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.     

Investigation of Motorcyclist Cervical Spine Trauma Using HUMOS Model

Objective: With 16 percent of the total road user fatalities, motorcyclists represent the second highest rate of road fatalities in France after car occupants. Regarding road accidents, a large proportion of trauma was on the lower cervical spine. According to different clinical studies, it is postulated that the cervical spine fragility areas are located on the upper and lower cervical spine. In motorcycle crashes, impact conditions occur on the head segment with various orientations and impact directions, leading to a combination of rotations and compression. Hence, motorcyclist vulnerability was investigated considering many impact conditions. Method: Using the human model for safety (HUMOS), a finite element model, this work aims to provide an evaluation of the cervical spine weaknesses based on an evaluation of injury mechanisms. This evaluation consisted of defining 2 injury risk factors (joint injury and bone fracture) using a design of experiment including various velocities, impact directions, and impact orientations. Results: The results confirmed previously reported clinical and epidemiological work on the fragility of the lower cervical spine and the upper cervical spine segments. Joint injuries appeared before bone fractures on both the upper and lower cervical spine. Bone fracture risk was greater on the lower cervical spine than on the upper cervical spine. The compression induced by a high impact angle was identified as an important injury severity factor. It significantly increased the injury incidence for both joint injuries and bone fractures. It also induced a shift in injury location from the lower to the upper cervical spine. The impact velocity exhibited a linear relationship with injury risks and severity. It also shifted the bone fracture risk from the lower to upper spinal segments.     

The effect of muscle activation on neck response

Prevention of neck injuries due to complex loading, such as occurs in traffic accidents, requires knowledge of neck injury mechanisms and tolerances. The influence of muscle activation on outcome of the injuries is not clearly understood. Numerical simulations of neck injury accidents can contribute to increase the understanding of injury tolerances. The finite element (FE) method is suitable because it gives data on stress and strain of individual tissues that can be used to predict injuries based on tissue level criteria.The aim of this study was to improve and validate an anatomically detailed FE model of the human cervical spine by implement neck musculature with passive and active material properties. Further, the effect of activation time and force on the stresses and strains in the cervical tissues were studied for dynamic loading due to frontal and lateral impacts.The FE model used includes the seven cervical vertebrae, the spinal ligaments, the facet joints with cartilage, the intervertebral disc, the skull base connected to a rigid head, and a spring element representation of the neck musculature. The passive muscle properties were defined with bilinear force-deformation curves and the active properties were defined using a material model based on the Hill equation. The FE model's responses were compared to volunteer experiments for frontal and lateral impacts of 15 and 7 g. Then, the active muscle properties where varied to study their effect on the motion of the skull, the stress level of the cortical and trabecular bone, and the strain of the ligaments.The FE model had a good correlation to the experimental motion corridors when the muscles activation was implemented. For the frontal impact a suitable peak muscle force was 40 N/cm2 whereas 20 N/cm2 was appropriate for the side impact. The stress levels in the cortical and trabecular bone were influenced by the point forces introduced by the muscle spring elements; therefore a more detailed model of muscle insertion would be preferable. The deformation of each spinal ligament was normalized with an appropriate failure deformation to predict soft tissue injury. For the frontal impact, the muscle activation turned out to mainly protect the upper cervical spine ligaments, while the musculature shielded all the ligaments disregarding spinal level for lateral impacts. It is concluded that the neck musculature does not have the same protective properties during different impacts loadings.     

Motorcycle helmets and spinal cord injury: helmet usage and type

The objective of this study was to assess the role of helmets and helmet type in relation to injury to the cervical spinal cord. It was based on a consecutive series of 110 motorcyclists with neurological damage to the spinal cord admitted alive (referred to as acute survivors) to a specialist spinal cord injuries unit at an Australian hospital. Cases were those with injury to the cervical spinal cord and controls were those with injury to the cord of other segments of the spine. The study showed that there was no significant difference in the odds of cervical spinal cord injury among unhelmeted and helmeted motorcyclist acute survivors. In addition, it confirmed the findings of a recently published Australian fatality study demonstrating no difference in the odds of cervical spinal cord injury among full-face and open-face helmet wearers. These results contrasted with the findings of earlier studies. In consideration of the limitations of existing research on the role of helmets in spinal cord injury, further study is required based on a larger series or a series having a higher proportion of non-wearers and open-face helmet wearers, including both survivors and those killed, and including assessment of cord and non-cord spinal injuries separately, helmet type, head impact, and helmet retention.     

