1: Traffic Inj Prev.  2003 Dec; 4(4): 315-23.  

Influence of seat foam and geometrical properties on BioRID P3 kinematic
response to rear impacts.

Szabo TJ, Voss DP, Welcher JB.

Biomechanical Research & Testing, LLC, Long Beach, California 90815, USA.
brtsd@aol.com

As the primary interface with the human body during rear impact, the automotive
seat holds great promise for mitigation of Whiplash Associated Disorders (WAD).
Recent research has chronicled the potential influence of both seat geometrical
and constitutive properties on occupant dynamics and injury potential.
Geometrical elements such as reduced head to head restraint, rearward offset,
and increased head restraint height have shown strong correlation with
reductions in occupant kinematics. The stiffness and energy absorption of both
the seating foam and the seat infrastructure are also influential on occupant
motion; however, the trends in injury mitigation are not as clear as for the
geometrical properties. It is of interest to determine whether, for a given seat
frame and infrastructure, the properties of the seating foam alone can be
tailored to mitigate WAD potential. Rear impact testing was conducted using
three model year 2000 automotive seats (Chevrolet Camaro, Chevrolet S-10 pickup,
and Pontiac Grand Prix), using the BioRID P3 anthropometric rear impact dummy.
Each seat was distinct in construction and geometry. Each seat back was tested
with various foams (i.e., standard, viscoelastic, low or high density). Seat
geometries and infrastructures were constant so that the influence of the
seating foams on occupant dynamics could be isolated. Three tests were conducted
on each foam combination for a given seat (total of 102 tests), with a nominal
impact severity of Delta V = 11 km/h (nominal duration of 100 msec). The seats
were compared across a host of occupant kinematic variables most likely to be
associated with WAD causation. No significant differences (p < 0.05) were found
between seat back foams for tests within any given seat. However, seat
comparisons yielded several significant differences (p < 0.05). The Camaro seat
was found to result in several significantly different occupant kinematic
variables when compared to the other seats. No significant differences were
found between the Grand Prix and S-10 seats. Seat geometrical characteristics
obtained from the Head Restraint Measuring Device (HRMD) showed good correlation
with several occupant variables. It appears that for these seats and foams the
head-to-head restraint horizontal and vertical distances are overwhelmingly more
influential on occupant kinematics and WAD potential than the local foam
properties within a given seat.

PMID: 14630580 [PubMed - in process]



2: Traffic Inj Prev.  2003 Sep; 4(3): 228-39.  

Seat influences on female neck responses in rear crashes: a reason why women
have higher whiplash rates.

Viano DC.

ProBiomechanics LLC, Bloomfield Hills, Michigan 48304-2952, USA.
dviano@comcast.net

Since the earliest crash investigations, whiplash has been found to occur more
often in women than men. This study addresses seat properties that may explain a
reason for the higher rates in women, and changes in whiplash in general over
the past two decades. Three exemplar seats were defined on the basis of seat
stiffness (k) and frame rotation stiffness (j) for rearward occupant load. Stiff
seats have k=40 kN/m and j=1.8 degrees /kN representing a foreign benchmark
loaded by a male. One yielding seat had k=20 kN/m and j=1.4 degrees /kN
simulating a high-retention seat (1997 Grand Prix) and another k=20 kN/m and
j=3.4 degrees /kN simulating a 1980s to 1990s yielding seat (1990 Buick Park
Avenue). Constant vehicle acceleration for 100 msec gave delta-V of 6, 10, 16,
and 24 km/h. The one-dimensional model included a torso mass loading the
seatback with flexible neck and head mass. Based on biomechanical data and
scaling, neck stiffness was 5 kN/m and 3 kN/m for the male and female,
respectively. Based on validation tests, seat stiffness was 25% less with the
female. Occupant dynamics were simulated in a step-forward solution based on the
differential displacement between the head, torso, and seat up to head restraint
contact. Neck responses were 30% higher in the female than male through most of
the rear impact and are proportional to (kF/mTF)/(kM/mTM), which is the ratio of
seat stiffness divided by torso mass for the female and male. Neck displacements
were higher with the stiff seat than the 1990 C car seat for both the female and
male. They peaked at 10 km/h and dropped off for higher severity crashes due to
the shorter time to head contact. Neck displacements were greater in the female
than male for the lowest severity crashes with the stiff and 1990 C car seats,
when displacement was scaled for equal tolerance. The female in 1997 W car seat
had the lowest neck displacements. Stiff seats increased neck displacements over
the yielding seats of the 1980s in rear crashes. The trend is similar in men and
women, but early neck displacements are greater in women because of a higher
ratio of seat stiffness to torso mass. This implies that seat stiffness is not
sufficiently low in proportion to the female mass in comparison to males. The j
and k seat properties influence neck biomechanics and occupant dynamics, but k
is important in determining early response differences between males and
females.

