Documentation:FIB book/Effect of Head Restraint Design and Regulation on Whiplash

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Overview

Introduction

Road traffic crashes are the most common cause of cervical spine injuries. Of the various types of cervical spine injuries, the least serious yet most common are musculoligamentous strains - also known as whiplash.[1] Due to the low severity nature of this injury, there are low reporting rates and low admittances to hospitals, resulting in no reliable estimates of whiplash per year.[1] However, annual counts of whiplash likely exceed 1.2 million in the US[1] and 28-53% of traffic collision victims suffer from this type of injury.[2]

Whiplash is a term applied to a group of injuries from the same mechanism of occurrence[3], which is the motion of the head and neck relative to the torso[4] experienced from a sudden acceleration-deceleration force on the cervical spine due to a collision.[5] It is usually a nonlife-threatening musculoligamentous injury[5] but is difficult to diagnose because of the delay in the onset of symptoms. Due to the late symptoms, whiplash injuries are often not immediately reported to police investigators and thus makes data collection difficult.[6] Common symptoms of whiplash include neck and back pain, vertigo, dysphagia, and headaches.[4] Long term health consequences such as chronic symptoms affect 30-50% of people who have experienced whiplash, leading to a reduced quality of life.[7] Additionally, there is a high economic burden of this injury of a reported $9 billion cost in the US annually.[7] In comparison, the US Department of Transportation has estimated in 2002 that car manufacturers spent $5.42 on front and rear head rests per car. [8]This comes out to about $85 million spend to reduce whiplash[8], which is much smaller than the financial strain caused by treating and managing these injuries.

A major preventative measure for whiplash are head restraints which, in the most ideal position, can decrease the amount of head and neck motion relative to the torso. We will investigate the effect of headrest design and position on whiplash rates with a focus on the mechanics of whiplash from rapid hyperflexion and hyperextension of the neck. This review will cover the history and background of head restraints, the biomechanics of whiplash, the type of traffic crashes that can cause whiplash, regulations of head restraints, and finally explore current and future work.

History

An early head rest design from a 1972 AMC (American Motors Corporation) Sedan

The term whiplash was first coined by Arthur G. Davis in “Injuries of the Cervical Spine” in 1945[9] but generally attributed to Gay and Abbot's “Common Whiplash Injuries of the Neck” in 1953.[10][3]

Head restraints, sometimes mistakenly called headrests, were first patented by Benjamin Katz in 1923.[5] Head restraints as a device to prevent whiplash was first proposed by Albert D. Ruedemann Jr in 1957.[4] Since then, head restraints have become mandatory for vehicles and are understood to be an important tool in preventing neck injuries in car crashes.[8]

Regulations for requiring head restraints were first seen in the GSA Standard 515/22, predecessor to the FMVSS 202, on October 1st, 1967 for vehicles purchased by the U.S. Government. Starting January 1, 1969 passenger cars are required by FMVSS No. 202 to have head restraints in the front outboard seating positions. September 1, 1991, FMVSS No. 202 extended to light trucks, multipurpose passenger vehicles, and buses with a gross vehicle weight rating of 10,000 pounds or less.[4]

Biomechanics of Whiplash

Whiplash is defined as an injury to one or more of the cervical spine that arises from inertial forces being applied to the head in the event of a motor vehicle accident. It has also been categorized as a soft tissue injury but the mechanism is not broadly understood. [11] Some studies have suggested cervical facet capsule ligament strains and capsular elongation are likely mechanisms of injuries.[11] [12] The capsule facet joints and ligaments innervating the lower cervical facets can exceed physiological limits during whiplash, potentially causing tensile failure. [12] Current studies support the explanation of capsule stretch/elongation and rupture as being a likely contributor to whiplash, but this is still generally under investigation. [12] [13]Other injury mechanisms suggested have been hyperextension of the neck, muscle strains, spinal column pressure pulses, facet impingement and more.[11][14]

An analysis of a high speed film revealed the bi-phasic kinematic response of the cervical spine. [14] During the first phase, the cervical spine assumes a S curvature. The upper level of vertebrae is flexed whilst the lower is in extension.[14] Shear and tensile axial forces act along the entire cervical spine at this point during the crash.