Motor vehicle restraint system use and risk of spine injury

OBJECTIVE: Motor vehicle collision (MVC)-related spinal injury is a severe and often permanently disabling injury. In addition, strain injuries have been reported as a common outcome of MVCs. Although advances in automobile crashworthiness have reduced both fatalities and severe injuries, the impact of varying occupant restraint systems (seatbelts and airbags) on thoracolumbar spine injuries is unknown. This study examined the relationship between the occurrence of mild to severe cervical and thoracolumbar spine injury and occupant restraint systems among front seat occupants involved in frontal MVCs. METHODS: A retrospective cohort study was conducted among subjects obtained from the 1995-2004 National Automotive Sampling System. Cases were identified based on having sustained a spine injury of >/=1 on the Abbreviated Injury Scale (AIS), 1990 Revision. Risk risks (RRs) and 95% confidence intervals (CIs) were computed comparing occupant restraint systems with unrestrained occupants. RESULTS: We found an overall incidence of AIS1 cervical (11.8%) and thoracolumbar (3.7%) spinal injury. Seatbelt only restraints were associated with increased cervical AIS1 injury (RR = 1.40, 95% CI 1.04-1.88). However, seatbelt only restraints showed the greatest risk reduction for AIS2 spinal injuries. Airbag only restraints reduced thoracolumbar AIS1 injuries (RR = 0.29, 95% CI 0.08-1.04). Seatbelt combined with airbag use was protective for cervical AIS3+ injury overall (RR = 0.29, 95% CI 0.14-0.58), cervical neurological injury (RR = 0.19, 95% CI 0.05-0.81), and thoracolumbar AIS3+ injury overall (RR = 0.20, 95% CI 0.05-0.70). CONCLUSIONS: The results of this study suggest that seatbelts alone or in combination with an airbag increased the incidence of AIS1 spinal injuries, but provide protection against more severe injury to all regions of the spine. Airbag deployment without seatbelt use did not show increased protection relative to unrestrained occupants.     

Cervical spine loads and intervertebral motions during whiplash

OBJECTIVE: To quantify the dynamic loads and intervertebral motions throughout the cervical spine during simulated rear impacts. METHODS: Using a biofidelic whole cervical spine model with muscle force replication and surrogate head and bench-top mini-sled, impacts were simulated at 3.5, 5, 6.5, and 8 g horizontal accelerations of the T1 vertebra. Inverse dynamics was used to calculate the dynamic cervical spine loads at the centers of mass of the head and vertebrae (C1-T1). The average peak loads and intervertebral motions were statistically compared (P < 0.05) throughout the cervical spine. RESULTS: Load and motion peaks generally increased with increasing impact acceleration. The average extension moment peaks at the lower cervical spine, reaching 40.7 Nm at C7-T1, significantly exceeded the moment peaks at the upper and middle cervical spine. The highest average axial tension peak of 276.9 N was observed at the head, significantly greater than at C4 through T1. The average axial compression peaks, reaching 223.2 N at C5, were significantly greater at C4 through T1, as compared to head-C1. The highest average posterior shear force peak of 269.5 N was observed at T1. CONCLUSION: During whiplash, the cervical spine is subjected to not only bending moments, but also axial and shear forces. These combined loads caused both intervertebral rotations and translations.     

Estimated Injury Risk for Specific Injuries and Body Regions in Frontal Motor Vehicle Crashes

Objective: Injury risk curves estimate motor vehicle crash (MVC) occupant injury risk from vehicle, crash, and/or occupant factors. Many vehicles are equipped with event data recorders (EDRs) that collect data including the crash speed and restraint status during a MVC. This study's goal was to use regulation-required data elements for EDRs to compute occupant injury risk for (1) specific injuries and (2) specific body regions in frontal MVCs from weighted NASS-CDS data.

Methods: Logistic regression analysis of NASS-CDS single-impact frontal MVCs involving front seat occupants with frontal airbag deployment was used to produce 23 risk curves for specific injuries and 17 risk curves for Abbreviated Injury Scale (AIS) 2+ to 5+ body region injuries. Risk curves were produced for the following body regions: head and thorax (AIS 2+, 3+, 4+, 5+), face (AIS 2+), abdomen, spine, upper extremity, and lower extremity (AIS 2+, 3+). Injury risk with 95% confidence intervals was estimated for 15–105 km/h longitudinal delta-Vs and belt status was adjusted for as a covariate.

