Neck Injury Criteria Research Articles

Evaluation of the intervertebral neck injury criterion using simulated rear impacts

The Intervertebral Neck Injury Criterion (IV-NIC) is based on the hypothesis that intervertebral motion beyond the physiological limit may injure spinal soft tissues during whiplash, while the Neck Injury Criterion (NIC) hypothesizes that sudden changes in spinal fluid pressure may cause neural injury. Goals of the present study, using a biofidelic whole cervical spine model with muscle force replication, were to correlate IV-NIC with soft-tissue injury, determine the IV-NIC injury threshold, and compare IV-NIC and NIC. Using a bench-top apparatus, rear-impacts were simulated at 3.5, 5, 6.5, and 8 g horizontal accelerations of the T1 vertebra. Pre- and post-whiplash flexibility tests measured the soft tissue injury threshold, i.e. significant increases in the intervertebral neutral zone (NZ) or range of motion (ROM) above corresponding baseline values. Extension IV-NIC peaks correlated well with NZ and ROM increases at C0–C1 and at C3–C4 through C7–T1 ( r=0.64 and 0.62 respectively, p<0.001). Average IV-NIC injury thresholds (95% confidence limits) varied among the intervertebral levels and ranged between 1.5 (1.1, 1.9) at C5–C6 and 3.4 (2.4, 4.4) at C7–T1. The NIC injury threshold was 8.7 (7.7, 9.7) m 2/s 2, substantially less than the proposed threshold of 15 m 2/s 2. Results support the use of IV-NIC for determining the cervical spine injury threshold and injury severity. Advantages of IV-NIC include the ability to predict the intervertebral level, mode, severity, and time of the cervical spine soft-tissue injury.

An investigation into the head and neck injury potential of three-year-old children in forward and rearward facing child safety seats

This research focuses on the injury potential of children in forward and rearward facing child restraint seats in frontal collisions. Experimental sled tests were completed following the guidelines outlined in the Federal Motor Vehicle Safety Standard 213 using a Hybrid III 3-year-old dummy in a convertible forward/rearward facing child restraint seat. The seat was equipped with a five point child safety belt and the experimental test was completed in the forward facing configuration. The Hybrid III 3-year-old dummy was equipped with three uniaxial accelerometers arranged in mutually perpendicular directions in the head and chest. A numerical model employing a subset of the apparatus used in the forward facing experimental sled test was developed and numerically simulated using LSDYNA. To verify the numerical simulations, the head and chest accelerations were compared to the experimental findings and it was observed that a reasonable correlation between the data existed. Further numerical simulations were completed to investigate the influence of positioning the 3-year-old dummy in the rearward configuration on the head and neck injury potential during frontal crash. Through an analysis of injury criteria, using neck loads and head accelerations, it was observed that the rearward facing child dummy sustained significantly lower levels of neck injury criteria while exhibiting similar levels of the head injury criteria as the forward facing child dummy.

Development of a damping seat slide to reduce whiplash injury

To prevent whiplash injury, a new seat slide was developed. In the case of a rear-end impact, the device allows the vehicle seat to slide backwards while damping this motion. Deformable steel profiles serve as damping elements. To activate the device, a trigger system is used which detects an acceleration threshold. Sled test experiments were performed to analyse the behaviour of the new system. The tests were conducted to mimic rear-end collisions with a delta-V of 16 km/h. A BioRID dummy was used as a human surrogate. The results indicate the beneficial influence of the damping seat slide on the occupant kinematics. In particular, the so-called S-shape deformation of the neck assessed by the neck injury criterion (NIC) is reduced. Comparing a standard car seat with and without the damping seat slide, it was shown that the NIC is reduced by approximately 40 per cent. Hence it was shown that besides the head restraint and the recliner that are used in other whiplash protection systems, the seat slide has the potential to prevent whiplash injury.

