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.

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.

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.

Use of postmortem human subjects to describe injury responses and tolerances.

Traumatic injuries from blunt, penetrating, and blast events expose the human body to unintentional and intentional external mechanical loads. To mitigate trauma and develop safety-engineered devices for clinical and bioengineering applications, it is critical to delineate the structural load-bearing anatomy and biomechanics of the various components of the human body. This article presents advances made in the understanding of the injury responses and tolerances through experiments conducted using intact or segmented tissues from postmortem human subjects (PMHS), and a considerable majority of data for the presentation has been extracted from studies conducted at the Institutions of the authors. The role of the PMHS model for studying traumatic injuries to the head and face, vertebral column (cervical, thoracic and lumbar spines), thorax, abdomen, pelvis, and lower extremities is discussed. Different impact loading scenarios, likely responsible for the initial trauma causation, are considered in the analysis and determination of the human response to injury. Clinical advances made using the PMHS model are discussed. This includes vertebral stabilization system evaluations secondary to traumatic injuries to the spinal column. The critical importance of using data from the PMHS model in developing validated computational models for advancing crashworthiness research, occupant safety in motor vehicle crashes, medical devices, and safety-engineering applications is highlighted.

The relationship between lower neck shear force and facet joint kinematics during automotive rear impacts.

A primary goal of biomechanical safety research is the definition of localized injury thresholds in terms of quantities that are repeatable and easily measureable during experimentation. Recent biomechanical experimentation using human cadavers has highlighted the role of lower cervical facet joints in the injury mechanism resulting from low-speed automotive rear impacts. The present study was conducted to correlate lower neck forces and moments with facet joint motions during simulated rear impacts in an effort to define facet joint injury tolerance thresholds that can be used to assess automobile safety. Four male and four female intact head-neck complexes were obtained from cadaveric specimens and subjected to simulated automotive rear impacts using a pendulum-minisled device. Cervical spine segmental angulations and localized facet joint kinematics were correlated to shear and axial forces, and bending moments at the cervico-thoracic junction using linear regression. R(2) coefficients indicated that spinal kinematics correlated well with lower neck shear force and bending moment. Correlation slope was steeper in female specimens, indicating greater facet joint motions for a given loading magnitude. This study demonstrated that lower neck loads can be used to predict lower cervical facet joint kinematics during automotive rear impacts. Higher correlation slope in female specimens corresponds to higher injury susceptibility in that population. Although lower neck shear force and bending moment demonstrated adequate correlation with lower cervical facet joint motions, shear force is likely the better predictor due to similarity in the timing of peak magnitudes with regard to maximum facet joint motions.

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.

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.

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.

Moment-rotation responses of the human lumbosacral spinal column.

The objective of this study was to test the hypothesis that the human lumbosacral joint behaves differently from L1-L5 joints and provides primary moment-rotation responses under pure moment flexion and extension and left and right lateral bending on a level-by-level basis. In addition, range of motion (ROM) and stiffness data were extracted from the moment-rotation responses. Ten T12-S1 column specimens with ages ranging from 27 to 68 years (mean: 50.6+/-13.2) were tested at a load level of 4.0 N m. Nonlinear flexion and extension and left and right lateral bending moment-rotation responses at each spinal level are reported in the form of a logarithmic function. The mean ROM was the greatest at the L5-S1 level under flexion (7.37+/-3.69 degrees) and extension (4.62+/-2.56 degrees) and at the L3-L4 level under lateral bending (4.04+/-1.11 degrees). The mean ROM was the least at the L1-L2 level under flexion (2.42+/-0.90 degrees), L2-L3 level under extension (1.58+/-0.63 degrees), and L1-L2 level under lateral bending (2.50+/-0.75 degrees). The present study proved the hypothesis that L5-S1 motions are significantly greater than L1-L5 motions under flexion and extension loadings, but the hypothesis was found to be untrue under the lateral bending mode. These experimental data are useful in the improved validation of FE models, which will increase the confidence of stress analysis and other modeling applications.

Injury patterns in side pole crashes.