Results: Overall, belted occupants had lower estimated risks compared to unbelted occupants and the risk of injury increased as longitudinal delta-V increased. Belt status was a significant predictor for 13 specific injuries and all body region injuries with the exception of AIS 2+ and 3+ spine injuries. Specific injuries and body region injuries that occurred more frequently in NASS-CDS also tended to carry higher risks when evaluated at a 56 km/h longitudinal delta-V. In the belted population, injury risks that ranked in the top 33% included 4 upper extremity fractures (ulna, radius, clavicle, carpus/metacarpus), 2 lower extremity fractures (fibula, metatarsal/tarsal), and a knee sprain (2.4–4.6% risk). Unbelted injury risks ranked in the top 33% included 4 lower extremity fractures (femur, fibula, metatarsal/tarsal, patella), 2 head injuries with less than one hour or unspecified prior unconsciousness, and a lung contusion (4.6–9.9% risk). The 6 body region curves with the highest risks were for AIS 2+ lower extremity, upper extremity, thorax, and head injury and AIS 3+ lower extremity and thorax injury (15.9–43.8% risk).

Conclusions: These injury risk curves can be implemented into advanced automatic crash notification (AACN) algorithms that utilize vehicle EDR measurements to predict occupant injury immediately following a MVC. Through integration with AACN, these injury risk curves can provide emergency medical services (EMS) and other patient care providers with information on suspected occupant injuries to improve injury detection and patient triage.     

Cervical and thoracic spine injury in pediatric motor vehicle crash passengers

Objective: Motor vehicle occupants aged 8 to 12 years are in transition, in terms of both restraint use (booster seat or vehicle belt) and anatomical development. Rear-seated occupants in this age group are more likely to be inappropriately restrained than other age groups, increasing their vulnerability to spinal injury. The skeletal anatomy of an 8- to 12-year-old child is also in developmental transition, resulting in spinal injury patterns that are unique to this age group. The objective of this study is to identify the upper spine injuries commonly experienced in the 8- to 12-year-old age group so that anthropomorphic test devices (ATDs) representing this size of occupant can be optimized to predict the risk of these injuries.

Methods: Motor vehicle crash cases from the National Trauma Data Bank (NTDB) were analyzed to characterize the location and nature of cervical and thoracic spine injuries in 8- to 12-year-old crash occupants compared to younger (age 0–7) and older age groups (age 13–19, 20–39).

Results: Spinal injuries in this trauma center data set tended to occur at more inferior vertebral levels with older age, with patients in the 8- to 12-year-old group diagnosed with thoracic injury more frequently than cervical injury, in contrast to younger occupants, for whom the proportion of cases with cervical injury outnumbered the proportion of cases with thoracic injury. With the cervical spine, a higher proportion of 8- to 12-year-olds had upper spine injury than adults, but a substantially lower proportion of 8- to 12-year-olds had upper spine injury than younger children. In terms of injury type, the 8- to 12-year-old group’s injury patterns were more similar to those of teens and adults, with a higher relative proportion of fracture than younger children, who were particularly vulnerable to dislocation and soft tissue injuries. However, unlike for adults and teens, catastrophic atlanto-occipital dislocations were still more common than any other type of dislocation for 8- to 12-year-olds and vertebral body fractures were particularly frequent in this age group.

Conclusions: Spinal injury location in the cervical and thoracic spine moved downward with age in this trauma center data set. This shift in injury pattern supports the need for measurement of thoracic and lower cervical spine loading in ATDs representing the 8- to 12-year-old age group.     

Response of the Head,Neck and Torso to Pendulum Impacts on the Back

Pendulum impacts on the back were conducted to determine human head, neck and torso biomechanics. Eight unembalmed cadavers were subjected to 23.4 kg pendulum impacts at 4.4 m/s and 6.6 m/s at T1 and T6. Twenty-four tests were conducted with accelerometers on the pendulum, spine, torso, and head in the WSU 3-2-2-2 array. High-speed photography was taken. Impact displaces the torso forward, deflects the chest, displaces and rotates the head, and extends the neck. Average responses and corridors were determined for head kinematics and chest force-deflection. The head-neck response occurs in two phases. First, the head displaces upwards and rearwards 30—40 mm with respect to the torso along a 45° trajectory. Head rotation is 1O°-15° with essentially no neck moment, but high neck compression forces. Second, the head rotates from 10°-15° to 40°-55° starting with a rapid rise in neck moment and displaces 80–100 mm rearward. Anterior cervical fractures correlate with neck tension. Rib fractures correlate with impact force and chest deflection. This study provides chest bio-mechanical responses for rear impacts resulting in head displacement and rotation, neck extension and cervical-thoracic injury.     

