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The objective of this study was to assess the biomechanical and kinematic responses of female volunteers with two different head restraint (HR) configurations when exposed to a low-speed rear loading environment. A series of rear impact sled tests comprising eight belted, near 50th percentile female volunteers, seated on a simplified laboratory seat, was performed with a mean sled acceleration of 2.1 g and a velocity change of 6.8 km/h. Each volunteer underwent two tests; the first test configuration, HR10, was performed at the initial HR distance ∼10 cm and the second test configuration, HR15, was performed at ∼15 cm. Time histories, peak values and their timing were derived from accelerometer data and video analysis, and response corridors were also generated. The results were separated into three different categories, HR10C (N = 8), HR15C (N = 6), and HR15NC (N = 2), based on: (1) the targeted initial HR distance [10 cm or 15 cm] and (2) whether the volunteers’ head had made contact with the HR [Contact (C) or No Contact (NC)] during the test event. The results in the three categories deviated significantly. The greatest differences were found for the average peak head angular displacements, ranging from 10° to 64°. Furthermore, the average neck injury criteria (NIC) value was 22% lower in HR10C (3.9 m2/s2), and 49% greater in HR15NC (7.4 m2/s2) in comparison to HR15C (5.0 m2/s2). This study supplies new data suitable for validation of mechanical or mathematical models of a 50th percentile female. A model of a 50th percentile female remains to be developed and is urgently required to complement the average male models to enhance equality in safety assessments. Hence, it is important that future protection systems are developed and evaluated with female properties taken into consideration too. It is likely that the HR15 test configuration is close to the limit for avoiding HR contact for this specific seat setup. Using both datasets (HR15C and HR15NC), each with its corresponding HR contact condition, will be possible in future dummy or model evaluation.

“Whiplash Injury” describes those injury deriving from the sharp whipping movement of both head andneck, produced at the moment of a traffic accident, particularly following collision from behind, head-on orside collisions. The use of safety belts has led to a reduction in deaths deriving from front-end collisions, butalso to an increase in cases of typical whiplash. There are two types of forces that cause whiplash injuries inrear-end car crashes: external forces applied to the body by the seat and head restraint, and internal forcesgenerated by the activation of body’s muscles. The combination of these forces causes differential motion ofthe cervical spine, which results in neck tissues’ strain. This event can affect all neck structures: facet jointscapsule, muscles, intervertebral disks, nerves and vessels. We report a case of a 68-year-old woman. Thesubject, while driving her car, hit head-on a car moving in the opposite direction and died immediately. Atautopsy the major findings were limited to multiple rib fractures and fracture of the fifth cervical vertebrawith epidural hematoma. This case demonstrates that, even in the absence of direct traumatism, a potentiallylethal epidural hematoma may occur as a result of whiplash.

Car seat design has gained extensive importance considering comfort and safety where it interacts with the human anthropometry. In the majority of car accidents, it is the car seat design and the design of the associated safety accessories that prevent damage to the driver’s body. Head restraint saves the passenger from Whiplash injuries due to sudden impact that may be fatal. Head restraint’s primary function is to support the head and keep the head in position with the torso in case of sudden impacts. In this paper, the importance of head restraint is justified by applying dynamic analysis to the head and torso model developed by solid modeling software considering the anthropometry of the Indian population. Anthropometry is crucial for design consideration so that the design conforms near to the ideal design which would accommodate the majority of the populace. The head restraint that is not designed considering anthropometry would leave many individuals at a disadvantage of safety issues that a car design promises. Ergonomics of the head restraint is important to arrest the undesired head movement. This paper presents the analysis of the current commonly used car seat’s head restraint design in various ratings of good, acceptable, marginal, and poor according to Indian anthropometry.

Whiplash injuries are one of the most common injuries reported in automotive rear end collisions. Automobile seat back and head restraints play a role in reducing neck injuries during low speed rear end collisions. Currently, many studies are being conducted on ways to reduce neck injuries. These deal with the design parameters that cause neck injuries and do not address the design of the head restraint connection structure. In this paper, we analyze the various trajectories of the headrest and propose a new design for a connection structure that can move along the corresponding trajectory. We model the headrest connection mechanism as a virtual link using kinematic modeling and perform trajectory analysis. Using the trajectory of motion, we select an oblong shape for the guide slot by fitting it with the equation of an ellipse and propose a new headrest connection mechanism. To evaluate the design of the proposed mechanism, we model the shape of the mechanism and test it using dynamic simulation under collision conditions. In addition, we design a prototype for the proposed guide, conduct a sled test, and confirm that the neck force is reduced by the proposed connection structure. In the proposed structure, the values of maximum upper neck shear and tension decreased by more than 20 % compared to existing headrest.

Current neck injury criteria used to evaluate whiplash injuries are based on the kinematics or kinetics of the occupant’s head and neck during rear impacts. The occupant’s response is affected by many factors including impact severity, seat design and occupant related factors such as gender and posture. Most of the current finite element models are concerned with modeling the head and neck, ignoring the interaction of the seat with the occupant during rear collision. In this work the Global Human Body Model Consortium (GHBMC) finite element model was used to study these interaction effects with emphases on the effect of seat belt, headrest and seat stiffness on the occupant’s response during rear-end collisions and evaluate the response using three neck injury criteria. The study shows the dramatic importance of the occupant’s seat restraint and head rest upon occupant safety. Specifically, the occupant ramping during rear impacts can be prevented by using the seat belt. Furthermore, the headrest reduces the head displacement and rotation. Our work further reveals that the head displacement reduction can lead to higher moments, axial and shear forces at the neck, especially for cases involving poorly adjusted or stiffer headrest.

