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.

Oswestry Disability Index scores correlate with MRI measurements in degenerating intervertebral discs and endplates.

BACKGROUND: Low back pain (LBP) is a widespread problem and the leading cause of disability worldwide. While the cause of LBP is multifactorial, several studies suggested that inflammatory mediators in damaged subchondral plates of degenerating discs may lead to chemical sensitization and mechanical stimulation, eventually causing pain. The goal of this study was to explore associations between such changes and LBP-related disability using dynamic contrast-enhanced MRI. METHODS: Thirty-two patients diagnosed with nonspecific LBP and 24 healthy control subjects were studied with dynamic contrast-enhanced (DCEMRI) MRI and T1r (spin-lattice relaxation in the rotating frame) acquisitions. DCEMRI enhancement in disc endplate regions and average T1ρ measurements in the nucleus pulposus were extracted. The LBP patients were grouped based on their Oswestry Disability Index (ODI) scores and associations between MRI measurements and ODI scores were analyzed. RESULTS: Significant associations were found between ODI scores and DCEMRI enhancement in the cartilaginous endplate regions of the most degenerated discs. ODI scores also correlated with T1ρ measurements in the nucleus pulposus of degenerating discs. CONCLUSIONS: DCEMRI enhancement in the cartilaginous endplate regions and lower T1ρ measurements in the nucleus pulposus (NP) were associated with greater disability that is related to low back pain as reported on the ODI. This complements earlier reports suggesting a link between LBP and endplate degeneration. Further studies are needed to validate these findings. SIGNIFICANCE: Our findings indicated that dynamic contrast-enhanced MRI signal enhancement in the cartilaginous endplate regions were associated with greater disability related to low back pain. This signal enhancement might be an indication of inflammatory changes in disc endplate regions. Therefore, advanced quantitative imaging techniques like the ones presented in this study might be needed to complement conventional radiological evaluations to identify the subset of patients who could potentially benefit from novel therapies directed towards treating the disc endplate regions.

Biomechanical tolerance of whole lumbar spines in straightened posture subjected to axial acceleration.

Quantification of biomechanical tolerance is necessary for injury prediction and protection of vehicular occupants. This study experimentally quantified lumbar spine axial tolerance during accelerative environments simulating a variety of military and civilian scenarios. Intact human lumbar spines (T12-L5) were dynamically loaded using a custom-built drop tower. Twenty-three specimens were tested at sub-failure and failure levels consisting of peak axial forces between 2.6 and 7.9 kN and corresponding peak accelerations between 7 and 57 g. Military aircraft ejection and helicopter crashes fall within these high axial acceleration ranges. Testing was stopped following injury detection. Both peak force and acceleration were significant (p < 0.0001) injury predictors. Injury probability curves using parametric survival analysis were created for peak acceleration and peak force. Fifty-percent probability of injury (95%CI) for force and acceleration were 4.5 (3.9-5.2 kN), and 16 (13-19 g). A majority of injuries affected the L1 spinal level. Peak axial forces and accelerations were greater for specimens that sustained multiple injuries or injuries at L2-L5 spinal levels. In general, force-based tolerance was consistent with previous shorter-segment lumbar spine testing (3-5 vertebrae), although studies incorporating isolated vertebral bodies reported higher tolerance attributable to a different injury mechanism involving structural failure of the cortical shell. This study identified novel outcomes with regard to injury patterns, wherein more violent exposures produced more injuries in the caudal lumbar spine. This caudal migration was likely attributable to increased injury tolerance at lower lumbar spinal levels and a faster inertial mass recruitment process for high rate load application. Published 2017. This article is a U.S. Government work and is in the public domain in the USA. J Orthop Res 36:1747-1756, 2018.

Cervical spine injuries, mechanisms, stability and AIS scores from vertical loading applied to military environments.