A 6-year survey of road traffic accidents in Southwest China: Emphasis on traumatic brain injury

Background: The objective of this study is to provide an up-to-date overview of the patterns of injuries, especially traumatic brain injury (TBI) caused by RTAs and to discuss some of the public health consequences. Methods: A scientific team was established to collect road traffic accidents occurring between 2013 and 2018 in Chongqing, Southwest China. For each accident, the environment-, vehicle-, and person- variables were analyzed and determined. The overall injury distribution and TBI patterns of four types of road users (driver, passenger, motorcyclist and pedestrian) were compared. The environmental and time distribution of accidents with TBI were shown by bar and pie chart. The risks of severe brain injury whether motorcyclist wearing helmets or not were compared and the risk factors of severe TBI in pedestrian were determined by odds ratio analysis. Results: This study enrolled 2131 accidents with 2741 persons of all kind of traffic participants, 1149 of them suffered AIS1+ head injury and 1598(58%) died in 7 days. The most common cause of deaths is due to head injury with 714(85%) and 1266(79%) persons died within 2 hours. Among 423 persons suffered both skull fracture and intracranial injury, 102 (24.1%) have an intracranial injury but no skull fractures, while none of the skull fractures without intracranial injury was found. Besides, motorcyclists without a helmet were at higher risks for all the brain injury categories. The risk of pedestrian suffering severe TBI at an impact speed of more than 70 km/h is 100 times higher than that with an impact speed of less than 40 km/h. Conclusion: It is urgently needed to develop a more reliable brain injury evaluation criterion for better protection of the road users. We believe that strengthening the emergency care to head injury at the scene is the most effective way to reduce traffic fatality.     

Role of age and injury mechanism on cervical spine injury tolerance from head contact loading

Objective: The objective of this study was to determine the influence of age and injury mechanism on cervical spine tolerance to injury from head contact loading using survival analysis.

Methods: This study analyzed data from previously conducted experiments using post mortem human subjects (PMHS). Group A tests used the upright intact head–cervical column experimental model. The inferior end of the specimen was fixed, the head was balanced by a mechanical system, and natural lordosis was removed. Specimens were placed on a testing device via a load cell. The piston applied loading at the vertex region. Spinal injuries were identified using medical images. Group B tests used the inverted head–cervical column experimental model. In one study, head–T1 specimens were fixed distally, and C7–T1 joints were oriented anteriorly, preserving lordosis. Torso mass of 16 kg was added to the specimen. In another inverted head–cervical column study, occiput–T2 columns were obtained, an artificial head was attached, T1–T2 was fixed, C4–C5 disc was maintained horizontal in the lordosis posture, and C7–T1 was unconstrained. The specimens were attached to the drop test carriage carrying a torso mass of 15 kg. A load cell at the inferior end measured neck loads in both studies. Axial neck force and age were used as the primary response variable and covariate to derive injury probability curves using survival analysis.

Results: Group A tests showed that age is a significant (P < .05) and negative covariate; that is, increasing age resulted in decreasing force for the same risk. Injuries were mainly vertebral body fractures and concentrated at one level, mid-to-lower cervical spine, and were attributed to compression-related mechanisms. However, age was not a significant covariate for the combined data from group B tests. Both group B tests produced many soft tissue injuries, at all levels, from C1 to T1. The injury mechanism was attributed to mainly extension. Multiple and noncontiguous injuries occurred. Injury probability curves, ±95% confidence intervals, and normalized confidence interval sizes representing the quality of the mean curve are given for different data sets.

Conclusions: For compression-related injuries, specimen age should be used as a covariate or individual specimen data may be prescaled to derive risk curves. For distraction- or extension-related injuries, however, specimen age need not be used as a covariate in the statistical analysis. The findings from these tests and survival analysis indicate that the age factor modulates human cervical spine tolerance to impact injury.     

