Human pelvis injury risk curves from underbody blast impact.

INTRODUCTION: Underbody blast loading can result in injuries to the pelvis and the lumbosacral spine. The purpose of this study was to determine human tolerance in this region based on survival analysis. METHODS: Twenty-six unembalmed postmortem human surrogate lumbopelvic complexes were procured and pretest medical images were obtained. They were fixed in polymethylmethacrylate at the cranial end and a six-axis load cell was attached. The specimens were aligned in a seated soldier posture. Impacts were applied to the pelvis using a custom vertical accelerator. The experimental design consisted of non-injury and injury tests. Pretest and post-test X-rays and palpation were done following non-injury test, and after injury test medical imaging and gross dissections were done. Injuries were scored using the Abbreviated Injury Scale (AIS). Axial and resultant forces were used to develop human injury probability curves (HIPCs) at AIS 3+ and AIS 4 severities using survival analysis. Then ±95% CI was computed using the delta method, normalised CI size was obtained, and the quality of the injury risk curves was assigned adjectival ratings. RESULTS: At the 50% probability level, the resultant and axial forces at the AIS 3+ level were 6.6 kN and 5.9 kN, and at the AIS 4 level these were 8.4 kN and 7.5 kN, respectively. Individual injury risk curves along with ±95% CIs are presented in the paper. Increased injury severity increased the HIPC metrics. Curve qualities were in the good and fair ranges for axial and shear forces at all probability levels and for both injury severities. CONCLUSIONS: This is the first study to develop axial and resultant force-based HIPCs defining human tolerance to injuries to the pelvis from vertical impacts using parametric survival analysis. Data can be used to advance military safety under vertical loading to the seated pelvis.

Hierarchical process using Brier Score Metrics for lower leg injury risk curves in vertical impact.

INTRODUCTION: Parametric survival models are used to develop injury risk curves (IRCs) from impact tests using postmortem human surrogates (PMHS). Through the consideration of different output variables, input parameters and censoring, different IRCs could be created. The purpose of this study was to demonstrate the feasibility of the Brier Score Metric (BSM) to determine the optimal IRCs and derive them from lower leg impact tests. METHODS: Two series of tests of axial impacts to PMHS foot-ankle complex were used in the study. The first series used the metrics of force, time and rate, and covariates of age, posture, stature, device and presence of a boot. Also demonstrated were different censoring schemes: right and exact/uncensored (RC-UC) or right and uncensored/left (RC-UC-LC). The second series involved only one metric, force, and covariates age, sex and weight. It contained interval censored (IC) data demonstrating different censoring schemes: RC-IC-UC, RC-IC-LC and RC-IC-UC-LC. RESULTS: For each test set combination, optimal IRCs were chosen based on metric-covariate combination that had the lowest BSM value. These optimal IRCs are shown along with 95% CIs and other measures of interval quality. Forces were greater for UC than LC data sets, at the same risk levels (10% used in North Atlantic Treaty Organisation (NATO)). All data and IRCs are presented. CONCLUSIONS: This study demonstrates a novel approach to examining which metrics and covariates create the best parametric survival analysis-based IRCs to describe human tolerance, the first step in describing lower leg injury criteria under axial loading to the plantar surface of the foot.

Sensitivity of head and cervical spine injury measures to impact factors relevant to rollover crashes.