PURPOSE: The purpose of this study was to determine injuries to osteo-ligamentous structures of cervical column, mechanisms, forces, severities and AIS scores from vertical accelerative loading. METHODS: Seven human cadaver head-neck complexes (56.9 ± 9.5 years) were aligned based on seated the posture of military soldiers. Army combat helmets were used. Specimens were attached to a vertical accelerator to apply caudo-cephalad g-forces. They were accelerated with increasing insults. Intermittent palpation and radiography were done. A roof structure mimicking military vehicle interior was introduced after a series of tests and experiments were conducted following similar protocols. Upon injury detection, CT and dissection were done. Temporal force responses were extracted, peak forces and times of occurrence were obtained, injury severities were graded, and spine stability was determined. RESULTS: Injuries occurred in tests only when the roof structure was included. Responses were tri-phasic: initial thrust, secondary tensile, tertiary roof contact phases. Peak forces: 1364-4382 N, initial thrust, 165-169 N, secondary tensile, 868-3368 N tertiary helmet-head roof contact phases. Times of attainments: 5.3-9.6, 31.7-42.6, 55.0-70.8 ms. Injuries included fractures and joint disruptions. Multiple injuries occurred in all but one specimen. A majority of injury severities were AIS = 2. Spines were considered unstable in a majority of cases. CONCLUSIONS: Spine response was tri-phasic. Injuries occurred in roof contact tests with the helmeted head-neck specimen. Multiplicity and unstable nature of AIS = 2 level injuries, albeit at lower severities, might predispose the spine to long-term accelerated degenerative changes. Clinical protocols should include a careful evaluation of sub-catastrophic injuries in military patients.

Lumbar spine endplate fractures: Biomechanical evaluation and clinical considerations through experimental induction of injury.

Lumbar endplate fractures were investigated in different experimental scenarios, however the biomechanical effect of segmental alignment was not outlined. The objectives of this study were to quantify effects of spinal orientation on lumbar spine injuries during single-cycle compressive loads and understand lumbar spine endplate injury tolerance. Twenty lumbar motion segments were compressed to failure. Two methods were used in the preparation of the lumbar motion segments. Group 1 (n = 7) preparation maintained pre-test sagittal lordosis, whereas Group 2 (n = 13) specimens had a free-rotational end condition for the cranial vertebra, allowing sagittal rotation of the cranial vertebra to create parallel endplates. Five Group 1 specimens experienced posterior vertebral body fracture prior to endplate fracture, whereas two sustained endplate fracture only. Group 2 specimens sustained isolated endplate fractures. Group 2 fractures occurred at approximately 41% of the axial force required for Group 1 fracture (p < 0.05). Imaging and specimen dissection indicate endplate injury consistently took place within the confines of the endplate boundaries, away from the vertebral periphery. These findings indicate that spinal alignment during compressive loading influences the resulting injury pattern. This investigation identified the specific mechanical conditions under which an endplate breach will take place. Development of endplate injuries has significant clinical implication as previous research identified internal disc disruption (IDD) and degenerative disc disease (DDD) as long-term consequences of the axial load-shift that occurs following a breach of the endplate. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1084-1091, 2016.

Changes in perfusion and diffusion in the endplate regions of degenerating intervertebral discs: a DCE-MRI study.

PURPOSE: Dynamic contrast-enhanced MRI (DCE-MRI) was used to investigate the associations between intervertebral disc degeneration and changes in perfusion and diffusion in the disc endplates. METHODS: 56 participants underwent MRI scans. Changes in DCE-MRI signal enhancement in the endplate regions were analyzed. Also, a group template was generated for the endplates and enhancement maps were registered to this template for group analysis. RESULTS: DCE-MRI enhancement changed significantly in cranial endplates with increased degeneration. A similar trend was observed for caudal endplates, but it was not significant. Group-averaged enhancement maps revealed major changes in spatial distribution of endplate perfusion and diffusion with increasing disc degeneration especially in peripheral endplate regions. CONCLUSIONS: Increased enhancement in the endplate regions of degenerating discs might be an indication of ongoing damage in these tissues. Therefore, DCE-MRI could aid in understanding the pathophysiology of disc degeneration. Moreover, it could be used in the planning of novel treatments such as stem cell therapy.