Effects of whole spine alignment patterns on neck responses in rear end impact

Objective: The aim of this study was to investigate the whole spine alignment in automotive seated postures for both genders and the effects of the spinal alignment patterns on cervical vertebral motion in rear impact using a human finite element (FE) model.

Methods: Image data for 8 female and 7 male subjects in a seated posture acquired by an upright open magnetic resonance imaging (MRI) system were utilized. Spinal alignment was determined from the centers of the vertebrae and average spinal alignment patterns for both genders were estimated by multidimensional scaling (MDS). An occupant FE model of female average size (162 cm, 62 kg; the AF 50 size model) was developed by scaling THUMS AF 05. The average spinal alignment pattern for females was implemented in the model, and model validation was made with respect to female volunteer sled test data from rear end impacts. Thereafter, the average spinal alignment pattern for males and representative spinal alignments for all subjects were implemented in the validated female model, and additional FE simulations of the sled test were conducted to investigate effects of spinal alignment patterns on cervical vertebral motion.

Results: The estimated average spinal alignment pattern was slight kyphotic, or almost straight cervical and less-kyphotic thoracic spine for the females and lordotic cervical and more pronounced kyphotic thoracic spine for the males. The AF 50 size model with the female average spinal alignment exhibited spine straightening from upper thoracic vertebra level and showed larger intervertebral angular displacements in the cervical spine than the one with the male average spinal alignment.

Conclusions: The cervical spine alignment is continuous with the thoracic spine, and a trend of the relationship between cervical spine and thoracic spinal alignment was shown in this study. Simulation results suggested that variations in thoracic spinal alignment had a potential impact on cervical spine motion as well as cervical spinal alignment in rear end impact condition.     

Prediction of cervical spine injury risk for the 6-year-old child in frontal crashes

This article presents a series of 49 km/h sled tests using the Hybrid III 6-year-old dummy in a high-back booster, a low-back booster, and a three-point belt. Although a 10-year review at a level I trauma center showed that noncontact cervical spine injuries are rare in correctly restrained booster-age children, dummy neck loads exceeded published injury thresholds in all tests. The dummy underwent extreme neck flexion during the test, causing full-face contact with the dummy's chest. These dummy kinematics were compared to the kinematics of a 12-year-old cadaver tested in a similar impact environment. The cadaver test showed neck flexion, but also significant thoracic spinal flexion which was nonexistent in the dummy. This comparison was expanded using MADYMO simulations in which the thoracic spinal stiffness of the dummy model was decreased to give a more biofidelic kinematic response. We conclude that the stiff thoracic spine of the dummy results in high neck forces and moments that are not representative of the true injury potential.     

Intervertebral neck injury criterion for prediction of multiplanar cervical spine injury due to side impacts

OBJECTIVE: Intervertebral Neck Injury Criterion (IV-NIC) is based on the hypothesis that dynamic three-dimensional intervertebral motion beyond physiological limits may cause multiplanar injury of cervical spine soft tissues. Goals of this study, using a biofidelic whole human cervical spine model with muscle force replication and surrogate head in simulated side impacts, were to correlate IV-NIC with multiplanar injury and determine IV-NIC injury threshold for each intervertebral level. METHODS: Using a bench-top apparatus, side impacts were simulated at 3.5, 5, 6.5, and 8 g horizontal accelerations of the T1 vertebra. Pre- and post-impact flexibility testing in three-motion planes measured the soft tissue injury, i.e., significant increase (p < 0.05) in neutral zone (NZ) or range of motion (RoM) at any intervertebral level, above corresponding physiological limit. RESULTS: IV-NIC in left lateral bending correlated well with total lateral bending RoM (R = 0.61, P < 0.001) and NZ (R = 0.55, P < 0.001). Additionally, the same IV-NIC correlated well with left axial rotation RoM (R = 0.50, P < 0.001). IV-NIC injury thresholds (95% confidence limits) varied among intervertebral levels and ranged between 1.5 (0.6-2.4) at C3-C4 and 4.0 (2.4-5.7) at C7-T1. IV-NIC injury threshold times were attained beginning at 84.5 ms following impact. CONCLUSIONS: Present results suggest that IV-NIC is an effective tool for determining multiplanar soft tissue neck injuries by identifying the intervertebral level, mode, time, and severity of injury.     