Head restraint systems specifically engineered to reduce the impact of whiplash injury in the event of a rear-end collision were introduced in the late 1990s with the aim of reducing whiplash injury risk that went 'beyond simple geometric improvements' to head restraints. Whilst studies have shown that whiplash-reducing head restraint systems are highly effective in reducing whiplash injury, these were based on a limited range of systems including Toyota's Whiplash Injury Lessening (WIL) seating system, Volvo's Whiplash Injury Prevention System (WHIPS) and the Saab Active Head Restraint (SAHR) and have generally focussed on Swedish crash and insurance data. However, there has been no broad real-world crash-based evaluation of the effectiveness of whiplash-reducing head restraint systems currently present in the vehicle fleet that validates the results of these studies in other populations. The objective of this study was to undertake a retrospective evaluation of vehicle whiplash-reducing head restraint systems to prevent whiplash injury using real-world crash data linked to insurance claims data in Victoria, Australia. It was found that whiplash-reducing head restraint systems are associated with a statistically significant reduction in the odds of driver and front seat passenger whiplash injury in a vehicle struck in a rear-end collision of 11.6 % (95 % CI 0.20 %, 21.6 %). The results indicate that whiplash-reducing head restraint systems are an effective technology for reducing the risk of whiplash injury to drivers and front seat passengers in a vehicle struck in a rear-end collision. Considering that around a quarter of all casualty crashes involving passenger and light commercial vehicles are rear-end, the fitment of whiplash-reducing head restraint systems to all vehicles as a standard safety feature would likely see a significant reduction in the incidence of whiplash injury.

Synopsis Head and spinal injuries commonly occur during motor vehicle crashes (MVCs). The goal of this clinical commentary is to discuss real-life versus simulated MVCs and to present clinical, biomechanical, and epidemiological evidence of MVC-related injury mechanisms. It will also address how this knowledge may guide and inform the design of injury mitigation devices and assist in clinical decision making. Evidence indicates that there exists no universal injury tolerance applicable to the entire population of the occupants of MVCs. Injuries sustained by occupants depend on a number of factors, including occupant characteristics (age, height, weight, sex, bone mineral density, and pre-existing medical and musculoskeletal conditions), pre-MVC factors (awareness of the impending crash, occupant position, usage of and position of the seatbelt and head restraint, and vehicle specifications), and MVC-related factors (crash orientation, vehicle dynamics, type of active or passive safety systems, and occupant kinematic response). Injuries resulting from an MVC occur due to blunt impact and/or inertial loading. An S-shaped curvature of the cervical spine and associated injurious strains have been documented during rear-, frontal-, and side-impact MVCs. Data on the injury mechanism and the quantification of spinal instability guide and inform the emergent and subsequent conservative or surgical care. Such care may require determining optimal patient positioning during transport, which injuries may be treated conservatively, whether reduction should be performed, optimal patient positioning intraoperatively, and whether bracing should be worn prior to and/or following surgery. The continued improvement of traditional injury mitigation systems, such as seats, seatbelts, airbags, and head restraints, together with research of newer collision-avoidance technologies, will lead to safer motor vehicles and ultimately more effective injury management strategies. J Orthop Sports Phys Ther 2016;46(10):826-833. Epub 3 Sep 2016. doi:10.2519/jospt.2016.6716.

Objective: Whiplash-associated disorder (WAD), commonly denoted whiplash injury, is a worldwide problem. These injuries occur at relatively low changes of velocity (typically Methods: The seated positions of drivers in stationary conditions have been investigated in a total of 76 volunteers (34 females, 42 males) who participated in the study. Inclusion criteria incorporated driving a Saab 9–3 on a regularly basis. Results: The majority of the volunteers (89%) adjusted the head restraint to any of the 3 uppermost positions and as many as 59% in the top position. The average vertical distance between the top of the head and the top of the head restraint (offset) increase linearly with increasing statures, from an average of −26 mm (head below the head restraint) for small females to an average of 82 mm (head above the head restraint) for large males. On average, the offset was 23 mm for females, which is within a satisfactory range and in accordance with recommendations; the corresponding value for males was 72 mm. The backset tended to be shorter among female volunteers (on average 27 mm) compared to the male volunteers (on average 44 mm). Moreover, the backset tended to increase with increasing statures. Conclusions: Incorrect adjustment of the head restraint cannot explain the large differences found between the sexes in the effectiveness of the SAHR system.