The second phase represents the entire cervical spine bending into extension.[14] The maximum intervertebral extension occurs in the lower level of the cervical spine during the first phase of whiplash. In this phase, axial compressive forces on the neck decrease whilst shear forces reach their peak as the neck rocks back into full extension. [14] This phase is exasperated when subjects are improperly positioning automobile head restraints.[14]

Shear Forces

During a rear impact event, horizontal forces perpendicular to the cervical spine induce shearing between the vertebrae.[14] This shearing causes compression in the facet joint surface, peaking during phase two of whiplash injury. Shear forces can cause stretching of the anterior intervertebral disc fibers resulting in inflammation and pain. Despite being a part of the biomechanics of whiplash injuries, shearing forces are the least commonly observed.[11] Yeung's 1996 paper, "rotational and shearing forces tend to produce more severe injuries such as dislocations and fractures". [15] These cervical spine dislocation can lead to disc herniation, ligament, muscle, and discs injury, and instability (abnormal range of motion or positioning of the cervical spine).[11]

The shear forces (blue) and compressive forces (red) are shown on some cervical spine vertebrae in s-curve shape to demonstrate what forces they are experiencing during whiplash.

Compressive Forces

During phase one, neck axial forces can cause compression of the cervical spine. Although these forces peak during the first phase of whiplash injury, they persist throughout.[16] Compression might cause the loosening of ligaments which makes it easier for facet joint capsule and intervertebral injuries caused during shear, to occur.[16]

Diagram of the cervical spine in hyperflexion and hyperextension of the cervical spine. Whiplash generally occurs during a rapid transition from hyperflexion to hyperextension of the cervical spine. This may cause various soft tissue injuries.

Extension

The lower region of the cervical spine undergoes forced extension during rear impact of motor vehicle accidents. This extension subjects posterior structures to compressive forces and anterior structures to tensile forces. [11] During extension, the facet joints are the first incident of contact first experiencing cartilage compression which is followed by further stretching the anterior structures, beyond the elastic limit resulting in the tearing of muscles and ligaments.[11] Furthermore, discs of the cervical spine can be damaged from being torn, separated, or fractured of the vertebral body.

Flexion

Hyperflexion of the neck occurs after the rebounding of the head from the headrest in the secondary phase of whiplash. This hyperflexion applies compressive forces to the anterior elements and tensile forces to the posterior elements of the cervical spine.[16][14] These swift and atypical motions generate forces, notably shear and compression forces, resulting in harm to the soft tissues surrounding the head and neck.

Methodology

In the realm of whiplash biomechanics research, two primary data collection methodologies observed in literature. The first approach involves physical experiments using cadaveric cervical spines, providing direct insights into the mechanical behavior under whiplash conditions. This method offers a biofidelic representation of anatomical and material properties. The second approach employs advanced computational models, specifically finite element models (FEM), to simulate and analyze the impact of whiplash on the cervical spine. This technique allows for controlled, repeatable investigations and the capability to simulate a wide range of collision scenarios, though the collection method is reliant on the model's accuracy and underlying assumptions of it's anthropometry. Both methodologies pose important and distinct approaches to quantifying injury biomechanics of whiplash trauma and the resulting musculoligamentous strains.