OBJECTIVE: Serious head and cervical spine injuries have been shown to occur mostly independent of one another in pure rollover crashes. In an attempt to define a dynamic rollover crash test protocol that can replicate serious injuries to the head and cervical spine, it is important to understand the conditions that are likely to produce serious injuries to these 2 body regions. The objective of this research is to analyze the effect that impact factors relevant to a rollover crash have on the injury metrics of the head and cervical spine, with a specific interest in the differentiation between independent injuries and those that are predicted to occur concomitantly. METHODS: A series of head impacts was simulated using a detailed finite element model of the human body, the Total HUman Model for Safety (THUMS), in which the impactor velocity, displacement, and direction were varied. The performance of the model was assessed against available experimental tests performed under comparable conditions. Indirect, kinematic-based, and direct, tissue-level, injury metrics were used to assess the likelihood of serious injuries to the head and cervical spine. RESULTS: The performance of the THUMS head and spine in reconstructed experimental impacts compared well to reported values. All impact factors were significantly associated with injury measures for both the head and cervical spine. Increases in impact velocity and displacement resulted in increases in nearly all injury measures, whereas impactor orientation had opposite effects on brain and cervical spine injury metrics. The greatest cervical spine injury measures were recorded in an impact with a 15° anterior orientation. The greatest brain injury measures occurred when the impactor was at its maximum (45°) angle. CONCLUSIONS: The overall kinetic and kinematic response of the THUMS head and cervical spine in reconstructed experiment conditions compare well with reported values, although the occurrence of fractures was overpredicted. The trends in predicted head and cervical spine injury measures were analyzed for 90 simulated impact conditions. Impactor orientation was the only factor that could potentially explain the isolated nature of serious head and spine injuries under rollover crash conditions. The opposing trends of injury measures for the brain and cervical spine indicate that it is unlikely to reproduce the injuries simultaneously in a dynamic rollover test.

Toward a more robust lower neck compressive injury tolerance-an approach combining multiple test methodologies.

OBJECTIVE: The compressive tolerance of the cervical spine has traditionally been reported in terms of axial force at failure. Previous studies suggest that axial compressive force at failure is particularly sensitive to the alignment of the cervical vertebra and the end conditions of the test methodology used. The present study was designed to develop a methodology to combine the data of previous experiments into a diverse data set utilizing multiple test methods to allow for the evaluation of the robustness of current and proposed eccentricity based injury criteria. METHODS: Data were combined from 2 studies composed of dynamic experiments including whole cervical spine and head kinematics that utilized different test methodologies with known end conditions, spinal posture, injury outcomes, and measured kinetics at the base of the neck. Loads were transformed to the center of the C7-T1 intervertebral disc and the eccentricity of the sagittal plane resultant force relative to the center of the disc was calculated. The correlation between sagittal plane resultant force and eccentricity at failure was evaluated and compared to the correlation between axial force and sagittal plane moment and axial force alone. RESULTS: Accounting for the eccentricity of the failure loads decreased the scatter in the failure data when compared to the linear combination of axial force and sagittal plane moment and axial force alone. A correlation between axial load and sagittal plane flexion moment at failure (R² = 0.44) was identified. The sagittal plane extension moment at failure did not have an identified correlation with the compressive failure load for the tests evaluated in this data set (R² = 0.001). The coefficients of determination for the linear combinations of sagittal plane resultant force with anterior and posterior eccentricity are 0.56 and 0.29, respectively. These correlations are an improvement compared to the combination of axial force and sagittal plane moment. CONCLUSIONS: Results using the outlined approach indicate that the combination of lower neck sagittal plane resultant force and the anterior-posterior eccentricity at which the load is applied generally correlate with the type of cervical damage identified. These results show promise at better defining the tolerance for compressive cervical fractures in male postmortem human subjects (PMHS) than axial force alone. The current analysis requires expansion to include more tolerance data so the robustness of the approach across various applied loading vectors and cervical postures can be evaluated.

ES2 neck injury assessment reference values for lateral loading in side facing seats.

Injury assessment reference values (IARV) predicting neck injuries are currently not available for side facing seated aircraft passengers in crash conditions. The aircraft impact scenario results in inertial loading of the head and neck, a condition known to be inherently different from common automotive side impact conditions as crash pulse and seating configurations are different. The objective of this study is to develop these IARV for the European Side Impact Dummy-2 (ES-2) previously selected by the US-FAA as the most suitable ATD for evaluating side facing aircraft seats. The development of the IARV is an extended analysis of previously published PMHS neck loads by identifying the most likely injury scenarios, comparing head-neck kinematics and neck loads of the ES2 versus PMHS, and development of injury risk curves for the ES2. The ES2 showed a similar kinematic response as the PMHS, particularly during the loading phase. The ES2 exhibited a stiffer response than the PMHS in the thoracic region, resulting in a faster rebound and smaller excursions in the vertical direction. Neck loads were consistent with results from previous authors and served as the basis for the ES2 neck injury risk curve developed here. Regression analysis of the previously published PMHS neck loads indicated that the tension force at the occipital condyles was the only neck load component with a significant correlation (Pearson r2 = 0.9158) to AIS3+ classified injuries. Tension force in the ES2 upper neck showed a weaker but still significant correlation with injury severity (r2 = 0.72) and is proposed to be used as an IARV with a tolerance of 2094 N for 50% AIS3+ risk. Although the prime focus of this study is on loading conditions typical in an aircraft crash environment, it is expected that the proposed IARV's can be used as an extension of typical automotive conditions, particularly for military vehicles and public transport applications where side facing upright seating configurations are more common.