Objectives: The Insurance Institute for Highway Safety (IIHS) rates front seat/head restraint designs using a combination of static and dynamic measurements following RCAR-IIWPG procedures. The purpose of this study was to determine whether vehicles with better IIHS-rated seats/head restraints had lower injury risk in rear-end collisions and how the effect of better rated seats interacted with driver gender and age. Methods: The presence of an associated insurance injury claim was determined for rear-impact crashes using 2001–2014 model year cars and SUVs. Logistic regression was used to compare injury risk for vehicles with good, acceptable, and marginal IIHS-rated seats/head restraints with poor-rated seats/head restraints. Analyses were run by gender and driver age and also by the rate of more severe injury claims. Results: Injury rates were 11.2% lower for vehicles with seats/head restraints rated good compared to vehicles with seats/head restraints rated poor. The percentage reduction for good- versus poor-rated seats was greater for females (12.7%) than males (8.9%). Comparing good- with poor-rated seats, driver ages 15–24 had the largest reduction at 19.8%, followed by 10.7% for driver ages 45–64 and 10.4% for driver ages 25–44. Conclusions: Seats/head restraints with better IIHS ratings are associated with lower injury rates in rear-impact collisions than seats rated poor. The reductions in injury rates were strongest for females and for young-to–middle-age drivers. The strong reductions in injury rates for these groups are encouraging given their high initial injury rates.

Objective: This study investigated overall performance of an energy-absorbing sliding seat concept for whiplash neck injury prevention. The sliding seat allows its seat pan to slide backward for some distance under certain restraint force to absorb crash energy in rear impacts. Methods: A numerical model that consisted of vehicle interior, seat, seat belt, and BioRID II dummy was built in MADYMO to evaluate whiplash neck injury in rear impact. A parametric study of the effects of sliding seat parameters, including position and cushion stiffness of head restraint, seatback cushion stiffness, recliner characteristics, and especially sliding energy-absorbing (EA) restraint force, on neck injury criteria was conducted in order to compare the effectiveness of the sliding seat concept with that of other existing anti-whiplash mechanisms. Optimal sliding seat design configurations in rear crashes of different severities were obtained. A sliding seat prototype with bending of a steel strip as an EA mechanism was fabricated and tested in a sled test environment to validate the concept. The performance of the sliding seat under frontal and rollover impacts was checked to make sure the sliding mechanism did not result in any negative effects. Results: The protective effect of the sliding seat with EA restraint force is comparable to that of head restraint–based and recliner stiffness–based anti-whiplash mechanisms. EA restraint force levels of 3 kN in rear impacts of low and medium severities and 6 kN in impacts of high severity were obtained from optimization. In frontal collision and rollover, compared to the nonsliding seat, the sliding seat does not result in any negative effects on occupant protection. The sled test results of the sliding seat prototype have shown the effectiveness of the concept for reducing neck injury risks. Conclusion: As a countermeasure, the sliding seat with appropriate restraint forces can significantly reduce whiplash neck injury risk in rear impacts of low, medium, and high severities with no negative effects on other crash load cases.

A correctly positioned vehicle head restraint (HR) can reduce whiplash injury risk in collisions, however, HRs are often sub-optimally positioned. The primary aim of this study was to investigate vehicle HR position and driver knowledge of correct HR positioning in an Irish population. Secondary aims were to investigate the associations with driver age, gender and vehicle age. Data collection involved HR measurement and a driver questionnaire (n = 110). Just 27% of drivers had optimal HR positioning, while 30% had poor or marginal positioning. Newer vehicles (

Previous research indicates that most vehicle occupants are unaware that a correctly adjusted, well-designed vehicular head restraint provides substantial protection against whiplash injuries. This study examined whether a brief educational intervention could improve awareness regarding whiplash injuries and prevention strategies among a cohort of vehicle fleet managers.A brief written survey was administered prior to, and approximately 1 h after a 30-min presentation on whiplash injury and prevention measures, which was delivered at a regional fleet manager meeting held in British Columbia, Canada (n = 27 respondents).Respondents had low baseline knowledge levels regarding the causes, consequences, and prevention of whiplash. Following the presentation, however, respondents improved awareness in all of these domains and, most important, reported an increased motivation to implement changes based on this newly acquired knowledge.These results indicate that improved education practices and social marketing tools are potentially valuable to increase awareness among relevant stakeholders.

In order to solve the problem that the performance of anti-whiplash seat did not satisfy the requirements of score, the seat is analyzed for the structure and simulation. It is found that there are several main factors which have great influence on it such as Head Restraint geometry position, Head Restraint and seat back stiffness, seat bracket stiffness and so on. With optimized and adjusted correlative parameter, the seat exerts itself completely with excellent performance of anti-whiplash and this performance of car will also meet target request.

Chronic radicular symptoms have been documented in whiplash patients, potentially caused by cervical neural tissue compression during an automobile rear crash. Our goals were to determine neural space narrowing of the lower cervical spine during simulated rear crashes with whiplash protection system (WHIPS) and active head restraint (AHR) and to compare these data to those obtained with no head restraint (NHR). We extrapolated our results to determine the potential for cord, ganglion, and nerve root compression.Our model, consisting of a human neck specimen within a BioRID II crash dummy, was subjected to simulated rear crashes in a WHIPS seat (n = 6, peak 12.0 g and ΔV 11.4 kph) or AHR seat and subsequently with NHR (n = 6, peak 11.0 g and ΔV 10.2 kph with AHR; peak 11.5 g and ΔV 10.7 kph with NHR). Cervical canal and foraminal narrowing were computed and average peak values statistically compared (P0.05) between WHIPS, AHR, and NHR.Average peak canal and foramen narrowing could not be statistically differentiated between WHIPS, AHR, or NHR. Peak narrowing with WHIPS or AHR was 2.7 mm for canal diameter and 1.6 mm, 2.7 mm, and 5.9 mm(2) for foraminal width, height and area, respectively.While lower cervical spine cord compression during a rear crash is unlikely in those with normal canal diameters, our results demonstrated foraminal kinematics sufficient to compress spinal ganglia and nerve roots. Future anti-whiplash systems designed to reduce cervical neural space narrowing may lead to reduced radicular symptoms in whiplash patients.