Side impact pole/tree crashes can have devastating consequences. A series of 53 CIREN cases of narrow-object side impacts were analyzed. Twenty-seven of 53 had serious chest injury and 27 had serious head injury. Unilateral chest trauma led to the examination of residual crush pattern that often demonstrated oblique door intrusion into the occupant thorax space. It was hypothesized that unilateral chest trauma was caused by antero-lateral chest loading. This hypothesis was evaluated by conducting two (PMHS and ES2) vehicle side impact tests into a rigid pole. The PMHS test produced an oblique chest deformation pattern with injuries very similar to the real world trauma: unilateral rib fractures, spleen laceration, pelvic fracture, and a basilar skull fracture. Narrow-object side impacts are severe crash environments that can induce oblique chest loading and unique head trauma. Because the human may be more vulnerable in this type of crash scenario, dummy response and measurements, as well as a re-examination of side injury criteria may be necessary to design appropriate injury-mitigating safety devices.

Minimally invasive, extracavitary approach for thoracic disc herniation: technical report and preliminary results.

BACKGROUND: Traditional approaches to thoracic disc herniation are technically demanding and, if incorporating thoracotomy, can be associated with significant morbidity. New procedures have allowed discectomy with less pain and morbidity. PURPOSE: To assess the feasibility, safety, and early outcome of a minimally invasive extracavitary approach (MI-ECA) for thoracic disc disease. STUDY DESIGN: Cadaver sessions and a short-term human study were performed on four cadavers and 10 patients, respectively. Operative results and complications were studied, and early outcome was assessed using a Visual Pain Analog Scale, neurological status, and American Spinal Injury Association (ASIA) classification. METHODS: Four fresh cadaver sessions, attempting all thoracic levels, were completed to determine the feasibility of the technique. Ten patients with thoracic myelopathy caused by herniated disc were treated using the minimally invasive extracavitary approach. RESULTS: Intervertebral discs were successfully removed from all four cadavers using this procedure. No operative complications in the human series were documented. The mean operative time was 171 minutes (150-220), mean estimated blood loss was 215 cc (60-350), and hospital stay for all patients was one night. No operative or postoperative complications were encountered. All patients returned to work within 4 weeks after discharge. Postoperative ASIA scores improved in three patients who had motor or sensory findings. Tone improved in all patients. Mean pain outcome using the Visual Pain Analog Scale was 1.5 (0-3). CONCLUSION: Our early experience suggests that MI-ECA may be a valuable option in the management of thoracic disc herniation.

Tapered cages in anterior lumbar interbody fusion: biomechanics of segmental reactions.

OBJECT: The aim of this study was to determine the in vitro biomechanical responses of lumbar spinal segments after implantation of tapered cages. METHODS: Range of motion (ROM)- and stiffness-related data were determined in 10 human cadaveric T12-S1 columns subjected to flexion, extension, and lateral bending modes before and after anterior lumbar interbody fusion in which stand-alone LT-CAGE devices were used. The overall column showed no significant changes in ROM or stiffness. At the instrumented level, stiffness increased significantly (p < 0.05) in flexion and lateral bending modes. Indications of instability in extension were present, but these values were not statistically significant. There was no evidence of adjacent-level instability at any level in any mode, except for the segment superior to the fixation level in flexion; here there was a significant increase in ROM (p < 0.05) and a decrease in stiffness. CONCLUSIONS: The anatomical conformity and bilateral placement of cages provide ample stability and rigidity at the treated level, comparable to that of other cage systems. Because hypermobility is traditionally related to early degenerative changes, the present results appear to suggest that cages do not significantly contribute to such alterations.

Validation of a clinical finite element model of the human lumbosacral spine.

Very few finite element models on the lumbosacral spine have been reported because of its unique biomechanical characteristics. In addition, most of these lumbosacral spine models have been only validated with rotation at single moment values, ignoring the inherent nonlinear nature of the moment-rotation response of the spine. Because a majority of lumbar spine surgeries are performed between L4 and S1 levels, and the confidence in the stress analysis output depends on the model validation, the objective of the present study was to develop a unique finite element model of the lumbosacral junction. The clinically applicable model was validated throughout the entire nonlinear range. It was developed using computed tomography scans, subjected to flexion and extension, and left and right lateral bending loads, and quantitatively validated with cumulative variance analyses. Validation results for each loading mode and for each motion segment (L4-L5, L5-S1) and bisegment (L4-S1) are presented in the paper.

