The influence of seat-back and head-restraint properties on the head-neck motion during rear-impact

Transition of deformation modes from bending to auxetic compression in origami-based metamaterials for head protection from impact

For the protection of the human head by energy absorption structures, a soft mechanical response upon contact with the head is required to mitigate the effect of impact, while a hard mechanical response for highly efficient energy absorption is required to stop the movement of the head. This study realized the opposite mechanical properties during head protection by transitioning the deformation mode from bending to auxetic compression. First, non-linear finite element (FE) models were constructed to numerically reproduce the bending behavior. The calculated force responses agreed well with forces in bending tests. Using the FE models, the EA structures with proper transition of deformation modes were designed and installed in the seat headrests of real vehicles. Head protection was evaluated by dynamic loading in sled testing, in which the force on the head of the crash test dummy was measured. The head injury criterion improved from 274 to 155, indicating the superior performance of the tested structures compared to that achieved by energy absorption structures based on steel plates. Moreover, the deformation of auxetic structures prevented neck bending by holding the head. These findings present new possibilities for effectively protecting the human body by mitigating impact, facilitating energy absorption, and ensuring head stability.

Factors contributing to commercial vehicle rear-end conflicts in China: A study using on-board event data recorders

INTRODUCTION

In the last 30years, China has undergone a dramatic increase in vehicle ownership and a resulting escalation in the number of road crashes. Although crash figures are decreasing today, they remain high; it is therefore important to investigate crash causation mechanisms to further improve road safety in China.

METHOD

To shed more light on the topic, naturalistic driving data was collected in Shanghai as part of the evaluation of a behavior-based safety service. The data collection included instrumenting 47 vehicles belonging to a commercial fleet with data acquisition systems. From the overall sample, 91 rear-end crash or near-crash (CNC) events, triggered by 24 drivers, were used in the analysis. The CNC were annotated by three researchers, through an expert assessment methodology based on videos and kinematic variables.

RESULTS

The results show that the main factor behind the rear-end CNC was the adoption of very small safety margins. In contrast to results from previous studies in the US, the following vehicles' drivers typically had their eyes on the road and reacted quickly in response to the evolving conflict in most events. When delayed reactions occurred, they were mainly due to driving-related visual scanning mismatches (e.g., mirror checks) rather than visual distraction. Finally, the study identified four main conflict scenarios that represent the typical development of rear-end conflicts in this data.

CONCLUSIONS

The findings of this study have several practical applications, such as informing the specifications of in-vehicle safety measures and automated driving and providing input into the design of coaching/training procedures to improve the driving habits of drivers.

Whiplash injury prevention with active head restraint

BACKGROUND

Previous epidemiological studies have observed that an initial head restraint backset greater than 10 cm is associated with a higher risk of neck injury and persistent symptoms. The objective of this study was to investigate the relation between the active head restraint position and peak neck motion using a new human model of the neck.

METHODS

The model consisted of an osteoligamentous neck specimen mounted to the torso of a rear impact dummy and carrying an anthropometric head stabilized with muscle force replication. Rear impacts (7.1 and 11.1g) were simulated with and without the active head restraint. Physiologic rotation was determined from intact flexibility tests. Significant reductions (P<0.05) in the spinal motion peaks with the active head restraint, as compared to without, were identified. Linear regression analyses identified correlation between head restraint backset and peak spinal rotations (R(2)>0.3 and P<0.001).

FINDINGS

The active head restraint significantly reduced the average peak spinal rotations, however, these peaks exceeded the physiologic range in flexion at head/C1 and in extension at C4/5 through C7/T1. Correlation was observed between the head restraint backset and the extension peaks at C4/5 and C5/6.

INTERPRETATION

Correlation between head restraint backset and spinal rotation peaks indicated that a head restraint backset in excess of 8.0 cm may cause hyperextension injuries at the middle and lower cervical spine. The active head restraint may not be fully activated at the time of peak spinal motions, thus reducing its potential protective effects.