This study presents car seat concepts which are designed to mitigate whiplash injuries through coordinated motion of seat components for a wide range of crash severities. In order to evaluate the effectiveness of the proposed car seat concepts, computational multibody models of a generic car seat and a biofidelic 50th-percentile male human model for rear impact are developed. A number of car seat concepts are shown to reduce the risk of whiplash injuries by utilizing head restraint support and energy-absorbing features, which remain reusable after impact.

To reduce whiplash injury risk in low-speed rear-impact accidents, a sliding mechanism of vehicle seat with crash energy-absorption (EA) function is proposed and analysed in this study. It can reduce relative motion between occupant head and torso under rear impact and lower values of neck injury related parameters such as neck injury criterion (NIC), neck displacement criterion (NDC) and neck forces and moment. A number of parameters of seat structure and countermeasures have great influence on occupant head–neck responses in rear impacts. They include head restraint position, seat recliner characteristic and seatback cushion stiffness, as well as the newly proposed seat sliding characteristic. A numerical model that includes a seat and a BIORID II dummy is used in a parametric study to evaluate effects of whiplash injury risk reduction. The analysis results show that proper combinations of the values of these parameters can mitigate the whiplash injuries and they form the basis of the existing counterme...

This paper evaluates the consequences of the impact of an unrestrained object against the head of vehicle occupant during a frontal crash by means of a computational head–neck biomechanical model. The correct positioning of head restraints can partially protect the rear side of the head, but there is still a significant probability of being injured. However, because head restraints are typically not properly adjusted as whiplash studies have shown, the probability of being impacted by an unrestrained object during a frontal crash is noticeably high and hence the risk of being injured is also high. In this work, head injury risk is evaluated through the Head Injury Criterion (HIC), by simulating a complete head–neck biomechanical model with realistic motion under frontal crash condition. The model developed includes all cervical vertebrae, intervertebral discs, ligaments and muscles. The model was validated against experimental data. Results have shown that the risk of severe head injury in frontal collisi...

Domestic automobile insurance claims were investigated to correlate the driver neck injury risk with the safety rating of the head restraint, the severity of vehicle damage, and other human factors. The results of our statistical analysis reveal that the risk of neck injury for the driver is significantly different for vehicle size, use, driver gender, driver age, impact direction, accident location, and safety rating of head restraint, depending on vehicle the damage level which is assumed to imply impact severity during a rear-end crash accident. One of the unique findings from domestic insurance claims from low-speed rear-end crash accidents is the frequent reports of lower back injury together with whiplash. Thus, the risk of lower back discomfort is also included in this statistical analysis.

This paper presents the validation of a 50th-percentile male multi-body human model specifically developed for rear-impact simulation. The aim is to develop a biofidelic model with the simplest architecture that can simulate the interaction of the human body with the seat during rear impact. The model was validated using the head-and-neck and torso responses of seven volunteers from the Japanese Automobile Research Institute sled tests, which were performed at an impact speed of 8km/h with a rigid seat and without head restraint and seat belt. The results indicate that the human-body model can effectively mimic the rear-impact response of a 50th-percentile male with a good level of accuracy and has the potential to predict whiplash injury.

Objectives: Whiplash injuries from vehicle collisions are common and costly. These injuries most frequently occur as a result of a rear impact and, compared to males, females have up to twice the risk of whiplash-associated disorders (WAD) resulting from vehicle crashes. The present study focuses on the differences in the dynamic response corridors of males and females in low-severity rear impacts. Methods: In this study, analysis of data fromvolunteer tests of females frompreviously published data has been performed. Corridors for the average female response were generated based on 12 volunteers exposed to a change of velocity of 4 km/h and 9 volunteers exposed to a change of velocity of 8 km/h. These corridors were compared to corridors for the average male response that were previously generated based on 11 male volunteers exposed to the same test conditions. Results: Comparison between the male and female data showed that the maximum x-acceleration of the head for the females occurred on average 10 ms earlier and was 29% higher during the 4 km/h test and 12 ms earlier and 9% higher during the 8 km/h test. Head-to-head restraint contact for the females occurred 14 ms earlier at 4 km/h and 11 ms earlier at 8 km/h compared to the males. For the same initial head-to-head restraint distance, head restraint contact occurred 11 and 7 ms earlier for the females than the males at 4 and 8 km/h, respectively. Furthermore, the calculated Neck Injury Criteria (NIC) values were similar for males and females at 4 km/h, whereas they were lower for females compared to the males at 8 km/h (3.2 and 4.0 m2/s2, respectively). Conclusions: The results of this study highlight the need to further investigate the differences in dynamic responses between males and females at low-severity impacts. Such data are fundamental for the development of future computer models and dummies for crash safety assessment. These models can be used not only as a tool in the design and development process of protective systems but also in the process of further evaluation and development of injury criteria.