In the 1998 study conducted by Panjabi et al[14]., whiplash trauma was investigated through an innovative experimental approach. A sled, mounted on horizontal linear bearings, was accelerated by pneumatic pistons. To replicate the dynamics of a whiplash injury, a cadaveric cervical spine was strategically suspended from its center of gravity, with an additional weight emulating the head of a 50th percentile male. This apparatus was subjected to rear-end collision forces, thereby inducing a forward acceleration of the head, effectively simulating the 'whiplash' motion. The movement was captured at a high frame rate of 500 frames per second, facilitating detailed biomechanical analysis. Subsequently, the captured images were analyzed to assess intervertebral rotations, while head motion was quantitatively evaluated using data derived from three potentiometers. The range of accelerations used in this study was from 2.5 g to 10.5 g. [14]

Contrasting Panjabi et al.'s 1998 study, a more contemporary 2018 research by Huang et. al. [2] explored the impact of neck muscles on cervical spine injuries due to whiplash using a finite element model (FEM) tool. This study employed an advanced active head-neck FEM, representing the 50th percentile adult male, and validated it against experimental data in frontal, rear-end, and side impact conditions. The model was used to simulate the cervical spine's response to frontal collisions ranging from 8 g to 22 g and rear impact collisions from 4 g to 10 g. Injuries were quantified by analyzing the relative motion of cervical vertebrae and applying whiplash injury criteria such as NIC, Nkm, and Nij to evaluate various parameters. [2]

Comparing the two studies, each has its advantages and disadvantages in categorizing whiplash injury biomechanics. Panjabi et al.'s physical experiment with a cadaveric spine provided direct, biofidelic insights into the mechanical response of the cervical spine under whiplash conditions. This approach offers biofidelic anatomical and material properties (limited due to degrading tissues) but is limited by the variability in cadaveric specimens and approximation of head response to average weight values. On the other hand, Huang et al.'s 2018 FEM study done allowed for a more controlled, repeatable, and customizable investigation of whiplash injuries using computer modelling. The use of FEM enables the analysis of different scenarios and conditions that would be difficult or impossible to replicate physically with consistency across tests. However, its accuracy is contingent on the model's biofidelity and the validity of the assumptions made for tissues, muscle response, and material properties, potentially limiting its applicability to real-world scenarios. Both studies contribute significantly to the understanding of whiplash injury biomechanics, offering different perspectives and methodologies.

Quantifying Whiplash

Due to the large number of parameters that can affect and cause whiplash, being able to quantify the injury and investigate the sources of whiplash remains difficult. Neck injury criterions such as Nij, Nkm, and NIC have limitations as there may not always be a direct correlation between the severity of whiplash symptoms and the intended use of these criteria[17][18][19]. These criteria are developed from mathematical formulations based on the mechanism of injury and measurements of acceleration, force and intervertebral displacement.[20][13] However, the nature of whiplash injuries pose a difficult problem; The primary validation for these criteria is comparison with cadaveric studies, but these studies encounter difficulties when identifying minor soft tissue injuries. [13]

Nij and Nkm Criterion

Nij and Nkm are functions of the dynamic loads at the occipital condyles, which form the joint between the highest cervical vertebrae and the occipital bone. The bending moment is quantified by Nkm and Nij, shear force is quantified by Nkm, and axial forces are quantified by Nij.[13] The equations for Nij and Nkm are shown below:

[17]

[18]

Nij critera is normally used when subjects poses injuries with AIS 2 distinction or greater, whilst Nkm is normally used during AIS 1, both have an injury threshold value of 1.0.[20] In a 2010 study by Ivancic & Sha found that average peaks for Nij and Nkm in their tests were found to be way below the injury threshold criteria of 1.0[20]. However, given the intended use of Nij and Nkm to predict more serious injuries, these low values were expected.[20] In order to apply Nij to predict soft tissue whiplash injuries, studies suggest the threshold would need to be lowered.[20]

NIC Criterion

The NIC (Neck Injury Criterion) was developed for low-speed rear-end Impacts, based on the relative horizontal motion between head (C1) and chest (T1).[19] Calculated using the equation below:

[19]