Identification of vehicle components associated with severe thoracic injury in motor vehicle crashes: a CIREN and NASS analysis.

INTRODUCTION: Thoracic trauma secondary to motor vehicle crashes (MVC) continues to be a major cause of morbidity and mortality. Specific vehicle features may increase the risk of severe thoracic injury when striking the occupant. We sought to determine which vehicle contact points were associated with an increased risk of severe thoracic injury in MVC to focus subsequent design modifications necessary to reduce thoracic injury. METHODS: The National Automotive Sampling System (NASS) databases from 1993 to 2001 and the Crash Injury Research and Engineering Network (CIREN) databases from 1996 to 2004 were analyzed separately using univariate and multivariate logistic regression stratified by restraint use and crash direction. The risk of driver thoracic injury, defined as an abbreviated injury scale (AIS) of score > or =3, was determined as it related to specific points of contact between the vehicle and the driver. RESULTS: The incidence of severe chest injury in NASS and CIREN were 5.5% and 33%, respectively. The steering wheel, door panel, armrest, and seat were identified as contact points associated with an increased risk of severe chest injury. The door panel and arm rest were consistently a frequent cause of severe injury in both the NASS and CIREN data. CONCLUSIONS: Several vehicle contact points, including the steering wheel, door panel, armrest and seat are associated with an increased risk of severe thoracic injury when striking the occupant. These elements need to be further investigated to determine which characteristics need to be manipulated in order to reduce thoracic trauma during a crash.

Factors influencing occupant-to-seat belt interaction in far-side crashes.

Seat belt interaction with a far-side occupant's shoulder and thorax is critical to governing excursion towards the struck-side of the vehicle in side impact. In this study, occupant-to-belt interaction was simulated using a modified MADYMO human model and finite element belts. Quasi-static tests with volunteers and dynamic sled tests with PMHS and WorldSID were used for model validation and comparison. Parameter studies were then undertaken to quantify the effect of impact direction, seat belt geometry and pretension on occupant-to-seat belt interaction. Results suggest that lowering the D-ring and increasing pretension reduces the likelihood of the belt slipping off the shoulder. Anthropometry was also shown to influence restraint provided by the shoulder belt. Furthermore, the belt may slip off the occupant's shoulder at impact angles greater than 40 degrees from frontal when no pretension is used. However, the addition of pretension allowed the shoulder to engage the belt in all impacts from 30 to 90 degrees.

Lightweight low-profile nine-accelerometer package to obtain head angular accelerations in short-duration impacts.

Despite recognizing the importance of angular acceleration in brain injury, computations using data from experimental studies with biological models such as human cadavers have met with varying degrees of success. In this study, a lightweight and a low-profile version of the nine-accelerometer system was developed for applications in head injury evaluations and impact biomechanics tests. The triangular pyramidal nine-accelerometer package (PNAP) is precision-machined out of standard aluminum, is lightweight (65 g), and has a low profile (82 mm base width, 35 mm vertex height). The PNAP assures accurate orthogonal characteristics because all nine accelerometers are pre-aligned and attached before mounting on a human cadaver preparation. The feasibility of using the PNAP in human cadaver head studies is demonstrated by subjecting a specimen to an impact velocity of 8.1 m/s and the resultant angular acceleration peaked at 17 krad/s2. The accuracy and the high fidelity of the PNAP device at high and low angular acceleration levels were demonstrated by comparing the PNAP-derived angular acceleration data with separate tests using the internal nine-accelerometer head of the Hybrid III anthropomorphic test device. Mounting of the PNAP on a biological specimen such as a human cadaver head should yield very accurate angular acceleration data.