PMID: 14522647 [PubMed - in process]



3: Traffic Inj Prev.  2003 Sep; 4(3): 214-27.  

Seat properties affecting neck responses in rear crashes: a reason why whiplash
has increased.

Viano DC.

ProBiomechanics LLC, Bloomfield Hills, Michigan 48304-2952, USA.
dviano@comcast.net

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.

PMID: 14522646 [PubMed - in process]



4: Annu Proc Assoc Adv Automot Med.  2003; 47: 383-98.  

A comparison of biomechanical mechanisms of whiplash injury from rear impacts.

Tencer AF, Huber P, Mirza SK.

Orthopedic Sciences Laboratory, University of Washington, Seattle, Washington,
USA.

Several hypotheses have been proposed to explain the mechanism of injury in
whiplash including, pressure on nerve root ganglia, stretching of facet
capsules, or damage to facet articular cartilage. These injury mechanisms have
not been directly compared in the same study. A comparison could provide insight
into the most likely mechanism of whiplash injury. Twenty eight volunteers
underwent rear impacts with head and chest acceleration data collected. The same
apparatus was used to test 11 cervico-thoracic human cadaveric spines with an
instrumented headform attached. Head acceleration, individual vertebral
kinematics from high speed video, local nerve root pressure, and facet joint
contact pressures were collected during impacts. Each specimen was tested first
at an impact acceleration similar to that of volunteers, who reported minimal or
no symptoms after the test, then at double the acceleration. Head X (forward)
and Z (upward) accelerations of cadaveric specimens were very similar in time
sequence and magnitude to those of unprepared volunteers. Pressure around the
lower cervical nerve roots ranged from 2.7kPa to 10kPa, and occurred generally
after chest but before peak head acceleration. Facets at C4-5 and C5-6 had the
highest probability (64% and 71% respectively) of pinching. Neither pressure
rise nor pinching changed significantly with increased acceleration. Vertebral
intersegmental extension rotations (4 ( o ) -9.5 ( o ) ) and posterior
translations (3.7-8.9 mm) peaked near maximum head excursion into the head
restraint, at the time of peak head acceleration. Vertebral shear translations
showed the largest (and only significant) increases with increased impact
acceleration. This data implies that facet shearing was most sensitive to the
increased acceleration in this experiment and may be a primary mechanism of
cervical spine injury in rear impacts.

PMID: 12941237 [PubMed - indexed for MEDLINE]



5: Annu Proc Assoc Adv Automot Med.  2001; 45: 187-201.  

Dynamic performances of different seat designs for low to medium velocity rear
impact.

Linder A, Olsson T, Truedsson N, Morris A, Fildes B, Sparke L.

Accident Research Centre, Monash University, Melbourne, Australia.

There is good evidence that seat design and impact severities in terms of
delta-V and acceleration plays a role in AIS 1 neck injury outcomes in the event
of a rear impact. This study evaluates a number of current production seats to
assess the AIS 1 neck injury protection potential at different impact
severities. Five different seat designs were exposed to four different impact
severities in a sled simulating a rear impact. The same delta-V produced with
different peak accelerations generated very different dummy responses. Head
restraint position influenced the angular and horizontal displacement of the
head relative to torso and the time of head to head restraint contact. The
lowest motion of the head relative to the torso was found in the two
anti-whiplash seats tested. The results of the study can be used for the design
of future vehicle seats and anti-whiplash systems.

PMID: 12214349 [PubMed - indexed for MEDLINE]



6: Accid Anal Prev.  2002 Mar; 34(2): 247-55.  

The neck injury criterion: future considerations.

Croft AC, Herring P, Freeman MD, Haneline MT.

Spine Research Institute of San Diego, Spring Valley, CA 91978, USA.
drcroft@san.rr.com

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 Bostrom et al. in 1996 (Bostrom 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 m2/s2 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.

PMID: 11829295 [PubMed - indexed for MEDLINE]



7: Spine.  2002 Jan 1; 27(1): 34-42.  

Internal loads in the cervical spine during motor vehicle rear-end impacts: the
effect of acceleration and head-to-head restraint proximity.

Tencer AF, Mirza S, Bensel K.

Department of Orthopedics, University of Washington, Seattle, USA.
atencer@u.washington.edu

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.