Seat Properties Affecting Neck Responses in Rear Crashes: A Reason Why Whiplash Has Increased

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°/kN representing a foreign benchmark. One yielding seat had k = 20 kN/m and j = 1.4°/kN simulating a high-retention seat. The other had k = 20 kN/m and j = 3.4°/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 / m T , 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 influence of seatback characteristics on cervical injury risk in severe rear impacts

The determination of the optimum seatback characteristics for the mitigation of serious and catastrophic neck injury during high-speed rear-end collisions remains a topic of continued investigation. Despite a number of prior research efforts, both field data and sled test studies have yet to define a single optimal seatback performance criterion. Further, recent developments in seatbacks have introduced new designs into the field that have not been compared to more traditional designs. Analysis of NASS data from 1980 to 1999 demonstrated that at changes in velocity (Δ V) above 40 kph, rear-end collisions have a dramatically lower risk for catastrophic injury than frontal, near-side or far-side impacts. Unfortunately, owing to the small penetration of newer seatback designs in the automotive fleet, it is not possible to examine the influence of seatback design parameters on serious neck injury using these data alone. Accordingly, seven rear impact HYGE sled tests were conducted using a wide range of seat designs. Upper and lower neck load cells were used to measure neck forces and moments in restrained 50th male Hybrid III anthropomorphic test devices (ATD). Additionally, the neck injury criteria (Nij) was computed. Unlike prior studies that have examined the standard seated ATD or the dramatically out-of-position ATD, these tests were conducted using an ATD seated in non-standard but typical driving position. The results of this study indicate that several descriptions of seatback behavior, such as quasi-static ultimate force are poor predictors of ATD neck loading. It also suggests that, for the severe crash studied, an optimum range of seatback stiffness exists, which appears to be in the mid-range of seatback stiffnesses available in current production vehicles. These data continue to illustrate the complex relationship of seatback design parameters to neck injury risk.

Studies of neck injury criteria based on existing biomechanical test data

The mechanisms of injury of the human neck are potentially related to the forces and bending moments acting on the spinal column. An injury criterion that combines the effects of the time history of force and moment, N ij , has been adopted by the USA federal government for vehicle crash regulations. This paper presents two analytical approaches to evaluate the N ij injury criterion using previously published biomechanical data: a direct fit optimization analysis and a statistical analysis. The results show that no values used in the N ij criterion corresponding to compressive force, extension moment and flexion moment will optimally separate the injury and non-injury cases in the biomechanical data set. Only the tensile force allows identification of the injury risk. All indications are that increasing the weight given to moment decreases the accuracy of the prediction.

Benefits from a Retrofit Neck Protection System

AbstractBenchmark testing of existing seat designs reveals poor performance in low-speed rear impacts. The neck injury criterion (NIC) exceeds the limiting value of 15 for almost all seats without a whiplash protection system. As only few new car models offer this, a system for retrofit installation was developed and tested. The Retrofit Anti Whiplash System, AWS, consists of a yielding device which is fitted to the seat rails and allows the whole seat to rotate and move backwards. This reduces thorax acceleration and thus the NIC value. As the force required to actuate the device depends on the position of the seat, the system offers optimum protection for large and small occupants.Tests with the rear impact dummy BioRID show a noticeable reduction in NIC compared to the standard seat. Loadings to the neck at a rear impact speed change of a Delta v of 15 km/h (9.3 mph) with AWS are in the same magnitude as at 9 km/h (5.6 mph) without AWS. MADYMO simulations with real crash pulses have been performed, and...

Small female head and neck interaction with a deploying side airbag

Objective: This paper presents dummy and cadaver experiments designed to investigate the injury potential of an out-of-position small female head and neck from a deploying side airbag. Methods: Seat-mounted, thoracic-type, side airbags were selected for this study to represent those currently available on selected luxury automobiles. A computer simulation program was used to identify the worst case loading position for the small female head and neck. Once the initial position was identified, experiments were performed with the Hybrid III 5th percentile dummy and three small female cadavers, using three different inflators. Results: Peak head center of gravity (CG) accelerations for the dummy ranged from 71× g to 154× g, and were greater than cadaver values, which ranged from 68× g to 103× g. Peak neck tension as measured at the upper load cell of the dummy increased with inflator aggressivity from 992 to 1670 N. A conservative modification of the US National Highway Traffic Safety Administration’s (NHTSA’s) N ij proposed neck injury criteria, which combines neck tension and bending, was used. All values were well below the 1.0 injury threshold for the dummy and suggested a very low possibility of neck injury. In agreement with this prediction, no injuries were observed. Conclusions: Even in a worst case position, small females are at low risk of head or neck injuries under loading from these thoracic-type airbags; however, injury risk increases with increasing inflator aggressivity.