Validation of a head-neck computer model for whiplash simulation.

A head-neck computer model was comprehensively validated over a range of rear-impact velocities using experiments conducted by the same group of authors in the same laboratory. Validations were based on mean +/- 1 standard deviation response curves, i.e. corridors. Global head-neck angle, segmental angle and local facet joint regional kinematic responses from the model fell within experimental corridors. This was true for all impact velocities (1.3, 1.8 and 2.6 m s(-1)). The non-physiological S-curvature lasted approximately 100 ms. The present, comprehensively validated model can be used to conduct parametric studies and investigate the effects of factors such as active sequential and parallel muscle contractions, thoracic ramping and local tissue strain responses, as a function of cervical level, joint region and impact velocity in whiplash injury assessment.

Whiplash injury determination with conventional spine imaging and cryomicrotomy.

STUDY DESIGN: Soft tissue-related injuries to the cervical spine structures were produced by use of intact entire human cadavers undergoing rear-end impacts. Radiography, computed tomography, and cryomicrotomy techniques were used to evaluate the injury. OBJECTIVES: To replicate soft tissue injuries resulting from single input of whiplash acceleration to whole human cadavers simulating vehicular rear impacts, and to assess the ability of different modes of imaging to visualize soft tissue cervical lesions. SUMMARY OF BACKGROUND DATA: Whiplash-associated disorders such as headache and neck pain are implicated with soft tissue abnormalities to structures of the cervical spine. To the authors' best knowledge, no previous studies have been conducted to determine whether single cycle whiplash acceleration input to intact entire human cadavers can result in these soft tissue alterations. There is also a scarcity of data on the efficacy of radiography and computed tomography in assessing these injuries. METHODS: Four intact entire human cadavers underwent single whiplash acceleration (3.3 g or 4.5 g) loading by use of a whole-body sled. Pretest and posttest radiographs, computed tomography images, and sequential anatomic sections using a cryomicrotome were obtained to determine the extent of trauma to the cervical spine structures. RESULTS: Routine radiography identified the least number of lesions (one lesion in two specimens). Although computed tomography was more effective (three lesions in two specimens), trauma was not readily apparent to all soft tissues of the cervical spine. Cryomicrotome sections identified structural alterations in all four specimens to lower cervical spine components that included stretch and tear of the ligamentum flavum, anulus disruption, anterior longitudinal ligament rupture, and zygopophysial joint compromise with tear of the capsular ligaments. CONCLUSIONS: These results clearly indicate that a single application of whiplash acceleration pulse can induce soft tissue-related and ligament-related alterations to cervical spine structures. The pathologic changes identified in this study support previous observations from human volunteers observations with regard to the location of whiplash injury and may assist in the explanation of pain arising from this injury. Although computed tomography is a better imaging modality than radiography, subtle but clinically relevant injuries may be left undiagnosed with this technique. The cryomicrotome technique offers a unique procedure to understand and compare soft tissue-related injuries to the cervical anatomy caused by whiplash loading. Recognition of these injuries may advance the general knowledge of the whiplash disorder.

Contribution of disc degeneration to osteophyte formation in the cervical spine: a biomechanical investigation.