This study presents an investigation of anti-whiplash features that can be implemented in a car seat to reduce whiplash injuries in the case of a rear impact. The main emphasis is on achieving a seat design with good energy absorption properties.A biofidelic 50th percentile male multi-body human model for rear impact is developed to evaluate the performance of car seat design concepts. The model is validated using the responses of 7 volunteers from the Japanese Automobile Research Institute (JARI) sled tests, which were performed at an impact speed of 8 kph with a rigid seat and without head restraint and seatbelt. A generic multi-body car seat model is also developed to implement various seatback and recliner properties, anti-whiplash devices, and head restraints. Using the same driving posture and the rigid seat in the JARI sled tests as the basic configuration, several anti-whiplash seats are designed to allow different types of motion for the seatback and seat-pan.The anti-whiplash car seat design concepts limit neck internal motion successfully until the head-to-head restraint contact occurs and they exhibit low NIC(max) values (7 m(2)/s(2) on average). They are also effective in reducing neck compression forces and T1 forward accelerations. In principle, these car seat design concepts employ controlled recliner rotation and seat-pan displacement to limit the formation of S-shape. This is accomplished by using anti-whiplash devices that absorb the crash energy in such a way that an optimum protection is provided at different severities.The results indicate that the energy absorbing car seat design concepts all demonstrate good whiplash-reducing performances at the IIWPG standard pulse. Especially in higher severity rear impacts, two of the car seat design concepts reduce the ramping of the occupant considerably.

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 (ΔV) 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.

This paper reports the design and development of a novel head restraint system for automotive applications to reduce whiplash injuries to occupants. This head restraint mechanism is combined with a pair of ultrasonic sensors, actuators and control algorithm to form an active head restraint system, which detects the position of an occupant's head when seated in the car and moves the head restraint into an optimum position to reduce the chances of receiving whiplash injuries in the event of a rear impact. The system monitors significant changes in the position of the head and moves the head restraint to the desired position. A system demonstrator is built and successfully tested.

OBJECTIVES: The horizontal distance between the back of the head and the frontal of the head restraint (backset) and rearward head movement relative to the torso (cervical retraction) were studied in different occupant postures and positions in a modern car. METHODS: A stratified randomized population of 154 test subjects was studied in a Volvo V70 year model 2003 car, in driver, front passenger, and rear passenger position. In each position, the subjects adopted (i) a self-selected posture, (ii) a sagging posture, and (iii) an erect posture. Cervical retraction, backset, and vertical distance from the top of the head restraint to the occipital protuberance in the back of the head of the test subject were measured. These data were analyzed using repeated measures ANOVA and linear regression analysis with a significance level set to p < 0.05. RESULTS: In the self-selected posture, the average backset was 61 mm for drivers, 29 mm for front passengers, and 103 mm for rear passengers (p < 0.001). Women had lower mean backset (40 mm) than men (81 mm), particularly in the self-selected driving position. Backset was larger and cervical retraction capacity lower in the sagging posture than in the self-selected posture for occupants in all three occupant positions. Rear passengers had the largest backset values. Backset values decreased with increased age. The average cervical retraction capacity in self-selected posture was 35 mm for drivers, 30 mm for front passengers, and 33 mm for rear passengers (p < 0.001). CONCLUSIONS: Future design of rear-end impact protection may take these study results into account when trying to reduce backset before impact. Our results might be used for future development and use of BioRID manikins and rear-end tests in consumer rating test programs such as Euro-NCAP.

Although whiplash injuries account for a significant annual cost to society, the exact mechanism of injury and affected tissues remain unknown. Previous investigations documented injuries to the cervical anterior longitudinal ligament in whiplash. The present investigation implemented a comprehensively validated computational model to quantify level-dependent distraction magnitudes of this structure in whiplash. Maximum ligament distractions approached failure levels, particularly in middle to lower cervical levels, and occurred during the initial phase of head-neck kinematics. In particular, the C5-C6 anterior longitudinal ligament sustained distraction magnitudes as high as 2.6mm during the retraction phase, corresponding to 56% of distraction necessary to result in ligament failure. Present results demonstrated that anterior structures in the lower cervical spine may be susceptible to injury through excess distraction during the retraction phase of whiplash, which likely occurs prior to head restraint contact. Susceptibility of these structures is likely due to non-physiologic loading placed on the cervical spinal column as the head translates posteriorly relative to the thorax. Injury to anterior spinal structures can result in clinical indications including cervical instability in extension, axial rotation, and lateral bending modes. Mitigation of whiplash injury may be achieved by minimizing head retraction during initial stages of 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.

The risk of whiplash injuries is affected by a complex interaction of the vehicle, seat, and occupant during an automobile collision. This article explores the vehicle, seat, occupant, and tissue responses to an automobile collision. Vehicles, and particularly bumpers, determine the properties of the collision pulse and seats transfer that pulse to the occupants. Occupants then interact with the seat back and head restraint, setting up multi-axial loads in the tissues of the cervical spine. The author reviews the pertinent literature, which demonstrates that the large variability in both occupant response and individual tissue injury tolerance levels may mean that vehicle and seat design improvements will not prevent whiplash injury in all individuals. The author notes that awareness of an impending impact may also reduce the potential for injury, however, pre-impact warning has not yet been considered for occupant protection.

