cadaveric vertebrae with or without posterior cortical purchase. Each screw was separately tested, simulating flexion-extension to 200 cycles. Deformation time data allowed a direct comparison of screw "wobble" with and without posterior cortical purchase. The mean deformation differences between subcortical and bicortical groups were statistically significant and increased over time within both groups. Enhanced stability was noted with bicortical purchase throughout most of the examined range, becoming more pronounced over longer periods of cyclical loading. Significant (P < 0.05) increases in deformation over time were noted for both groups, suggesting potentially significant deterioration at the screw-bone interface, despite bicortical purchase. Such deterioration with repeated flexion-extension loading may be of concern in the use of Caspar plates in the presence of multicolumn instability.

Kinematics of the lumbar spine following pedicle screw plate fixation

This investigation was conducted to determine the kinematic response of the lumbar spine instrumented with transpedicular screws and plates. Seven unembalmed human cadaveric lumbar spines were used. Retroreflective targets were inserted into the bony landmarks of each vertebral body, facet column, and spinous process. The specimen was quasistatically loaded until failure (initial cycle) using an electrohydraulic testing device at a rate of 2.5 mm/sec. After radiography, the specimen was again loaded (injury cycle) to the failure compression determined in the previous cycle. Transpedicular screws then were inserted bilaterally at one level proximal and distal to injury. The stabilized cycle of loading was conducted using the procedure adopted in the injury cycle. Comparative analysis of the localized kinematic data between the stabilized and injured columns indicated a reduction in motion between fixated levels, increasing the rigidity of the column. At levels proximal and distal to fixation, however, motion increased, indicating added flexibility. These alterations in the motion, observed during single-cycle loading, may be further accentuated in vivo, leading to hypermobility and degeneration of the spine.