Cervical spine disorders such as spondylotic radiculopathy and myelopathy are often related to osteophyte formation. Bone remodeling experimental-analytical studies have correlated biomechanical responses such as stress and strain energy density to the formation of bony outgrowth. Using these responses of the spinal components, the present study was conducted to investigate the basis for the occurrence of disc-related pathological conditions. An anatomically accurate and validated intact finite element model of the C4-C5-C6 cervical spine was used to simulate progressive disc degeneration at the C5-C6 level. Slight degeneration included an alteration of material properties of the nucleus pulposus representing the dehydration process. Moderate degeneration included an alteration of fiber content and material properties of the anulus fibrosus representing the disintegrated nature of the anulus in addition to dehydrated nucleus. Severe degeneration included decrease in the intervertebral disc height with dehydrated nucleus and disintegrated anulus. The intact and three degenerated models were exercised under compression, and the overall force-displacement response, local segmental stiffness, anulus fiber strain, disc bulge, anulus stress, load shared by the disc and facet joints, pressure in the disc, facet and uncovertebral joints, and strain energy density and stress in the vertebral cortex were determined. The overall stiffness (C4-C6) increased with the severity of degeneration. The segmental stiffness at the degenerated level (C5-C6) increased with the severity of degeneration. Intervertebral disc bulge and anulus stress and strain decreased at the degenerated level. The strain energy density and stress in vertebral cortex increased adjacent to the degenerated disc. Specifically, the anterior region of the cortex responded with a higher increase in these responses. The increased strain energy density and stress in the vertebral cortex over time may induce the remodeling process according to Wolff's law, leading to the formation of osteophytes.

Biomechanics of calcaneal fractures: a model for the motor vehicle.

Changes in legislation, availability of passive or active restraint systems, or both, together with increased public awareness for safety and the need for use of restraint, have shifted the spectrum of trauma in motor vehicle crashes from the head and torso to other regions. Lower extremity trauma in motor vehicle crashes continues to be a significant problem. The objective of this study was to investigate the biomechanics of the human foot and ankle complex under impact loading and replicate calcaneal fractures routinely seen in motor vehicle crashes. Twenty-two unembalmed cadaver lower extremity specimens were subjected to dynamic loads using a minisled pendulum device. Input and output forces and results of pathologic analysis were obtained using load cell data, radiographs obtained before and after testing, and gross dissection. The intraarticular fracture patterns produced were similar to those seen clinically and described in the literature. Maximum forces ranged from 3.6 to 11.4 kN for the fracture, and 0.5 to 7.3 kN for the nonfracture groups. Logistic regression analysis revealed a 50% probability of calcaneal fracture at 5.5 kN and a 25% probability at 4.0 kN. These studies will lead to an understanding of the tolerance of the lower extremity in sustaining calcaneal fractures under impact. Implications of the work are in the design of crash test dummies, data acquisition, and modifications in motor vehicle design and safety.

Whiplash syndrome: kinematic factors influencing pain patterns.

STUDY DESIGN: The overall, local, and segmental kinematic responses of intact human cadaver head-neck complexes undergoing an inertia-type rear-end impact were quantified. High-speed, high-resolution digital video data of individual facet joint motions during the event were statistically evaluated. OBJECTIVES: To deduce the potential for various vertebral column components to be exposed to adverse strains that could result in their participation as pain generators, and to evaluate the abnormal motions that occur during this traumatic event. SUMMARY OF BACKGROUND DATA: The vertebral column is known to incur a nonphysiologic curvature during the application of an inertial-type rear-end impact. No previous studies, however, have quantified the local component motions (facet joint compression and sliding) that occur as a result of rear-impact loading. METHODS: Intact human cadaver head-neck complexes underwent inertia-type rear-end impact with predominant moments in the sagittal plane. High-resolution digital video was used to track the motions of individual facet joints during the event. Localized angular motion changes at each vertebral segment were analyzed to quantify the abnormal curvature changes. Facet joint motions were analyzed statistically to obtain differences between anterior and posterior strains. RESULTS: The spine initially assumed an S-curve, with the upper spinal levels in flexion and the lower spinal levels in extension. The upper C-spine flexion occurred early in the event (approximately 60 ms) during the time the head maintained its static inertia. The lower cervical spine facet joints demonstrated statistically greater compressive motions in the dorsal aspect than in the ventral aspect, whereas the sliding anteroposterior motions were the same. CONCLUSIONS: The nonphysiologic kinematic responses during a whiplash impact may induce stresses in certain upper cervical neural structures or lower facet joints, resulting in possible compromise sufficient to elicit either neuropathic or nociceptive pain. These dynamic alterations of the upper level (occiput to C2) could impart potentially adverse forces to related neural structures, with subsequent development of a neuropathic pain process. The pinching of the lower facet joints may lead to potential for local tissue injury and nociceptive pain.