A protocol has been proposed for testing seats for whiplash protection, however injury criteria have not yet been chosen. Assuming that whiplash symptoms arise from non-physiological motions of vertebral segments, we determined the ability of proposed criteria to predict peak individual vertebral displacements. Twenty-eight volunteers were subjected to rear impacts while seated in a car seat with head restraint, mounted onto a sled. Accelerometers were used to record head and torso accelerations. The volunteer data was used as a basis for testing post-mortem human specimens (PMHS). The seat was replaced by a platform onto which was mounted each of 11 cervico-thoracic spines. An instrumented headform was mounted to the upper end of the spine. The head restraint, head-to-restraint geometry, sled, and impact pulse remained the same. Head and T1 accelerations were measured and individual vertebral sagittal (XZ) plane rotations and translations were obtained from high speed video. Proposed injury criteria (NIC, Nkm, Nte, Nd) were tested for their ability to predict average, total, and peak intervertebral displacements. PMHS specimens had chest and head X (horizontal) and Z (vertical) linear accelerations similar to volunteers whose heads hit the head restraint. The best predictors were: Nd shear and peak intervertebral posterior translation (r(2) = 0.80), Nd extension and peak extension angle (r(2) = 0.70), and Nd distraction and peak distraction (r(2) = 0.51). Therefore consideration should be given to a displacement based injury criteria such as Nd in assessment of whiplash protection devices.

Rear impact sled tests were conducted using 5th, 50th, and 95th percentile Hybrid III dummies to evaluate proposed injury criteria. Different head restraint height (750, 800 mm) and backset (0, 50, 100 mm) positions were used to determine axial and shear forces, bending moments, and injury criteria (NIC, N(ij), and N(km)). The time sequence to attain each parameter was also determined. Three events were identified in the response. Event I was coincident with the maximum rearward motion of the torso, Event II occurred at the time of the peak upper neck flexion moment, and Event III occurred at the time of maximum rearward motion of the head. Parameters such as backset, head restraint height, seat-head restraint interaction, and anthropometry affected impact responses. Head rotations increased with increasing backset and increasing head restraint height. However, N(ij) and N(km) did not exhibit such clear trends. The 50th percentile dummy responded with consistent injury criteria values (e.g., the magnitude of the injury criteria increased with backset increase or head restraint height decrease). However, the 5th and 95th percentile dummies did not demonstrate such trends. These findings underscore the need to include subject anthropometry in addition to seat and head restraint characteristics for better assessment of rear impact responses.

Whiplash has increased over the past two decades. This study compares occupant dynamics with three different seat types (two yielding and one stiff) in rear crashes. Responses up to head restraint contact are used to describe possible reasons for the increase in whiplash as seat stiffness increased in the 1980s and 1990s. Three exemplar seats were defined by seat stiffness (k) and frame rotation stiffness (j) under occupant load. The stiff seat had k=40 kN/m and j=1.8 degrees /kN representing a foreign benchmark. One yielding seat had k=20 kN/m and j=1.4 degrees /kN simulating a high-retention seat. The other had k=20 kN/m and j=3.4 degrees /kN simulating a typical yielding seat of the 1980s and 1990s. Constant vehicle acceleration for 100 ms gave delta-V of 6, 10, 16, 24, and 35 km/h. The one-dimensional model included a torso mass loading the seatback, head motion through a flexible neck, and head restraint drop and rearward displacement with seatback rotation. Neck displacement was greatest with the stiff seat due to higher loads on the torso. It peaked at 10 km/h rear delta-V and was lower in higher-severity crashes. It averaged 32% more than neck displacements with the 1980s yielding seat. The high-retention seat had 67% lower neck displacements than the stiff seat because of yielding into the seatback, earlier head restraint contact and less seatback rotation, which involved 16 mm drop in head restraint height due to seatback rotation in the 16 km/h rear delta-V. This was significantly lower than 47 mm with the foreign benchmark and 73 mm with the 1980s yielding seat. Early in the crash, neck responses are proportional to ky/mT, seat stiffness times vehicle displacement divided by torso mass, so neck responses increase with seat stiffness. The trend toward stiffer seats increased neck responses over the yielding seats of the 1980s and 1990s, which offers one explanation for the increase in whiplash over the past two decades. This is a result of not enough seat suspension compliance as stronger seat frames were introduced. As seat stiffness has increased, so have neck displacements and the Neck Injury Criterion (NIC). High-retention seats reduce neck biomechanical responses by allowing the occupant to displace into the seatback at relatively low torso loads until head restraint contact and then transferring crash energy. High-retention seats resolve the historic debate between stiff (rigid) and yielding seats by providing both a strong frame (low j) for occupant retention and yielding suspension (low k) to reduce whiplash.

The objective of this paper is to present modeling and simulation of the effect of head restraint position on head/neck dynamics in rear-end motor vehicle collisions. Although individual injury tolerance levels vary, it is believed that properly positioned head restraints can be beneficial in reducing injury. The paper discusses the effects of restraint positioning by simulating a series of rear-end collisions using a finite-segment (lumped-mass) model of the human frame. It is found that proximity of the restraint to the head is the principal factor in preventing harmful whiplash motion. The findings suggest that "smart" head restraints could therefore significantly reduce whiplash induced injuries.