Deceleration during 'real life' motor vehicle collisions - a sensitive predictor for the risk of sustaining a cervical spine injury?

Background

The predictive value of trauma impact for the severity of whiplash injuries has mainly been investigated in sled- and crash-test studies. However, very little data exist for real-life accidents. Therefore, the predictive value of the trauma impact as assessed by the change in velocity of the car due to the collision (ΔV) for the resulting cervical spine injuries were investigated in 57 cases after real-life car accidents.

Methods

ΔV was determined for every car and clinical findings related to the cervical spine were assessed and classified according to the Quebec Task Force (QTF).

Results

In our study, 32 (56%) subjects did not complain about symptoms and were therefore classified as QTF grade 0; 25 (44%) patients complained of neck pain: 8 (14%) were classified as QTF grade I, 6 (10%) as QTF grade II, and 11 (19%) as QTF grade IV. Only a slight correlation (r = 0.55) was found between the reported pain and ΔV. No relevant correlation was found between ΔV and the neck disability index (r = 0.46) and between ΔV and the QTF grade (r = 0.45) for any of the collision types. There was no ΔV threshold associated with acceptable sensitivity and specificity for the prognosis of a cervical spine injury.

Conclusion

The results of this study indicate that ΔV is not a conclusive predictor for cervical spine injury in real-life motor vehicle accidents. This is of importance for surgeons involved in medicolegal expertise jobs as well as patients who suffer from whiplash-associated disorders (WADs) after motor vehicle accidents.

Trial registration

The study complied with applicable German law and with the principles of the Helsinki Declaration and was approved by the institutional ethics commission.

Influence of anthropometry on the kinematics of the cervical spine and the risk of injury in sled tests in female volunteers

The objective of this study was to investigate the influence of anthropometric data on the kinematics of the cervical spine and the risk factors for sustaining a neck injury during rear-end collisions occurring in a sled test. A rear-end collision with a velocity change (DeltaV) of 6.3 km/h was simulated in a sled test with eight healthy female subjects. The study analysed the association of anthropometric data with the initial distance between the head and the head restraint, defined kinematic characteristics, the neck injury criterion (NIC) and the neck injury criterion minor (NICmin). The head circumference is negatively associated (r=-0.598) with the initial distance between the head and the head restraint, the maximal head extension (r=-0.687) and the maximal dorsal angular head acceleration (r=-0.633). The body weight (r=0.800), body height (r=0.949) and thorax circumference (r=0.632) are positively associated with the maximal ventral head translation. The neck length correlates positively with the NIC (r=0.826) and negatively with the NICmin (r=-0.797). Anthropometric factors influence the kinematics of the cervical spine and the risk of injury. A high risk of injury may be assumed for individuals with a small head circumference, long neck, tall body height and high body weight.

Influence of seat geometry and seating posture on NIC(max) long-term AIS 1 neck injury predictability

OBJECTIVE

Validated injury criteria are essential when developing restraints for AIS 1 neck injuries, which should protect occupants in a variety of crash situations. Such criteria have been proposed and attempts have been made to validate or disprove these. However, no criterion has yet been fully validated. The objective of this study is to evaluate the influence of seat geometry and seating posture on the NIC(max) long-term AIS 1 neck injury predictability by making parameter analyses on reconstructed real-life rear-end crashes with known injury outcomes.

METHODS

Mathematical models of the BioRID II and three car seats were used to reconstruct 79 rear-end crashes involving 110 occupants with known injury outcomes. Correlations between the NIC(max) values and the duration of AIS 1 neck injuries were evaluated for variations in seat geometry and seating posture. Sensitivities, specificities, positive predictive values, and negative predictive values were also calculated to evaluate the NIC(max) predictability.

RESULTS

Correlations between the NIC(max) values and the duration of AIS 1 neck injuries were found and these relations were used to establish injury risk curves for variations in seat geometry and seating posture. Sensitivities, specificities, positive predictive values, and negative predictive values showed that the NIC(max) predicts long-term AIS 1 neck injuries also for variations in seat geometry and seating postures.