Influence of the Anterior and Middle Cranial Fossae on Brain Kinematics During Sagittal Plane Head Rotation

A 2D physical model of the human head was used to investigate how the irregular skull base structure affects brain kinematics during sagittal plane head dynamics. The model consisted of a rigid skull vessel with interchangeable skull base structures. One version of the model used a skull base mimicking the irregular geometry of the human. A second version used a skull base structure approximating the anterior and middle fossae as a flat surface. Silicone gel simulated the brain and was separated from the vessel by a paraffin layer which provided a slip condition at the interface between the gel and vessel. The model was exposed to 7600 rad/s² peak rotational acceleration with 6 ms pulse duration and 5° forced rotation. After 90° free rotation, the model was decelerated during 30 ms. Five repeated tests were conducted with each version. Rigid body displacement, shear strain and principal strains were determined from high-speed video recorded trajectories of grid markers located at different positions in the surrogate brain. The humanlike skull base reduced peak displacements of the inferior surfaces of the temporal and frontal lobes up to 87% and 48%, respectively. Up to 48% and 36% higher peak strains were obtained in the frontal and superior regions of the surrogate brain in the version containing the humanlike skull base. In contrast, the humanlike skull base decreased peak strain up to 28% in the central region of the surrogate brain. The results indicate that the irregular skull base offers natural protection of nerves and vessels passing through fissures and foramina in the cranial floor but also that it affects kinematics in different regions throughout the cerebrum. Implications of these results are discussed with respect to brain injury and modeling of head impact.     

Parametric analysis of vehicle design influence on the four phases of whiplash motion

OBJECTIVE: The objective is to establish a basis for motor vehicle test requirements that measure component contributions to Whiplash Associated Disorders (WAD). METHODS: Selected vehicle design features are evaluated with regard to their relative contributions to WAD measures. The motion of the occupant cervical spine associated with WAD is divided into four phases: retraction, extension, rebound, and protraction. Injury measures from the literature (NIC, extension moment, N(km), and flexion moment) represent the injury potential during each of these phases. Four vehicle design factors that affect WAD motion (vehicle stiffness, seat stiffness, head restraint height and head restraint backset) were evaluated for their contributions to the injury measures. A detailed 50th percentile male model with a biofidelic neck was used in a 100-run Monte Carlo analysis of a rear impact, varying the design factors across the values documented in the literature. Total energy was held constant and Delta V was 10 kph. RESULTS: Vehicle stiffness has a strong influence on the retraction (70%), rebound (43%), and protraction (47%) phases. Headrest backset demonstrates a strong influence on the extension (49%) and rebound (39%) phases. CONCLUSIONS: For WAD protection rating, the vehicle should be viewed as a system whereby the complex interactions among the vehicle, seat, and occupant characteristics all contribute to the WAD potential.     

Analysis of rider and child pillion passenger kinematics along with injury mechanisms during motorcycle crash

Abstract

Objective: Traffic fatalities among motorcycle users are intolerably high in Thailand. They account for 73% of the total number of road fatalities. Children are also among these victims. To improve countermeasures and design of protection equipment, understanding the biomechanics of motorcycle users under impact conditions is necessary. The objective of this work is to analyze the overall kinematics and injuries sustained by riders and child pillion passengers in various accident configurations.

Methods: Motorcycle accident data were analyzed. Common accident scenarios and impact parameters were identified. Two numerical approaches were employed. The multibody model was validated with a motorcycle crash test and used to generate possible accident cases for various impact conditions specified to cover all common accident scenarios. Specific impact conditions were selected for detailed finite element analysis. The finite element simulations of motorcycle-to-car collisions were conducted to provide insight into kinematics and injury mechanisms.

Results: Global kinematics found when the motorcycle’s front wheel impacts a car (config-MC) highlighted the translation motion of both the rider and passenger toward the impact position. The rider’s trunk impacted the handlebar and the head either impacted the car or missed. The hood constituted the highest head impact occurrence for this configuration. The child mostly impacted the rider’s back. Different kinematics were found when car impacted the lateral side of the motorcycle (config-CM). Upper bodies of both rider and child were laterally projected toward the car front. The windshield constituted the highest proportion of head impacts. The hood and A-pillar recorded a moderate proportion. The rider in finite element simulations with config-MC experienced high rib stress, lung strain, and pressure beyond the injury limit. A high head injury criterion was observed when the head hit the car. However, the simulation with config-CM exhibited high lower extremities stress and lung pressure in both occupants. Hyperextension of the rider’s neck was observed. The cumulative strain damage measure of the child’s brain was higher than the threshold for diffuse axonal injury (DAI).