To assess the protective performance of seats and head restraints, occupant models able to mimic the motion of a human in a crash are needed. Hence, a new mechanical dummy neck for low-velocity rear collision tests was developed. The dummy neck consists of seven cervical elements connected by pin joints. The stiffness properties of the neck were represented by rubber blocks mounted between each pair of vertebrae, as well as by muscle substitutes between the head and the first thoracic vertebra (T1). The muscle substitutes consist of cables connected to a unit containing springs and a damper. The neck was validated against volunteer test data ( j v of 7 km/h) and compared with the kinematics of the Hybrid III dummy. The new neck was tested as a part of a new dummy (BioRID) that produced a human-like motion of the T1. The kinematics of the new neck was within the corridor of the volunteers, during the major part of the first 250 ms of the crash event, for both displacement of the head relative to T1 and for...

STUDY DESIGN: This study used rigid-body and finite-element models of forces in the cervical spine resulting from a rear-end motor vehicle impact based on data from 26 volunteer experiments. OBJECTIVES: To define the magnitudes and directions of internal forces acting on the cervical spine during rear-end impact, and to determine the effects of increasing the impact acceleration and the initial position of the occupant's head with respect to the head restraint. SUMMARY OF BACKGROUND DATA: In a number of studies using volunteers or cadavers, the kinematics of the occupant during a rear-end impact related to "whiplash" of the cervical spine have been reported. Few studies have described the mechanism by which internal spine forces are produced and how they may be affected by interaction of the occupant with the seat and head restraint during impact. METHODS: From a companion study on the response of 26 volunteers to rear-end impact, experimental data on head and torso accelerations were developed. Rigid-body mathematical dynamic modeling of a 50th-percentile male was implemented, along with a finite-element seat model, lap belt, and shoulder belt. The model was first subjected to a rear-impact pulse similar to that used in the volunteer study, first with a peak of 3.5 G, then with a peak up to 12 G. Initial head-to-head restraint distance in the model was varied from 1 to 12.5 cm. RESULTS: The major cervical spine forces were upper and lower neck shear causing intervertebral relative anterior displacements. Increasing the peak acceleration magnitude caused increased neck shear force magnitudes. With the head initially positioned closer to the head restraint, the time difference between the occurrences of the peak upper and lower neck shear forces was smaller; the C7-T1 intervertebral shear displacements were reduced; the head moved more in phase with the torso; extension of the head and neck was reduced; and late head flexion was increased. CONCLUSIONS: In this simulation, anterior shear was the major internal force acting in the cervical spine during rear-end impact. Increasing impact acceleration magnitude directly increased shear force. When the head was initially closer to the head restraint, the magnitude of the shear force was unaffected, but the time difference between its occurrences in the upper and lower neck was decreased and intervertebral translations were reduced. These results suggest how the seat could be improved to reduce peals forces and the time differences between them. Language: en

BACKGROUND: Whiplash injury claims have increased for two decades and manual head restraints are often incorrectly adjusted. A Self-Aligning Head Restraint (SAHR) was designed to move upward and forward by occupant motion in a rear crash providing earlier neck support, even when the head restraint is positioned low. This study determines its field effectiveness. METHODS: Insurance records were analyzed for consecutive Saab rear crashes in Sweden over 18 months. The Saab 9000/900 had standard head restraints and Saab 9-5/9-3 had SAHR. A questionnaire was mailed to the occupants, insurance and medical records were reviewed, and phone interviews were conducted. RESULTS: SAHR reduced whiplash injury risks by 75 +/- 11% from an 18 +/- 5% incidence in 85 occupants with standard head restraints to 4 +/- 3% in 92 occupants with SAHR. No SAHR seat required repair or replacement after the crashes. CONCLUSION: SAHR is effective in reducing whiplash injury in rear crashes and is a passive public-health approach that works irrespective of manual head-restraint adjustment.

Significant progress in car occupant safety has been made through the use of safety devices such as airbags and seat belts, as well as in the construction of the car body itself. Much still needs to be done, however, in order to satisfy increasingly stringent legislation and public demand. This work deals with the problem of whiplash injuries which so far, due to difficulties in diagnosis, have been very difficult to investigate let alone prevent. A new advanced biomechanical FE model of the head-neck complex has been created and combined with the Hybrid 111 FE dummy model, which is an industry standard for occupant safety. The final model has been used to study whiplash accidents for a representative range of car seats. The simulation clearly shows the effects of seat back stiffness and head restraint position. It also illustrates the unique contribution that is possible for combined biomechanical/dummy modelling in vehicle safety design, considering a simple whiplash protection device.

Neck injury resulting from rear impact (often known as whiplash) is a serious cause of road trauma. It is often underestimated or overlooked because such injuries are minor on traditional injury scales but can result in long term pain and disability. The paper begins with a brief review of research into head restraints and whiplash done so far. A review of international head restraint regulations revealed the absence of any horizontal offset requirements. A review of seat strength requirements and testing procedures showed that a regulation that required a collapsible seat would involve significant compliance testing. This paper concludes a preliminary project conducted by the Federal Office of Road Safety (FORS) where the head restraints for twenty Australian market vehicles were assessed using known performance criteria. A key finding of the report was that most of the vehicles allowed for vertical adjustment of the head restraint. Also important was that none of the vehicles measured allowed horizontal adjustment and on some of the head restraints the horizontal displacement increased as the vertical height increased. As the understanding of neck injury mechanisms in rear impact develops, there may be some scope for FORS to facilitate the improvement of these standards. Further research into neck injury mechanisms may reveal yielding seat backs or new 'active' head restraint technology as a more effective countermeasure. In the meantime, educating occupants to correctly adjust their head restraints seems to be an effective way to reduce injuries in existing vehicles.