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.

Clinical and radiological relationship between posterior lumbar interbody fusion and posterolateral lumbar fusion.

BACKGROUND: Posterolateral lumbar fusion (PLF) is the most popular technique for stabilizing the lumbar spine. Biomechanically, PLF decreases segmental motion in the posterior column, which presumably reduces facet joint pain. Posterior lumbar interbody fusion (PLIF) may decompress nerve roots by distracting the collapsed disc space, and achieving optimal fusion in relation to load-bearing capacity. The purpose of the study was to examine the role of interbody fixation vs pedicle fixation in transverse lumbar fusion and to assess treated and adjacent disc space height changes over time. METHODS: One hundred patients who underwent PLIF and noninstrumented transverse process fusion (n = 55) or instrumented PLF (n = 45) between 1996 and 1998 were evaluated retrospectively. Outpatient charts and follow-up films were reviewed. Bone fusion was determined using Brantigan and Steffee's classification and clinical outcome by the Prolo scale. Disc space heights at the fusion and adjacent levels were measured. Analysis of variance and chi(2) statistical techniques were used for data analysis. RESULTS: Disc space height was increased and better maintained in PLIF patients. PLIF resulted in a nonsignificant tendency toward higher fusion rates. No differences in clinical and functional outcomes were found between the groups. There was no correlation between preservation of disc space height and clinical outcome. CONCLUSIONS: Disc space height does not seem to impact clinical outcome in lumbar fusion, and efforts to maintain it may be unwarranted.

Type II odontoid fracture from frontal impact: case report and biomechanical mechanism of injury.

The authors report a case of Type II odontoid fracture from a frontal impact sustained in the crash of a late-model motor vehicle. They discuss the biomechanical mechanisms of injury after considering patient demographic data, type and use of restraint systems including seatbelt and airbags, crash characteristics, and laboratory-based experimental studies. Multiple factors contributed to the Type II odontoid fracture: the patient's tall stature and intoxicated state; lack of manual three-point seat belt use; obliqueness of the frontal impact; and the most likely preflexed position of the head-neck complex at the time of impact, which led to contact of the parietal region with the A-pillar roof-rail area of the vehicle and resulted in the transfer of the dynamic compressive force associated with lateral bending. Odontoid fractures still occur in individuals involved in late-model motor vehicle frontal crashes, and because this injury occurs secondary to head impact, airbags may not play a major role in mitigating this type of trauma to an unrestrained occupant. It may be more important to use seat belts than to depend on the airbag alone for protection from injury.

Preinjury cervical alignment affecting spinal trauma.

OBJECT: The authors tested the hypothesis that initial alignment of the head-neck complex affects cervical spine injury mechanism, trauma rating, injury classification based on stability, and fracture pattern. METHODS: Thirty intact human cadaveric head-neck complexes were prepared by fixing the thoracic end in polymethylmethacrylate. The cranium was unconstrained. The initial spinal alignment was described in terms of eccentricity, defined as the anteroposterior position of the occipital condyles with respect to the T-1 vertebral body. The specimens were subjected to impact loading delivered using an electrohydraulic testing device. Outcomes after injury were identified using radiography and computerized tomography. The mechanisms of injury were classified according to fracture pattern into compression-extension, compression-flexion, hyperflexion, and vertical compression. Trauma was graded according to the Abbreviated Injury Scale rating system. Based on clinical assessment, injuries were classified as stable or unstable. Injuries were also classified into bone fracture or nonfracture groups. Analysis of variance tests were used to determine the influence of eccentricity on spinal injury outcomes. Eccentricity significantly influenced the mechanism of injury (p < 0.0001), trauma rating (p < 0.005), and fracture (p < 0.0001) classification. Statistically significant differences, however, were not apparent when the classification of injury was based on stability considerations. CONCLUSIONS: Spinal alignment is a strong determinant of the biomechanics of impact-induced cervical spine injury.