The 1998 study by Wheeler et al. found that a neck injury criterion (NIC) could not predict whiplash symptom occurrences.[21] The NIC was proposed based on the relative acceleration and velocity between the top and bottom of the cervical spine and the threshold NIC value was proposed to be 15, for AIS-1 cervical injury.[21][20] The NIC validation tests were performed by using kinematic and clinical data of human subjects in rearward vehicle impact tests. However, none of the NIC values exceeded the proposed threshold of 15 , yet an overall 33 percent of the tests resulted in whiplash symptoms.[21] This implies that the suggested threshold is excessively elevated. This is due to the fact that, when contrasted with human subjects, the manifestation of whiplash symptoms occurred at values below the threshold for one-third of the participants in the study. Furthermore, predicting whiplash using NIC (or other load-based criteria) in test-dummies is limited because present dummies are not usually equipped with intervertebral motion measurement devices.[20] Without compliance with current test dummies, it is very difficult to implement NIC as a standard for determining the onset of whiplash.

The reasons discussed to justify why NIC could not predict whiplash occurrence was because there may not be a correlation between the severity and duration of whiplash symptoms and the intended use of NIC. There were found in the human subjects no significant differences in reflex, sensory, or upper extremity muscle strength, suggesting that the symptoms are not nerve based.[21] Additionally, NIC is typically used to predict neck injuries and for the evaluation of safety systems, but because NIC compares motion between thorax and head, data at the intervertebral level is left unaccounted for.[20] This may contribute to discrepancies between NIC predictions and whiplash symptom occurrence's because intervertebral is required. This is consistent with the current hypothesis which states that whiplash injury is related to intervertebral capsule elongations or strains. [11][12]


After reviewing different papers utilizing each criteria, no single criteria in the current iteration seems adequate for encapsulating the entire range of whiplash injuries. This should be taken into account when analyzing regulations or testing relying on evaluation using one sole evaluation criteria listed here. Combinations of these criteria, or other quantifiable tests are much more robust tests for understanding the onset of whiplash injury.

Regulations

FMVSS No. 202

Initial Regulations - 1969

Head restraints were first made widely known in 1969 to prevent neck hyperextension and mitigate whiplash injuries. The initial standard required either of 2 conditions to be followed:

  1. The rearward angular displacement of the head reference line to be less than 45 degrees from the torso reference line during a forward acceleration of 8g.[8]
  2. The head restraint must be at least 700 mm above the top of the seat in their highest position. The head restraint must not deflect more than 100 mm when under a 373 Nm moment and must withstand a rearward load of 890 N before failure.[8]

After the implementation of head restraints in 1969, NHSTA conducted a head restraint evaluation in 1982[22]. It was found that integral head restraints, meaning non-adjustable head restraints, were 17% effective in reducing rear impact injuries while adjustable head restraints were 10% effective[22]. The difference between effectiveness was assumed to be due to adjustable head restraints being positioned improperly, such as being positioned too low, so that neck hyperextension was not reduced to its full potential. The effectiveness for reducing whiplash injuries was found to be 28.3% and 16.7% for integral and adjustable head restraints respectively[22]. This shows that head restraints are only effective in reducing whiplash injuries, not preventing them.

Final Rule

In 2004, NHSTA officially published The Final Rule which upgraded the FMVSS No. 202 to require higher head restraints that are closer to the head and available in front outboard positions.[8] Front outboard positions include the driver's seat and the outside front passenger seat, excluding passenger seats separated from the passenger door with passageways to access the cargo area.[8] The upgrades for the front outboard sets required adjustable head restraints to have the lowest and highest possible position of 750 mm and 800 mm respectively, measured from the seating reference point.[8] Adjustable head restraints must lock in a vertical position under a downward force.[8]

The backset is measured as the distance between the back of the head and the head restraint. Based on computer modelling performed by NHSTA using a 50th Hybrid III dummy[8], it was found that the backset has an influence on the amount of force felt by the neck and has a correlation to the length of time that a person is disabled by injury. The new requirement limited the amount of backset to 55 mm or less at any height adjustment position.[8] If the backset is adjustable to less than 55 mm, the head restraint must lock under the application of a rearward load.[8]