CONCLUSION

The NIC(max) can be used to predict long-term AIS 1 neck injuries.

Effect of head restraint backset on head-neck kinematics in whiplash

Although head restraints were introduced in the 1960s as a countermeasure for whiplash, their limited effectiveness has been attributed to incorrect positioning. The effect of backset on cervical segmental angulations, which were previously correlated with spinal injury, has not been delineated. Therefore, the practical restraint position to minimize injury remains unclear. A parametric study of increasing head restraint backset between 0 and 140mm was conducted using a comprehensively validated computational model. Head retraction values increased with increasing backset, reaching a maximum value of 53.5mm for backsets greater than 60mm. Segmental angulation magnitudes, greatest at levels C5-C6 and C6-C7, reached maximum values during the retraction phase and increased with increasing backset. Results were compared to a previously published head restraint rating system, wherein lower cervical extension magnitudes from this study exceeded mean physiologic limits for restraint positions rated good, acceptable, marginal, and poor. As head restraint contact was the limiting factor in head retraction and segmental angulations, the present study indicates that minimizing whiplash injury may be accomplished by limiting head restraint backset to less than 60mm either passively or actively after impact.

Variability in vehicle and dummy responses in rear-end collisions

OBJECTIVE

The objective of this study was to quantify the occupant response variability due to differences in vehicle and seat design in low-speed rear-end collisions.

METHODS

Occupant response variability was quantified using a BioRID dummy exposed to rear-end collisions in 20 different vehicles. Vehicles were rolled rearward into a rigid barrier at 8 km/h and the dynamic responses of the vehicle and dummy were measured with the head restraint adjusted to the up most position. In vehicles not damaged by this collision, additional tests were conducted with the head restraint down and at different impact speeds.

RESULTS

Despite a coefficient of variation (COV) of less than 2% for the impact speed of the initial 8 km/h tests, the vehicle response parameters (speed change, acceleration, restitution, bumper force) had COVs of 7 to 23% and the dummy response parameters (head and T1 kinematics, neck loads, NIC, N(ij) and N(km)) had COVs of 14 to 52%. In five vehicles tested multiple times, a head restraint in the down position significantly increased the peak magnitude of many dummy kinematic and kinetic response parameters. Peak head kinematics and neck kinetics generally varied linearly with head restraint back set and height, although the neck reaction moment reversed and increased considerably if the dummy's head wrapped onto the top of the head restraint.

CONCLUSIONS

The results of this study support the proposition that the vehicle, seat, and head restraint are a safety system and that the design of vehicle bumpers and seats/head restraint should be considered together to maximize the potential reduction in whiplash injuries.

Assessing automobile head restraint positioning in Portland, Oregon

OBJECTIVE

Automobile head restraints, when used properly, have been shown to decrease the incidence and severity of whiplash injuries to the neck. Before the development of a public campaign on proper head restraint positioning, the authors assessed head restraint positioning and public understanding.

DESIGN

Over a one month period, the position of the vehicle head restraint of drivers was observed in moving cars in the city of Portland, Oregon (population 530,000). Optimal position was defined as having the head restraint above the ears with the back of the head touching the head restraint. A questionnaire on head restraint understanding was administered to people during jury service.

RESULTS

Of the 4287 drivers observed, 1% (n = 30) had no head restraint on their seat, 4% (n = 158) had a fixed head restraint, and 95% (n = 4099) had an adjustable head restraint. Among the fixed head restraints, 21% (33/158) were positioned optimally with no horizontal gap. Among the adjustable head restraints, only 7% (280/4099) had optimal head restraint positioning. Overall, 93% (3974/4287) of all head restraints observed were suboptimally positioned. Seventy five percent (38/51) of polled Portland residents identified safety as the primary head restraint function.