Association between intervertebral disc degeneration and endplate perfusion studied by DCE-MRI.

PURPOSE: The goal of this study was to study the association between solute transport mechanisms in cartilaginous disc endplates and the degeneration of intervertebral discs. Intervertebral disc degeneration is a multi-factorial process. It is suspected that poor nutrient delivery to discs might be a factor leading to degeneration. Several studies suggest that defects in disc endplates could lead to poor transport of nutrients. An imaging technique assessing endplate perfusion could be a valuable tool in investigating disc degeneration. There is currently no universally accepted technique assessing endplate perfusion in vivo. METHODS: Nine adult patients exhibiting varying levels of intervertebral disc degeneration were included. MRI was used to study the association between blood perfusion in 90 lumbar disc endplates and disc degeneration in 45 lumbar discs. Solute transport mechanism through endplates was assessed indirectly by dynamic contrast enhanced (DCE) MRI. T2-weighted MRI was used for conventional Pfirrmann classification. RESULTS: A positive association was observed between Pfirrmann grades and endplate DCE-MRI enhancement. A differential enhancement between cranial and caudal endplates was also observed, which increased with Pfirrmann grades. This differential enhancement was also dependent on the lumbar level. CONCLUSIONS: Increased MRI signal enhancement in the cartilaginous endplates of degenerated discs might indicate damage to the subchondral bone of the vertebral bodies. The endplate enhancement characteristic could aid in understanding the pathophysiology of disc degeneration and planning treatment more effectively.

Intervertebral disc height loss demonstrates the threshold of major pathological changes during degeneration.

PURPOSE: Quantitative MRI techniques were utilized to study intervertebral disc degeneration. Main focus was to develop a novel approach to quantify disc height loss associated with disc degeneration. Currently there is no universally accepted metric of degeneration based on measurement of disc height. Such quantitative imaging methods would complement qualitative visual assessment methods currently used and offer a valuable diagnostic tool. METHODS: 51 adult participants took part in this MRI study. T2 weighted images were used to obtain disc height index (DHI) and also a semi-quantitative metric based on relative voxel intensities. For DHI, each disc was given a score based on standard deviations from the mean DHI of healthy discs. Diffusion Weighted MRI was used to assess morphological changes in the nucleus pulposus. Conventional Pfirrmann classification was used as the gold standard to assess these quantitative approaches. RESULTS: At deviations of up to 1.5σ below normative disc height, levels of apparent diffusion coefficient (ADC) and normalized T2 intensity were maintained. Once disc compression reached 1.5σ, there was a massive drop in ADC and normalized T2 intensity. Pfirrmann degeneration scores also increased after the 1.5σ mark. CONCLUSIONS: This study provides new, unbiased quantitative imaging tools to assess disc degeneration. We observed that these quantitative MRI measures indicate a threshold beyond which major pathological changes take place concurrently. Combined information from DHI, ADC and T2 images construct a set of novel biomarkers that could be used to identify degenerating discs that are approaching the threshold and possibly intervene before major pathologic changes occur.

A method for inducing and determining biomechanics associated with endplate fractures in the lumbar spine.

Lumbar spine endplate fracture is not easily detectible using medical imaging, but can lead to pain symptoms. Understanding endplate fracture mechanics can lead to more informed clinical diagnosis and more appropriate safety enhancements for civilian and military vehicles. Lumbar motion segments obtained from PMHS were prepared using two methods. Group 1 (n=6) was potted preserving the natural segmental lordosis while Group 2 (n=4) removed the curvature. Specimens were compressed at 0.5 mm/sec until fracture, observed via real-time fluoroscopy video as radio-opaque dye transferred from the intervertebral disc nucleus into the vertebral body. Fracture was confirmed using CT and dissection. Force, bony acoustics and disc pressure were correlates of fracture. Fractures in Group 1 (5 of 6 specimens) were concentrated in the posterior cortex of the inferior vertebral body whereas Group 2 experienced endplate fractures. The mean sagittal plane angle between endplates for specimens with cortical fracture was 5.1±1.2 degrees, compared to 1.0±0.5 degrees for endplate fracture. The average peak force for cortical fracture was 10.0±1.9 kN and 4.5±0.8 kN for endplate fracture. Pre-positioning during compressive loading has a significant role in determining whether a motion segment sustains a cortical or endplate fracture. Likewise, an appropriately oriented segment can sustain endplate fracture at approximately 45% of the load for cortex fracture.