It was decided that if the rear seat back structure has a height of at least 700 mm in any position of adjustment, it would be considered a rear head restraint.[8] This definition allows regulation for most rear adjustable and adjustable head restraints in the market.[8] However FMVSS 202a does not require rear head rests to be included in any vehicle.[23] Though the consistent use of rear head rests potentially indicates consumer demand is what's pushing manufacturers to include them rather than regulations. However, any rear head rests included must demonstrate through testing to withstand forces that are determined to prevent whiplash by FMVSS 202a.[23]

Testing

The FMVSS imposes several restrictions on head rests in an effort to reduce whiplash rates. As mentioned in the regulation section, the creation of the first tests emerged in 1967 and 1969 and mainly focus on backset and height maximums.[24] In the current FMVSS 202a, there are 11 different results car manufacturers have to meet including heights, widths, gaps, backsets and strength.

Height Limits

One of the main focuses of testing is the height minimums and maximums.

In FMVSS 202, the first limit proposed was 711 mm for the driver headrest was determined after testing crashes at 48 km/h.[25] All manufacturers only used a 95th% male ATD. At the time, this was the only height requirement manufacturers had to meet.[25] Additional tests in 1969 reduced this height to a 700 mm minimum or an angle of 45 degrees or less between the head and torso.[25] Both these tests focused on head height since that was thought to be the main determiner of whiplash injuries.[25]

Test Example of FMVSS 202aS Energy Absorption Test with Linear Impactor[24]

Energy Absorption/Dynamics Test

Since the release of the Final Rule, car manufacturers have to demonstrate their head restrains can withstand the forces from a head during collisions is a major standard in FMVSS 202a.

Test Setup for FMVSS 202aS Energy Absorption Test with Linear Impactor[24]

In the energy absorption test, a linear actuator is slammed into the head rest. The impactor is 6.78kg and is accelerated up to 80g and travels at 24.1 km/h before colliding with the head rest. [24] It passes the test if it has at least "785 m/s2 maximum deceleration for more than 3 milliseconds".[24] The test setup details are outlined on three pages in the FMVSS 202aS which cover the laboratory test procedures for FMVSS 202a.[24] The documents outlines many details including distances and acceptable temperature ranges in an effort to maintain consistency between manufacturers.[24] The upper image in this section shows the impactor in an actual vehicle test. The black lines help mark measurement required by FMVSS 202aS and are used during post analysis to determine the acceraltions. The lower figure shows the test set-up more generally from FMVSS 202aS.

Another test currently proposed but not adopted is for the impactor requirement from FMVSS 202a to be replaced with the dynamic test alternative.[25] It is suggested as an option to push companies to continue head restraint development.[25] To pass these tests, a 95th% male ATD must be used in the driver’s seat and a 50th% male ATD in the passenger seat.[25] To provide contrast between the two ATDs, the head rests are positioned to two different heights.[25] Both must not exceed HIC 150 in a 15 ms window.[25] Furthermore, the driver ATD must not exceed 20 degrees and the passenger must not exceed 12 degrees.[25] The addition of the passenger ATD also gives a more comprehensive look at the impact of rear collisions on more occupants and that head rests can accommodate those with various heights. However this has not been integrated into FMVSS 202a yet.