CONCLUSION

Ninety three percent of all head restraints observed were suboptimally positioned. Fixed head restraints were three times more likely to be in optimal position than adjustable head restraints (21% v 7%). Most polled Portland residents understood the proper function and positioning of head restraints. This discrepancy between actual practice and understanding should be addressed with public education and manufacturer design changes.

Biofidelic whole cervical spine model with muscle force replication for whiplash simulation

Whiplash has been simulated using volunteers, whole cadavers, mathematical models, anthropometric test dummies, and whole cervical spines. Many previous in vitro whiplash models lack dynamic biofidelity. The goals of this study were to (1) develop a new dynamic whole cervical spine whiplash model that will incorporate anterior, lateral and posterior muscle force replication, (2) evaluate its performance experimentally and (3) compare the results with in vivo data. To evaluate the new model, rear-impact whiplash simulations were performed using the incremental trauma approach at maximum measured T1 horizontal accelerations of 3.6 g, 4.7 g, 6.6 g, and 7.9 g. The kinematic response of the new model, e.g., peak head-T1 extension and peak intervertebral rotations, were compared with the corresponding in vivo data. The average peak head-T1 extension was within the in vivo corridor during the 3.6 g whiplash simulation (9.1 kph delta V). The peak in vivo intervertebral rotations obtained during a 4.6 g whiplash simulation of a young volunteer were within, or only marginally in excess of, the 95% confidence limits of the average peak intervertebral rotations measured during the 4.7 g whiplash simulation of the present study. Thus, the new whole cervical spine model with muscle force replication produced biofidelic dynamic responses to simulated whiplash. The new model is capable of generating important biomechanical data that may help improve our understanding of whiplash injuries and injury mechanisms.

The effect of collision pulse properties on seven proposed whiplash injury criteria

Recent epidemiological and biomechanical studies have suggested that whiplash injury is related to a vehicle's average acceleration rather than its speed change during a rear-end collision. To further explore this phenomenon, the effect of various kinematic properties of the collision pulse on seven proposed whiplash injury criteria was quantified. A BioRID II rear-impact dummy was seated on a programmable sled and exposed six times to each of 15 different collision pulses. Five properties of the collision pulse were varied: peak acceleration (1.3-4.4 g), speed change (3-11 km/h), duration (52-180 ms), displacement (2-26 cm) and shape (square, sine and triangular). Linear and angular accelerations and displacements of the head, and linear accelerations of the T1 and pelvis were measured in the sagittal-plane. Upper neck loads in the sagittal-plane were also measured. Variations within the proposed injury criteria between the different pulses were compared using analyses of variance. Six criteria--peak upper neck shear force, peak upper neck moment, peak retraction, the neck injury criterion (NIC) and two normalized neck injury criteria (Nij and Nkm)--exhibited graded responses that were most sensitive to the average acceleration of the collision pulse. Peak extension angle between the head and T1 decreased with both increasing speed change and peak acceleration, and was, therefore, deemed unsuitable as a whiplash injury criterion for the BioRID dummy. Of the seven criteria, Nij and Nkm were best able to distinguish between the 15 pulses. If the six graded injury criteria are related to the risk of whiplash injury, then the results of this study indicate that the risk of whiplash injury can be reduced by bumper and seat designs that prolong the collision pulse and thereby reduce the average vehicle and occupant accelerations for a given speed change.

The relationship between clinical and kinematic responses from human subject testing in rear-end automobile collisions