Biomechanics of abdominal injuries.

Although considerable efforts have been advanced to investigate the biomechanical aspects of abdominal injuries, reviews have been very limited. The purpose of this article is to present a comprehensive review of the topic. Traumatic abdominal injuries occur due to penetrating or blunt loading. However, the present review is focused on blunt trauma. Because of the complexity of the abdomen, biomechanically relevant anatomical characteristics of the various abdominal organs are presented. The proposed mechanism of injury for these organs and methods for abdominal injury quantification are described. This is followed by a detailed analysis of the biomechanical literature with particular emphasis on experiments aimed to duplicate real world injuries and attempt to quantify trauma in terms of parameters such as force, deflection, viscous criteria, pressure criteria, and correlation of these variables with the severity of abdominal injury. Experimental studies include tests using primates, pigs, rats, beagles, and human cadavers. The effects of velocity, compression, padding, and impactor characteristics on tolerance; effects of pressurization and postmortem characteristics on abdominal injury; deduction of abdominal response corridors; and force-deflection responses (of the different abdominal regions and organs) are discussed. Output of initial research is presented on the development of a device to record the biomechanical parameters in an anthropomorphic test dummy during impact. Based on these studies and the current need for abdominal protection, recommendations are given for further research.

Development of extension kinematic corridors to validate a head/neck finite element model.

The objective of the current study was the development of experimental response corridors for the purpose of validating a finite element head-neck model in simulated vehicular rear impact. Six intact human head-neck cadaver complexes were used to understand and quantify the kinematics of the cervical spine secondary to low-speed rear impact. The first and second thoracic vertebrae were mounted in a fixative and attached to a minisled/pendulum apparatus. The specimens experienced live different input velocities applied to the first thoracic vertebral, created t),y the pendulum. The response of the specimen was digitally imaged at 1000 Hz from the right lateral side. Relative angles between vertebrae were analyzed in the sagittal plane at 100 ms after impact of the pendulum. Results correlated well with published physiologic range of motion data and dynamic full-body cadaver real impact experiments. Data obtained from this study will be used to validate the macroscopic motions of a finite element model, which will be used to understand the injury mechanisms involved in low-speed vehicular rear impacts.

Biomechanical modeling of penetrating traumatic head injuries: a finite element approach.

Due to advances in emergency medical care and modern techniques, treatment of gunshot wounds to the brain have improved and saved many lives. These advances were largely achieved using retrospective analysis of patients with recommendations for treatment. Biomechanical quantification of intracranial deformation/stress distribution associated with the type of weapon (e.g., projectile geometry) will advance clinical understanding of the mechanics of penetrating trauma. The present study was designed to delineate the biomechanical behavior of the human head under penetrating impact of two different projectile geometry using a nonlinear, three-dimensional finite element model. The human head model included the skull and brain. The qualitative comparison of the model output with each type of projectile during various time steps indicated that the deformation/stress progressed as the projectile penetrated the tissues. There is also a distinct difference in the patterns of displacement for each type of projectile. This observation matches our previous study using a physical gelatin model of delineate the penetrating wound profiles for different projectile types. The present study is a first step in the study of biomechanical modeling of penetrating traumatic brain injuries.

Pediatric neck injury scale factors and tolerance.

Although significant research efforts have been made to determine the tolerance for the adult neck, relatively little research has been conducted to derive the pediatric neck injury parameters. The existing approach to determine injury for the one, three and six year old pediatric populations is based on extrapolations from the adult male and calcaneal tendon tensile data. This study addresses the scale factors for pediatric age groups using data obtained from spinal components and neck geometry. The analysis included the determination of scale factors under extension, tension, compression and flexion loading modes as a function of age. The variations in biomechanical properties of each spinal component were determined from human cadaver studies. Active spinal components were identified under each loading mode and relationships were established for each component to obtain material-based scale factors. The scale factors and resulting injury tolerance values based on spine component material properties are more appropriate than values extrapolated from the calcaneal tendon.

Biomechanics of the cervical spine Part 2. Cervical spine soft tissue responses and biomechanical modeling.