Challenges and Future Work

Challenges

Head Restraints were introduced in the 1960s limiting relative motion of the head and thorax, however, this resulted in only a 13-18% reductions in neck injury claims.[26]

Addressing challenges in headrest design, testing, and research is crucial for mitigating the risks of neck injuries and fostering new innovations in the context of automotive collisions.[8] A major challenge and the most common reason for insufficient neck protection in rear impact collisions is the incorrect positioning or absence of proper headrest adjustment by vehicle occupants.[4] Individuals when entering into a vehicle are unlikely to adjust the headrest position compromising the features effectiveness in preventing whiplash.[26] Similarly, older fixed position headrests are not optimally placed to prevent whiplash and may in fact enhance hyperextension.[26]

Previous studies on whiplash primarily rely on geometric measurements of the head restraint, overlooking the dynamics of spinal kinematics during rear impact collisions.[14]This highlights a critical gap in the understanding of the factors contributing to neck injuries.[11] Another challenge lies in the evolving design of headrests and lack of testing standards for these innovations. There is currently no standardized procedure for testing and rating these new configurations, this lack of standardization limits the efficacy to ensure the safety of new systems.[4]

Limited research exists of the connection of the head restraint structures and trajectories which limits the ability to develop strategies to effectively reduce whiplash injuries.[27] To enhance safety standards, future research should address these limitations focusing on gaps in headrest design, usage, kinematics, and assessment methods.

Future Work

Automotive safety standards are increasingly focusing on innovations in active headrest positioning, the design of headrest connections, and the study of kinematic trajectories.[27] Notably, the introduction of active headrests marks a shift from traditional passive designs. For instance, BMW has developed a headrest that extends forward as the passenger leans forward, using load sensing technology.[25] This active design responds dynamically to collisions, minimizing the gap between the occupant's head and the headrest.[25] These headrests incorporate sensors and mechanisms to facilitate movement along specific trajectory paths.[27][25]

Additionally, research into the trajectories of seats, headrests, and occupants' heads has lead to divergence from conventional rigid two-pin headrest connection in most vehicles. The innovative design replaces the traditional pin connection with a guide slot, allowing the headrest to move upward and forward during a collision.[27] This movement restricts the head's translation and rotation, enhancing the headrest's effectiveness.[27] The goal is to align the headrest movement with predicted trajectory paths, providing more targeted support during an impact.[27]

The current literature on automotive safety, particularly regarding the development of active headrests and headrest connection designs, offers a promising outlook but also presents certain limitations.[27][6][25] A key strength is the focus on dynamic response systems, like BMW's load-sensing headrest, which demonstrate a significant advancement over passive systems.[6][25] This proactive approach in safety design could greatly reduce whiplash injuries.[25][6] The integration of sensors and mechanisms for trajectory control in headrests is another area where the literature shows considerable innovation, reflecting a deep understanding of biomechanical responses in collisions.[27]

However, the literature also has weaknesses that need addressing in future research. One major limitation is the lack of extensive real-world testing data, which is crucial to validate the effectiveness of these new systems under diverse and unpredictable collision scenarios.[25] Additionally, there is a gap in the consideration of different occupant physiologies[14]. Most designs and studies are based on average measurements, which may not be representative of the entire population. This can lead to safety features that are not optimized for all users, potentially reducing their overall effectiveness. Lastly, there is a need for more comprehensive cost-benefit analyses in the literature. While the advanced technology in active headrests promises improved safety, it also likely comes with increased production costs,[8] which could impact market accessibility and consumer adoption. Future research should aim to address these gaps, ensuring that advancements in automotive safety are both effective and inclusive.