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.

Mechanical yield of the lumbar annulus: a possible contributor to instability: Laboratory investigation.

OBJECT: Segmental instability in the lumbar spine can result from a number of mechanisms including intervertebral disc degeneration and facet joint degradation. Under traumatic circumstances, elevated loading may lead to mechanical yield of the annular fibers, which can decrease load-carrying capacity and contribute to instability. The purpose of this study was to quantify the biomechanics of intervertebral annular yield during tensile loading with respect to spinal level and anatomical region within the intervertebral disc. METHODS: This laboratory-based study incorporated isolated lumbar spine annular specimens from younger and normal or mildly degenerated intervertebral discs. Specimens were quasi-statically distracted to failure in an environmentally controlled chamber. Stress and strain associated with yield and ultimate failure were quantified, as was stiffness in the elastic and postyield regions. Analysis of variance was used to determine statistically significant differences based on lumbar spine level, radial position, and anatomical region of the disc. RESULTS: Annular specimens demonstrated a nonlinear response consisting of the following: toe region, linear elastic region, yield point, postyield region, and ultimate failure point. Regional dependency was identified between deep and superficial fibers. Mechanical yield was evident prior to ultimate failure in 98% of the specimens and occurred at approximately 80% and 74% of the stress and strain, respectively, to ultimate failure. Fiber modulus decreased by 34% following yield. CONCLUSIONS: Data in this study demonstrated that yielding of intervertebral disc fibers occurs relatively early in the mechanical response of the tissues and that stiffness is considerably decreased following yield. Therefore, yielding of annular fibers may result in decreased segmental stability, contributing to accelerated degeneration of bony components and possible idiopathic pain.

Cervical spine injury biomechanics: Applications for under body blast loadings in military environments.

BACKGROUND: While cervical spine injury biomechanics reviews in motor vehicle and sports environments are available, there is a paucity of studies in military loadings. This article presents an analysis on the biomechanics and applications of cervical spine injury research with an emphasis on human tolerance for underbody blast loadings in the military. METHODS: Following a brief review of published military studies on the occurrence and identification of field trauma, postmortem human subject investigations are described using whole body, intact head-neck complex, osteo-ligamentous cervical spine with head, subaxial cervical column, and isolated segments subjected to differing types of dynamic loadings (electrohydraulic and pendulum impact devices, free-fall drops). FINDINGS: Spine injuries have shown an increasing trend over the years, explosive devices are one of the primary causal agents and trauma is attributed to vertical loads. Injuries, mechanisms and tolerances are discussed under these loads. Probability-based injury risk curves are included based on loading rate, direction and age. INTERPRETATION: A unique advantage of human cadaver tests is the ability to obtain fundamental data to delineate injury biomechanics and establish human tolerance and injury criteria. Definitions of tolerances of the spine under vertical loads based on injuries have implications in clinical and biomechanical applications. Primary outputs such as forces and moments can be used to derive secondary variables such as the neck injury criterion. Implications are discussed for designing anthropomorphic test devices that may be used to predict injuries in underbody blast environments and improve the safety of military personnel.

Determination of peak deflections from human surrogates using chestbands in side impact tests.