OBJECTIVE: The responses and contributions of the soft tissue structures of the human neck are described with a focus on mathematical modeling. Spinal ligaments, intervertebral discs, zygapophysial joints, and uncovertebral joints of the cervical spine are included. Finite element modeling approaches have been emphasized. Representative data relevant to the development and execution of the model are discussed. A brief description is given on the functional mechanical role of the soft tissue components. Geometrical characteristics such as length and cross-sectional areas, and material properties such as force-displacement and stress-strain responses, are described for all components. Modeling approaches are discussed for each soft tissue structure. The final discussion emphasizes the normal and abnormal (e.g., degenerative joint disease, iatrogenic alteration, trauma) behaviors of the cervical spine with a focus on all these soft tissue responses. A brief description is provided on the modeling of the developmental biomechanics of the pediatric spine with a focus on soft tissues. Relevance. Experimentally validated models based on accurate geometry, material property, boundary, and loading conditions are useful to delineate the clinical biomechanics of the spine. Both external and internal responses of the various spinal components, a data set not obtainable directly from experiments, can be determined using computational models. Since soft tissues control the complex structural response, an accurate simulation of their anatomic, functional, and biomechanical characteristics is necessary to understand the behavior of the cervical spine under normal and abnormal conditions such as facetectomy, discectomy, laminectomy, and fusion.

Mechanisms and factors involved in hip injuries during frontal crashes.

This study was conducted to collect data and gain insights relative to the mechanisms and factors involved in hip injuries during frontal crashes and to study the tolerance of hip injuries from this type of loading. Unembalmed human cadavers were seated on a standard automotive seat (reinforced) and subjected to knee impact test to each lower extremity. Varying combinations of flexion and adduction/abduction were used for initial alignment conditions and pre-positioning. Accelerometers were fixed to the iliac wings and twelfth thoracic vertebral spinous process. A 23.4-kg padded pendulum impacted the knee at velocities ranging from 4.3 to 7.6 m/s. The impacting direction was along the anteroposterior axis, i.e., the global X-axis, in the body-fixed coordinate system. A load cell on the front of the pendulum recorded the impact force. Peak impact forces ranged from 2,450 to 10,950 N. The rate of loading ranged from 123 to 7,664 N/msec. The impulse values ranged from 12.4 to 31.9 Nsec. Injuries were not apparent in three tests. Eight tests resulted in trauma. Fractures involving the pelvis including the acetabulum and proximal femur occurred in five out of the eight tests, and distal femoral bone fracture occurred in one test. These results underscore the importance of leg pre-positioning and the orientation of the impacting axis to produce specific types of trauma to the pelvic region of the lower extremity.

Morphology of young and old cervical spine intervertebral disc tissues.

The intervertebral disc of the cervical spine undergoes degenerative changes during the aging process. Although many studies have reported the qualitative changes in the disc, methodology to quantify these changes is lacking. The present study was designed to quantify the geometrical variations of the nucleus pulposus, annulus fibrosus and uncovertebral joints. The age groups of specimens were classified as juvenile, adult and aged. Fresh intervertebral discs with adjacent vertebral bodies of the lower cervical spine of primates were isolated. The specimens were sectioned sequentially in a coronal plane. Sections were stained with Hematoxylin and Eosin, Verhoeff's, Safranin O, and Trichrome methods to distinguish the nucleus, annulus and uncovertebral joints. Histological images were examined using light microscopy and processed using a computer imaging program to trace the boundaries of the disc components. Dorsal-to-ventral depth and medial-to-lateral width of the nucleus pulposus, and its relative location to the annulus pulposus were also obtained. In the juvenile and adult discs, the nucleus appeared as a light opaque region with scattered notochordal cells with a clear distinction from the annulus region. In contrast, in the aged discs, the nucleus appeared as a dense region of amorphous, irregular collagen materials with less distinction from the annulus region. With the progression of aging, the dorsal-to-ventral depth of the nucleus decreased considerably compared to medial-to-lateral width. The uncovertebral joints were clear in the adult discs. The joints were less distinct in the aged discs and their size decreased. Quantification of three-dimensional geometrical variations will assist in better defining the disc tissue in the mathematical models.