References

  1. ↑ 1.0 1.1 1.2 Freeman, M., & Leith, W. M. (2020). Estimating the number of traffic crash-related cervical spine injuries in the United States; An analysis and comparison of national crash and hospital data. Accident Analysis & Prevention, 142, 105571. https://doi.org/10.1016/j.aap.2020.105571
  2. ↑ 2.0 2.1 2.2 Yan, Y., Huang, J., Li, F., & Hu, L. (2018). Investigation of the effect of neck muscle active force on whiplash injury of the cervical spine. Applied Bionics and Biomechanics, 2018, 1–10. https://doi.org/10.1155/2018/4542750
  3. ↑ 3.0 3.1 Dowling, J. J. (1964). “Whiplash” injuries. American Association of Industrial Nurses Journal, 12(5), 12–35. https://doi.org/10.1177/216507996401200503
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 NHSTA (November 1996). "Head Restraints - Identification of Issues Relevant to Regulation, Design, and Effectiveness".
  5. ↑ 5.0 5.1 5.2 Açar, B. (2021). Passive prevention systems in automobile safety. In Elsevier eBooks (pp. 406–414). https://doi.org/10.1016/b978-0-08-102671-7.10111-3
  6. ↑ 6.0 6.1 6.2 6.3 States, J. D., Balcerak, J. C., Williams, J. S., Morris, A. T., Babcock, W. R., Polvino, R., Riger, P., & Dawley, R. E. (1972). Injury frequency and head restraint effectiveness in Rear-End Impact Accidents. SAE Technical Paper Series. https://doi.org/10.4271/720967
  7. ↑ 7.0 7.1 Pink, J., Petrou, S., Williamson, E., Williams, M. A., & Lamb, S. E. (2016). Economic and Health-Related Quality of Life Outcomes of whiplash associated Disorders. Spine, 41(17), 1378–1386. https://doi.org/10.1097/brs.0000000000001512
  8. ↑ 8.00 8.01 8.02 8.03 8.04 8.05 8.06 8.07 8.08 8.09 8.10 8.11 8.12 8.13 8.14 8.15 "FMVSS NO. 202 Head Restraints For Passenger Vehicles" (PDF). Final Regulatory Impact Analysis. November 2004. |first= missing |last= (help)
  9. ↑ Davis, Arthur G. (January 1945). [doi:10.1001/jama.1945.02860030021006 "Injuries of the Cervical Spine"] Check |url= value (help). JAMA.
  10. ↑ Abbott, K. H. (1953). COMMON WHIPLASH INJURIES OF THE NECK. JAMA, 152(18), 1698. https://doi.org/10.1001/jama.1953.03690180020006
  11. ↑ 11.0 11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8 Barnsley, L., Lord, S., & Bogduk, N. (1994). Whiplash injury. Pain, 58(3), 283-307. https://doi.org/10.1016/0304-3959(94)90123-6
  12. ↑ 12.0 12.1 12.2 12.3 P. Quinn, Kyle (8 October 2006). "Cervical facet capsular ligament yield defines the threshold for injury and persistent joint-mediated neck pain". Journal of Biomechanics. 40: 2299–2306.
  13. ↑ 13.0 13.1 13.2 13.3 Smotrova, Ekaterina; Morris, Lucy; McNally, Donal (11 May 2021). "Comparison of standard automotive industry injury predictors and actual injury sustained during significant whiplash events". Eur Spine. 30: 3043–3058.
  14. ↑ 14.00 14.01 14.02 14.03 14.04 14.05 14.06 14.07 14.08 14.09 14.10 14.11 Panjabi, M. M., Cholewicki, J., Nibu, K., Grauer, J. N., Babat, L. B., & Dvorak, J. (1998). Mechanism of whiplash injury. Clinical Biomechanics, 13(4–5), 239-249. https://doi.org/10.1016/S0268-0033(98)00033-3
  15. ↑ Yeung, Ella (December 2023). "'Whiplash Injuries' of the Cervical Spine. The relationship between the Mechanism of Injury and Neutral Tissue Involvement" (PDF). Physiotherapy. 82: 5 – via Science Direct.