N km --A Proposal for a Neck Protection Criterion for Low-Speed Rear-End Impacts

Soft tissue neck injuries sustained in low speed rear-end collisions are of continued concern in road traffic. To assess the risk of sustaining such injuries, various neck injury criteria have been proposed. In this study a new candidate for such an injury predictor called N km was developed. It is based on a linear combination of shear forces acting in the sagittal direction and extension/flexion bending moments, both measured at the occipital condyles. Results from a total of 40 sled tests, all performed using the same test procedure, with various car front seat models, and using a Hybrid III/TRID as well as a BioRID dummy, were evaluated in order to validate the new criterion. Additionally, a mathematical model was set up to determine the behavior of the N km at a higher crash pulse than the one used in the sled tests. It was shown that the new criterion offers the additional possibility to assess the kinematic phase of forward motion. Furthermore, the influence of the seat design on its protective potential could be related to the N km values obtained and thus, the new criterion is eligible to be part of a standard seat test procedure.

The neck injury criterion: future considerations

The cost of whiplash injuries — both in dollars spent for medical care and disability, and in terms of human suffering — are quite high in westernized nations. This is of particular interest both from a public health perspective and a general societal one because the disorder is theoretically preventable: in the very least it can be minimized. This can be achieved with crash prevention strategies and improvements in vehicle safety design — especially with more effective seat back and head restraint systems. Toward the goal of developing a gold standard for safety research in this area, a neck injury criterion (NIC) was proposed by Boström et al. in 1996 (Boström O., Svennson, M.Y., Aldman, B. et al., 1996. In: Proceedings of the International Conference on the Biomechanics of Impact, Dublin, Ireland). This criterion considers the relative horizontal acceleration and velocity between the bottom (T1) and top (C1) of the cervical spine and has face validity based on current literature. However, the NIC has still not been subjected to rigorous scientific investigation or validation in terms of its representativeness of human occupant injury. Such investigation should specifically consider, first, whether the NIC provides an adequate proxy for all potential neck injuries due to whiplash and, secondly, whether the proposed threshold value of 15 m 2/s 2 is an appropriate level for the stated goal. Based on a review of recent literature, recent human volunteer crash tests by Wheeler et al. and the those of the Spine Research Institute of San Diego, and based on mathematical MADYMO analysis of the first real world crash pulse data, it appears that the threshold for acute injury in the general population is likely to require a lowering of the originally proposed NIC value, and additional parameters, such as considering a forward rebound phase or neck extension criteria may be necessary. The conclusions of this paper should be considered preliminary because the numbers of crash test subjects and real world injury victims does not allow for rigorous statistical analysis. Certainly, ongoing work will be necessary to investigate this further and larger scale analysis of more onboard crash data will prove invaluable.

Neck injuries in car collisions — a review covering a possible injury mechanism and the development of a new rear-impact dummy

A review of a few Swedish research projects on soft tissue neck injuries in car collisions is presented together with some new results. Efforts to determine neck injury mechanisms was based on a hypothesis stating that injuries to the nerve root region in the cervical spine are a result of transient pressure gradients in the spinal canal during rapid neck bending. In experimental neck trauma research on animals, pressure gradients were observed and indications of nerve cell membrane dysfunction were found in the cervical spinal ganglia. The experiments covered neck extension, flexion and lateral bending. A theoretical model in which fluid flow was predicted to cause the transient pressure gradients was developed and a neck injury criterion based on Navier-Stokes Equations was applied on the flow model. The theory behind the Neck Injury Criterion indicates that the neck injury occurs early on in the rearward motion of the head relative to the torso in a rear-end collision. Thus the relative horizontal acceleration and velocity between the head and the torso should be restricted during the early head-neck motion to avoid neck injury. A Bio-fidelic Rear Impact Dummy (BioRID) was developed in several steps and validated against volunteer test results. The new dummy was partly based on the Hybrid III dummy. It had a new articulated spine with curvature and range of motion resembling that of a human being. A new crash dummy and a neck injury criterion will be very important components in a future rear-impact crash test procedure.

Comparison of car seats in low speed rear-end impacts using the BioRID dummy and the new neck injury criterion (NIC)

Long-term whiplash associated disorders (WAD) 1-3 sustained in low velocity rear-end impacts is the most common disability injury in Sweden. Therefore, to determine neck injury mechanisms and develop methods to measure neck-injury related parameters are of importance for current crash-safety research. A new neck injury criterion (NIC) has previously been proposed and evaluated by means of dummy, human and mathematical rear-impact simulations. So far, the criterion appears to be sensitive to the major car and collision related risk factors for injuries with long-term consequences. To further evaluate the applicability of NIC, four seats were tested according to a recently proposed sled-test procedure. ‘Good’ as well as ‘bad’ seats were chosen on the basis of a recently presented disability risk ranking list. The dummy used in the current tests was the Biofidelic Rear Impact Dummy (BioRID). The results of this study showed that NIC max values were generally related to the real-world risk of long-term WAD 1-3. Furthermore, these results suggested that NIC max calculated from sled tests using the BioRID dummy can be used for evaluating the neck injury risk of different car seats.