Conclusions: This study revealed 2 kinematics patterns and injury mechanisms. Simulations with config-MC manifested a high risk of head and thorax injury to the rider but a low risk of severe injury to the child. Thorax injury to the rider due to handlebar impact was only found in simulations with config-MC. However, a high risk of skull, lower extremity, brain, and neck injuries were more pronounced for cases with config-CM. A high risk of DAI was also noticed for the child. In simulations with config-CM the child exhibited a higher risk of severe injury.     

Force and acceleration corridors from lateral head impact

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

The human cervical spine in tension: effects of frame and fixation compliance on structural responses

There is little data available on the responses of the human cervical spine to tensile loading. Such tests are mechanistically and technically challenging due to the variety of end conditions that need to be imposed and the difficulty of strong specimen fixation. As a result, spine specimens need to be tested using fairly complex, and potentially compliant, apparati in order to fully characterize the mechanical responses of each specimen. This, combined with the relatively high stiffness of human spine specimens, can result in errors in stiffness calculations. In this study, 18 specimen preparations were tested in tension. Tests were performed on whole cervical spines and on spine segments. On average, the linear stiffness of the segment preparations was 257 N/mm, and the stiffness of the whole cervical spine was 48 N/mm. The test frame was found to have a stiffness of 933 N/mm. Assembling a whole spine from a series combination of eight segments with a stiffness of 257 N/mm results in an estimated whole spine stiffness of 32.1 N/mm (32% error). The segment stiffnesses were corrected by assuming that the segment preparation stiffness is a series combination of the stiffnesses of the segment and the frame. This resulted in an average corrected segment stiffness of 356 N/mm. Taking the frame compliance into account, the whole spine stiffness is 51 N/mm. A series combination of eight segments using the corrected stiffnesses results in an estimated whole spine stiffness of 45.0 N/mm (12% error). We report both linear and nonlinear stiffness models for male spines and conclude that the compliance of the frame and the fixation must be quantified in all tension studies of spinal segments. Further, reported stiffness should be adjusted to account for frame and fixation compliance.     

The Contribution of Pre-impact Posture on Restrained Occupant Finite Element Model Response in Frontal Impact

Objective: The objective of this study was to discuss the influence of the pre-impact posture to the response of a finite element human body model (HBM) in frontal impacts.

Methods: This study uses previously published cadaveric tests (PMHS), which measured six realistic pre-impact postures. Seven postured models were created from the THUMS occupant model (v4.0): one matching the standard UMTRI driving posture as it was the target posture in the experiments, and six matching the measured pre-impact postures. The same measurements as those obtained during the cadaveric tests were calculated from the simulations, and biofidelity metrics based on signals correlation (CORA) were established to compare the response of the seven models to the experiments.

Results: The HBM responses showed good agreement with the PMHS responses for the reaction forces (CORA = 0.80 ± 0.05) and the kinematics of the lower part of the torso but only fair correlation was found with the head, the upper spine, rib strains (CORA= 0.50 ± 0.05) and chest deflections (CORA = 0.67 ± 0.08). All models sustained rib fractures, sternal fracture and clavicle fracture. The average number of rib fractures for all the models was 5.3 ± 1.0, lower than in the experiments (10.8 ± 9.0).

Variation in pre-impact posture greatly altered the time histories of the reaction forces, deflections and the rib strains, mainly in terms of time delay, but no definite improvement in HBM response or injury prediction was observed. By modifying only the posture of the HBM, the variability in the impact response was found to be equivalent to that observed in the experiments. The postured HBM sustained from 4 to 8 rib fractures, confirming that the pre-impact posture influenced the injury outcome predicted by the simulation.

Conclusions: This study tries to answer an important question: what is the effect of occupant posture on kinematics and kinetics. Significant differences in kinematics observed between HBM and PMHS suggesting more coupling between the pelvis and the spine for the models which makes the model response very sensitive to any variation in the spine posture. Consequently, the findings observed for the HBM cannot be extended to PMHS. Besides, pre-impact posture should be carefully quantified during experiments and the evaluation of HBM should take into account the variation in the predicted impact response due to the variation in the model posture.