To understand the biomechanics of the human body in motor vehicle environments, physical models including anthropomorphic test devices (ATD) and biological models (postmortem human surrogates) are used, and sled tests are conducted. Deflection is often used as a biomechanical variable to characterize the effects of impact loading and derive injury criteria. The objective of the present study was to evaluate different techniques and recommend a methodology to determine the peak thorax and abdominal deflections from temporal contours using chestbands in oblique lateral impacts. The side impact ATD WorldSID representing human surrogates was positioned on a seat. The seat was rigidly fixed to the platform of an acceleration sled. The oblique load-wall fixed to the sled consisted of separate and adjustable plates to contact the shoulder, thorax, abdomen, and pelvis. Two 59-gage chestbands were wrapped on the thorax and abdomen. Tests were conducted at low, medium, and high velocities (3.4, 6.7, and 7.5m/s) and three methods, termed the spine-sternum, bilateral, and spine-box, were used to determine the global peak deflection and its angulation. Results indicated that all three methods produced very similar angulations, for all velocity tests, and at both thorax and abdominal regions. However, maximum deflections were the lowest in the spine-sternum, followed by bilateral and spine-box methods, with one exception. Based on the development of deflection contours, locations used in the definitions of the origin, and accuracy in identifying critical locations/points in time-varying contours, results of the present study indicate that the bilateral method is the optimum procedure to determine the oblique peak deflection vector in biomechanical tests.

Biomechanics of human thoracolumbar spinal column trauma from vertical impact loading.

Recent studies suggest that dorsal spine injuries occur in motor vehicle crashes to restrained occupants. Compression/compression-flexion injuries occur in frontal crashes due to seat pan and vertical loading. While injuries, mechanisms and tolerances for neck injuries have been determined, thoraco-lumbar spine data are very limited. The objective of the study was to determine the biomechanical characteristics associated with such spinal injuries due to vertical loading. Upper thoracic (T2-T6), lower thoracic (T7-T11) and lumbar (T12-L5) columns from post mortem human surrogates were procured, fixed at the ends and dropped from three heights: the first two impacts designed as non-failure tests and the final was the failure test. Intermittent evaluations consisted of palpations and x-rays. Injuries were assessed using posttest x-rays and computed tomography scans. The age, stature, total body mass and body mass index of three PMHS were: 50 years, 164 cm, 66.9 kg, and 24.7 kg/m(2). The mean peak forces from 24 tests for the upper and lower thoracic and lumbar spines for varying drop heights ranged from 1.6 to 4.3, 1.3 to 5.1, and 1.3 to 6.7 kN, respectively. All peak forces increased with increasing drop heights. Injuries to the three spines included unstable vertebral body and posterior element (bipedicular and lamina) compression fractures and posterior complex disruptions. Logistic regression analysis indicated that peak forces of 3.4 and 3.7 kN are associated with 50% probability of fracture. These results indicate the initial tolerance limits of dorsal spines under vertical loading.

Upper and lower neck loads in belted human surrogates in frontal impacts.

The upper and lower neck loads in the restrained Hybrid III dummy and Test Device for Human Occupant Restraint (THOR) were computed in simulated frontal impact sled tests at low, medium, and high velocities; repeatability performance of the two dummies were evaluated at all energy inputs; peak forces and moments were compared with computed loads at the occipital condyles and cervical-thoracic junctions from tests using post mortem human surrogates (PMHS). A custom sled buck was used to position the surrogates. Repeated tests were conducted at each velocity for each dummy and sufficient time was allowed to elapse between the two experiments. The upper and lower neck forces and moments were determined from load cell measures and its locations with respect to the ends of the neck. Both dummies showed good repeatability for axial and shear forces and bending moments at all changes in velocity inputs. Morphological characteristics in the neck loading responses were similar in all surrogates, although the peak magnitudes of the variables differed. In general, the THOR better mimicked the PMHS response than the Hybrid III dummy, and factors such as neck design and chest compliance were attributed to the observed variations. While both dummies were not designed for use at the two extremes of the tested velocities, results from the present study indicate that, currently the THOR may be the preferred anthropomorphic testing device in crashworthiness research studies and full-scale vehicle tests at all velocities.

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.

Kinematic analysis of flailing injuries of lower extremities in side impacts.