Head restraints—the neglected countermeasure

In a rear-end crash, if an occupant’s head is unsupported it lags behind as the torso is accelerated forward. This causes the neck to change shape, first taking an s-shape and then bending backward in a ‘whiplash’ motion. This sudden differential movement of the head and torso can cause ‘whiplash’ injuries to the neck. This paper reviews methods to minimize the differential head/torso movement and reduce the resulting injuries, focusing on the necessary first step for prevention, which is a head restraint that is behind and close to the back of an occupant’s head during the crash. The history of head restraints since the 1950s is reviewed, with particular attention to advanced restraint designs that are proving effective in reducing whiplash injury risk in dynamic tests using a new crash test dummy neck and a new neck injury criterion.

Pressure measurements in the spinal canal of post-mortem human subjects during rear-end impact and correlation of results to the neck injury criterion

The aim of this study is to validate the pressure effect theory on human beings during a realistic rear-end impact and to correlate the neck injury criterion to pressure in the spinal canal. Sled experiments were performed using a test setup similar to real rear-end collisions. Test conditions were chosen based on accident statistics and recordings of real accidents. In particular, velocity change and acceleration level were reproduced similar to actual collisions. The head restraint as well as the seat back were adjusted to different positions. Two small pressure transducer were implemented to the spinal canal of postmortem human subjects and pressure measurement similar to the pig experiments (using exactly the same equipment) were performed. A total set of 21 experiments with four different subjects were performed. The subjects were additionally instrumented with triaxial accelerometers that allowed for calculation of the NIC criterion. Results showed that NIC and pressure amplitudes of the CSF correlate well and therefor NIC seems to be able to predict these amplitudes also for human beings. Conclusions whether these pressure effects induce soft tissue neck injuries or not could not be drawn and should be investigated in further research.

Dynamic response of the Hybrid III three year old dummy head and neck during side air bag loading

This paper presents the results from 14 tests designed to evaluate the response and injury potential of a Hybrid III three year old dummy subject to loading by a deploying seat mounted side air bag. An instrumented Hybrid III three year old dummy was used for tests in two different occupant positions chosen to maximize head and neck loading. Four seat mounted thoracic side air bags were used that varied only in the level of inflator output. The National Highway Traffic Safety Administration's neck injury criteria for complex loading were modified to include moment values for both anterioposterior and lateral directions. The results indicate that side air bags may be designed so that the forces and moments in the child dummy's neck are below injury threshold values during a side air bag deployment. While there is considerable uncertainty as to the validity of published injury criteria owing to the lack of child biomechanical data, this study demonstrates the sensitivity of child response to initial position which provides insight into placement and geometry of side airbag systems. Furthermore, the data indicate a relationship between airbag inflator properties and child dummy response for a given airbag geometry.

Dynamic responses of the head and cervical spine to axial impact loading

This study explores the inertial effects of the head and torso on cervical spine dynamics with the specific goal of determining whether the head mass can provide a constraining cervical spine end condition. The hypothesis was tested using a low friction impact surface and a pocketing foam impact surface. Impact orientation was also varied. Tests were conducted on whole unembalmed heads and cervical spines using a drop track system to produce impact velocities on the order of 3.2 ms −1. Data for the head impact forces and the reactions at T1 were recorded and the tests were also imaged at 1000 frames s −1. Injuries occurred 2–19 ms following head impact and prior to significant head motion. Average compressive load a failure was 1727 ± 387 N. Decoupling was observed between the head and T1. Cervical spine loading due to head rebound constituted up to 54 ± 16% of the total axial neck load for padded impacts and up to 38 ± 30% of the total axial neck load for rigid impacts. Dynamic buckling was also observed; including first-order modes and transient higher-order modes which shifted the structure from a primarily compressive mode of deformation to various bending modes. These experiments demonstrate that in the absence of head pocketing, the head mass can provide sufficient constraint to cause cervical spine injury. The results also show that cervical spinal injury dynamics are complex, and that a large sample size of experimentally produced injuries will be necessary to develop comprehensive neck injury models and criteria.