Recent experiments have produced a linked data set of clinical and kinematic responses for human subjects exposed to controlled low-speed rear-end collisions. The purpose of this paper was to examine this paired data set and determine whether the presence or absence of clinical symptoms could be predicted from the peak linear and angular kinematic response of the head and neck. The data were generated using 42 male and female human subjects seated normally in the front passenger seat of a stationary vehicle struck from behind to produce vehicle speed changes of 4 and 8 km/h. Pre- and post-test clinical examinations documented the presence, severity and duration of whiplash-associated disorders (WAD). Logistic regression and backward elimination of independent variables were used to develop the prediction model. The analysis yielded a 16 parameter model that was significantly related (odds ratio = 21.2; P = 0.0069) to the presence or absence of transient whiplash symptoms. The model correctly predicted symptom presence in 13 of 23 tests (sensitivity 57%) and symptom absence in 49 of 52 tests (specificity 94%) in a population of 75 with a symptom prevalence of 31%. The model's positive predictive value was 81% and its negative predictive value was 83%. Despite statistical significance, the model did not discriminate between the presence and absence of symptoms in all tests, and indicated that factors other than the selected peak kinematic responses influenced symptom production.

Seat back and head restraint response during low-speed rear-end automobile collisions

Automobile seat backs and head restraints play a key safety role during low-speed rear-end collisions, yet few studies have explored the effect of collision variables on seat response. In this study, the effects of vehicle speed change and seat belt use on dynamic seat back and head restraint response during low-speed rear-end automobile collisions were examined. Four human subjects were repeatedly exposed to vehicle-to-vehicle rear-end collisions with speed changes of 2, 4, 6 and 8 km/h. Seat back force and deflection, and head restraint force were measured. The point of application of the resultant force applied to the seat back and head restraint were determined. The magnitude and time of peak kinematic and kinetic response parameters were used in a two-way repeated-measures analysis of variance (ANOVA) for speed change and seat belt use. The results showed that 20 of the 24 seat back and head restraint response parameters varied with speed change and none of the parameters varied with seat belt use. Head restraint forces, seat back forces and seat back deflections increased approximately linearly with speed change, whereas time to peak response, direction and moment arm of the forces remained either constant or varied only slightly over the range of speed changes tested.

The influence of head restraint and occupant factors on peak head/neck kinematics in low-speed rear-end collisions

Prior two-way analyses of variance showed that the peak kinematic response of the head and neck of subjects exposed to low-speed rear-end collisions was related to speed change and gender, however potential reasons for this gender dependence were not determined. Using multiple linear regression, this study further examined these response data to determine the relative influence of specific factors, including subject anthropometry, neck strength, cervical range of motion, seated posture and head restraint position, which may have been responsible for the previously-observed gender dependence. The results of this analysis showed that vehicle speed change and relative head restraint position explained the largest proportion of the observed variation in peak occupant kinematic response. Seated posture measures also explained some of the variation in kinematic response. The current analysis prioritizes which variables to explore more thoroughly in future research and which variables should be carefully controlled in future studies.

Sick leave and disability pension among passenger car occupants injured in urban traffic

STUDY DESIGN

A follow-up cohort study of passenger car occupants injured in car crashes in an urban area in Sweden.

OBJECTIVES

To analyze the injuries, injury events, and long-term consequences of injuries in car crashes.

SUMMARY OF BACKGROUND DATA

The consequences of car crashes usually are described in terms of the number of people injured, the severity of injuries, or the number of inpatient days. Certain types of crash injuries can results in long-term sick leave and granting of disability pension. The increased socioeconomic significance of these outcomes is not always indicated by analysis of commonly used variables.

METHODS

Two hundred fifty-five passenger car occupants aged 16-64 years who were injured in car crashes in urban traffic were analyzed in terms of length of sick leave and receipt of disability pension.

RESULTS

Strain of the cervical spine was the most common type of injury (55%, 141 injuries), and these injuries accounted for 82% of all sick leave taken within 2.5 years after the injury event. Injury to the cervical spine in 16 of 18 cases resulted in long-term sick leave or dependence on disability pension. The most common injury mechanism was rear-end collisions (39%). This type of crash resulted in 64% of all sick-leave days within 2.5 years after the injury event. Twelve out of 18 injured people on long-term sick leave or receiving disability pension had been in cars struck from behind.

CONCLUSIONS

It is important to include long-term consequences in the form of sick leave and disability pension when describing the consequences of different types of car crashes and injuries.