The objective of the study was to determine the biomechanics of post mortem human subjects (PMHS) in lateral impact with a focus on lower extremity trauma and aviation safety for side-facing seat applications. Four male three-point belted intact PMHS were seated upright with the Frankfurt plane horizontal on a custom seat, covered with aircraft cushion. The seat had an armrest. The change in velocity from the Federal Aviation FAR25.562 standards was input to two specimens, and a lower energy input was used in the other two specimens. Pre-test and posttest x-rays were obtained, and autopsies were conducted. Sled and pelvic acceleration signals were digitally gathered and processed according to the Society of Automotive Engineers specifications. A high-speed digital video camera was used to track the frontal plane kinematics with targets placed at appropriate lower extremity landmarks. Fractures of the left distal femur-knee complex in one and proximal sub-capital femur in the other specimen occurred in tests using the simulated FAR pulse. Tests at the lower energy input in the other specimens did not result in trauma. Coronal motions in PMHS occurred from initial flailing of the lower leg-knee-upper leg complex initiating after the onset of the side-impact pulse with the armrest acting as a limiting/boundary condition for the left femur-pelvis-region. These motions were attributed to be a causal agent for the observed lower extremity injuries. Although from a limited sample size, the present findings indicate that lower extremities may sustain trauma, and side-facing seats in aviation environments may need to be evaluated for occupant safety in the lateral mode.

Injury differences between small and large overlap frontal crashes.

Because small overlap impacts have recently emerged as a crash mode posing great injury risk to occupants, a detailed analysis of US crash data was conducted using the NASS/CDS and CIREN databases. Frontal crashes were subcategorized into small overlap impact (SOI) and large overlap impact (LOI) using crash and crush characteristics from the datasets. Injuries to head, spine, chest, hip and pelvis, and lower extremities were parsed and compared between crash types. MAIS 3+ occupants in NASS/CDS and CIREN demonstrated increased incidence of head, chest, spine, and hip/pelvis injuries in SOI compared to LOI. In NASS/CDS, subgaleal hematoma represented 48.6% of SOI head injury codes but 27.6% in LOI. Cervical spine posterior element fractures also represented greater proportions of SOI spine injuries (e.g., facet fractures: 27.8 vs. 14.0%), and proximal femur fractures represented a greater proportion of hip/pelvis injuries (e.g., intertrochanteric fracture: 32.5 vs. 11.8%). Tarsal/metatarsal fractures were a lesser proportion of lower extremity injuries in SOI compared to LOI. Occupant contact points inducing these injuries were observed in CIREN cases in some instances without compartment intrusion. These injuries suggest the substantial role of occupant kinematics in SOI which may induce suboptimal occupant restraint interaction.

Comparison of head-neck responses in frontal impacts using restrained human surrogates.

The objective of the study was to evaluate the head and neck kinetics of three-point belted Hybrid III dummy and Test Device for Human Occupant Restraint (THOR) in frontal impacts, and compare their responses with data from post mortem human subjects (PMHS). Surrogates were placed on a buck, capable of accommodating different anthropometry with similar initial positioning. Duplicate tests were conducted at low, medium, and high (3.6, 6.9, and 15.8 m/s) velocities. Upper and lower neck forces and moments were determined from load cell measures and its locations with respect to the ends of the neck. Head excursion-time responses were more repeatable in the Hybrid III dummy than the THOR dummy. Hybrid III dummy response was more rigid in the sagittal plane. Peak THOR motions were closer to PMHS. Based on times of occurrences of peak excursions, THOR was closer to PMHS at all velocities, while Hybrid III dummy showed biofidelity at the medium and high velocities. Controlled positioning and testing with different surrogates provide an evaluation of inter-subject responses. THOR was more likely to "get the head where and when it needs to be" in frontal impacts. With the importance of testing at lower speeds due to recent recognition of real-world injuries, these data suggest that THOR may be an optimal dummy for frontal impacts. Comparisons of head-neck kinetic data with PMHS are valuable in frontal impact injury assessments.