This two-year investigation was designed to estimate the incidence of driver neck pain in rear-struck vehicles involved in two-vehicle collisions and to determine the relationship between neck pain and specific vehicle, human, and environmental factors. Neck pain percentages were significantly higher for female (45%) than for male (28%) drivers. For female and male drivers, neck pain likelihood increased as head restraint height decreased below the head's center of gravity, although this effect was significant only for females. Head restraint backset, the horizontal distance measured from the back of the driver's head to the front of the head restraint, was not found to be related to neck pain for female drivers. Backset trends for male drivers could not be evaluated because few male drivers had head restraints that were high enough for backset to be relevant. Reported neck pain decreased for older drivers (females only), drivers in less severe crashes, and drivers in heavier cars (females only); all head restraint analyses were adjusted for these characteristics. Women, and most likely men, in the United States would benefit greatly from international harmonization to European head restraint standards. Until then, both women and men should be encouraged to adjust their adjustable head restraints, if possible, behind their heads' centers of gravity and to sit with the backs of their heads as close as possible to their head restraints.

To analyze the effect of the seat characteristics on dummy motions and human volunteer motions, sled tests simulating low-speed rear impacts were conducted with some seats which had different characteristics. Volunteer's cervical vertebral motions were photographed with an X-ray cineradiographic system at a speed of 90 frames/s as well as the visible motions of dummy's and volunteer's were recorded. Although the tests were conducted under limited conditions, the results indicated the relationship between the occupant's visible motions, which are assumed to be closely related to the whiplash injury mechanism, and seat characteristics. It should be noted that the volunteer sled tests were discussed and approved by the Tsukuba University Ethics Committee and the volunteer submitted his informed consent in writing in line with the Helsinki Declaration.

Police based national accident data from the Netherlands show an enormous increase of both in number and in share of car rear-end collisions resulting in injury over the last 15 years. The average severity of those accidents remains low (illustrated by very low shares of occupants killed or hospitalised). However, the apparent increase in number of less severely injured as well as the personal and societal consequences of their injuries may well impose an increasing threat to the quality of life within the Dutch society. Based on national accident data as well as other relevant injury and traffic exposure data, the current situation in the Netherlands is described. Differences with respect to gender unexpectedly suggest that female drivers have a higher risk of their car being hit from behind than male drivers do. Less unexpectedly, differences are found between males and females with respect to injury susceptibility. These differences are analysed using controlling factors such as type of car, type of road, and exposure to traffic. It appears that not all of the indicators used point the same way; some of the increase mentioned may be due to registration biases. There is also a lack of adequate data with regard to the real number of whiplash injuries, their severity, and the longer-term consequences. Even if the total scope of the problem of whiplash injury in the Netherlands is still not fully known, the current estimate of societal consequences implicates a need for preventive measures. In the first place, accident prevention should be considered and a number of possible preventive measures (such as infrastructural improvement and application of ITS devices in cars to maintain distance in traffic) are discussed. Injury preventive measures (such as in car protection against whiplash) are already more generally available but still need much improvement.

An important detail referring to the whiplash syndrome is the relationship between the position of the head restraint and the head, because the head restraint protects the head in case of a rear-end accident. This relationship was evaluated in a representative study in 601 nonselected volunteers. A horizontal distance between the head and head restraint of maximal 9 cm was present in 69.6%. An optimal distance of 0 cm was only found in 7.4%. Just 50% of the adjustment distance was used by the car drivers. Even in completely distracted adjustments in 50% a deficit of more than 8 cm, and in 20.9% a deficit of even more than 12 cm was present. These results show that passive protection, on the one hand, is not guaranteed because of the lack of proper height adjustment. On the other, the volunteers did not use the best adjustment each time.

Neck injury by rear-end collision occurs frequently in automobile accidents, yet its pathomechanical process has not been investigated. For the purpose of developing a better seat and head restraint to reduce whiplash injuries in rear-end collisions, we performed impact analyses using finite element models of the human head and neck, and a new neck model in rear-end collisions. A pseudo 3D FEM model using a rear-end collision of 5.7 km/h was prepared. The FEM results showed a higher tensile stress localized in anterior longitudinal ligaments during impact. Compressire stresses localized in soft tissues, reached its maximum value at 140 ms after collision. We also compared the results displacements of head relative to chest with and without headrestraint and head angles on sled test of the new neck model, the dummy and volunteer. It is clear that the new neck model in rear-end collision behaves closer to that of human neck than the conventional dummy neck.

Whiplash is the most common injury type arising from motor vehicle collisions, often leading to long-term suffering and disability. Appropriately positioned geometrically suitable head restraints play a important role in protecting vehicle occupants from whiplash injury. Previous available literature suggests that many drivers do not correctly adjust their head restraints due to a lack of awareness of the consequences of incorrect adjustment. Surveys conducted on the general population demonstrated that they were unaware of how head restraints protect them and believed that their current head restraint adjustment was adequate. In general, there is a low awareness about the protective value of head restraint appropriate adjustment. Based on the available literature, there is a significant lack of public awareness surrounding the proper use and correct adjustment of head restraints. It is not only the general public who are unaware of correct positioning, but also those in the medical profession [7]. Health care practitioners are well poised to play a vital role in preventing whiplash injury by educating their patients about traffic safety value of appropriate head restraint adjustment.