  16. ↑ 16.0 16.1 16.2 Chen, H. B., Yang, K. H., & Wang, Z. G. (2009). Biomechanics of whiplash injury. PubMed, 12(5), 305–314. https://pubmed.ncbi.nlm.nih.gov/19788851
  17. ↑ 17.0 17.1 Eppinger, Rolf; Kleinberger, Michael; Shashi, Kuppa; Roger, Saul; Sun, Emily (Jan 1 1998). "Development of improved injury criteria for the assessment of advanced automotive restraint systems" (PDF). United States. Department of Transportation. National Highway Traffic Safety Administration. Check date values in: |date= (help)
  18. ↑ 18.0 18.1 Schmitt, Kai-Uwe; Muser, Markus H.; Walz, Felix H.; Niederer, Peter F. (15 Sep 2010). "N km --A Proposal for a Neck Protection Criterion for Low-Speed Rear-End Impacts". Traffic Injury Prevention. 3:2: 117–126.
  19. ↑ 19.0 19.1 19.2 Boström, Ola; Svensson, Mats; Aldman, Bertil; Arne Hansson, Hans; Håland, Yngve; Lövsund, Per; Seeman, Torsten; Säljö, Annette; Örtengren, Tore (1996). "A NEW NECK INJURY CRITERION CANDIDATE-BASED ON INJURY FINDINGS IN THE CERVICAL SPINAL GANGLIA AFTER EXPERIMENTAL NECK EXTENSION TRAUMA" (PDF). Institute for Road Safety Research, SWOV: 123–36.
  20. ↑ 20.0 20.1 20.2 20.3 20.4 20.5 20.6 20.7 Ivancic, P. C., & Sha, D. (2010). Comparison of the whiplash injury criteria. Accident Analysis & Prevention, 42(1), 56–63. https://doi.org/10.1016/j.aap.2009.07.001
  21. ↑ 21.0 21.1 21.2 21.3 Wheeler, J. B., Smith, T., Siegmund, G. P., Brault, J. R., & King, D. J. (1998). Validation of the neck injury criterion (NIC) using kinematic and clinical results from human subjects in rear-end collisions. Proceedings of the International Research Council on the Biomechanics of Injury Conference, 26, 335–348. https://trid.trb.org/view/685094
  22. ↑ 22.0 22.1 22.2 Kahane, C. J. (1982). AN EVALUATION OF HEAD RESTRAINTS. FEDERAL MOTOR VEHICLE SAFETY STANDARD 202. NHTSA Technical Report. https://trid.trb.org/view/176976
  23. ↑ 23.0 23.1 "Federal Motor Vehicle Safety Standards; Head Restraints" (PDF). Federal Registry. National Highway Traffic Safety Administration (NHTSA), DOT. 11/02/2010. Retrieved 12/03/2023. Check date values in: |access-date=, |date= (help)
  24. ↑ 24.0 24.1 24.2 24.3 24.4 24.5 24.6 "LABORATORY TEST PROCEDURE FOR FMVSS 202aS Head Restraints - Dimensional and Static Testing" (PDF). U.S. DEPARTMENT OF TRANSPORTATION NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION. January 11, 2011. line feed character in |journal= at position 34 (help)
  25. ↑ 25.00 25.01 25.02 25.03 25.04 25.05 25.06 25.07 25.08 25.09 25.10 25.11 25.12 25.13 25.14 25.15 25.16 "Federal Motor Vehicle Safety Standards; Head Restraints" (PDF). National Highway Traffic Safety Administration. October 2nd, 2007. Check date values in: |date= (help) Cite error: Invalid <ref> tag; name ":23" defined multiple times with different content
  26. ↑ 26.0 26.1 26.2 Stemper, B. D., Yoganandan, N., & Pintar, F. A. (2006). Effect of head restraint backset on head–neck kinematics in whiplash. Accident Analysis & Prevention, 38(2), 317-323. https://doi.org/10.1016/j.aap.2005.10.005
  27. ↑ 27.0 27.1 27.2 27.3 27.4 27.5 27.6 27.7 Yang, Y., Kim, Y. & Jeon, E. Design for Headrest Including Guides Slot to Reduce the Neck Force in Rear End Impact. Int.J Automot. Technol. 19, 1041–1048 (2018). https://doi.org/10.1007/s12239-018-0101-5


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