PMID: 11805633 [PubMed - indexed for MEDLINE]



8: Spine.  2001 Nov 15; 26(22): 2432-40; discussion 2441-2.  

The response of human volunteers to rear-end impacts: the effect of head
restraint properties.

Tencer AF, Mirza S, Bensel K.

Department of Orthopedics, University of Washington, Seattle, USA.
atencer@u.washington.edu

STUDY DESIGN: Human volunteers were subjected to a rear-end impact while sitting
on a standard automobile seat, and sagittal plane kinematic responses were
quantified. The effect of changing head restraint properties was determined by
use of a repeated measures design. OBJECTIVE: To determine the forces acting,
and relative motions resulting, on volunteers in a rear-end impact and the
effect of head restraint properties. SUMMARY OF BACKGROUND DATA: In several
recent studies of the kinematics of the cervical spine during rear-end impact, a
forward thrust to the lower cervical spine was produced, and a transient S shape
of the spine resulted while the head remained upright during the initial phase
of the impact. This may result in nonphysiologic intervertebral motions and
tissue strains. METHODS: Nineteen automobile seats were first tested, and a
modified head restraint was designed. Each volunteer sitting on a standard
vehicle seat was subjected to an impact pulse of 3g with a 4-kph speed change.
Testing was performed first with the modified head restraint, then again after
replacement by the head restraint that came with the seat. Kinematic responses
were compared for both head restraints by use of a repeated measures analysis of
variance. RESULTS: There was a measurable time difference between peak chest and
peak head accelerations, which resulted in the chest being thrust forward by the
seat back before the head was thrust forward by the head restraint. The modified
head restraint significantly reduced the contact time difference and therefore
decreased the relative chest-to-head forward motion. CONCLUSIONS: Volunteers
seated on a standard automobile seat demonstrated differential sagittal plane
motion between the chest and head. It is possible to significantly decrease the
relative chest-to-head motion by altering the characteristics of the head
restraint.

PMID: 11707705 [PubMed - indexed for MEDLINE]



9: J Trauma.  2001 Nov; 51(5): 959-69.  

The effectiveness of active head restraint in preventing whiplash.

Viano DC, Olsen S.

General Motors R&D Center, Warren, Michigan 48090-9055, USA. david.viano@gm.com

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.

PMID: 11706347 [PubMed - indexed for MEDLINE]



10: Annu Proc Assoc Adv Automot Med.  2000; 44: 299-308.  

Head trajectories of restrained child dummy in sled tests over 56 kph delta-v.

Hauschild HW.

Child restraint devices (CRDs) have been used for many years to protect children
in automotive crashes. The following data was collected to find out whether
current restraints would be able to pass more stringent dynamic testing at
higher changes in velocity (delta-v), such as the NHTSA NCAP program or the IIHS
offset barrier test, and to look at one possible misuse mode. Three basic types
of CRDs were sled tested at a delta-v between 57.5 & 61.4 kph (35.7 & 38.1 mph).
Data from each test are presented and compared. Comparisons are made between
each seat's sled test results and various countries' standards.

PMID: 11558089 [PubMed - indexed for MEDLINE]



11: Proc Inst Mech Eng [H].  2001; 215(2): 181-9.  

Computational studies of 'whiplash' injuries.

Gentle CR, Golinski WZ, Heitplatz F.

Department of Mechanical and Manufacturing Engineering, Nottingham Trent
University, Burton Street, Nottingham NG1 4BU, UK.

The term 'whiplash' was initially used to describe injuries to the neck caused
by the head being forced backwards during a rear-end collision in cars without
head restraints. The addition of head restraints in the 1970s was expected to
solve this problem by preventing excessive extension of the neck but experience
suggests the problem still exists. This paper reviews available experimental
studies of whiplash and uses the data to construct a finite element model which
is capable of dynamically simulating whiplash collisions and predicting the
forces in all the relevant neck ligaments. For the first time, it is shown that
trauma occurs long before the head hits the head restraint as a result of
displacement between the head and the torso caused by the head's inertia leading
to markedly different acceleration histories. It is concluded that experimental
and computational studies must be used together to produce progress in
biomechanical studies.

Publication Types:
    Review
    Review, Tutorial

PMID: 11382077 [PubMed - indexed for MEDLINE]



12: J Physiol.  2001 May 1; 532(Pt 3): 851-68.  

Variability in the control of head movements in seated humans: a link with
whiplash injuries?

Vibert N, MacDougall HG, de Waele C, Gilchrist DP, Burgess AM, Sidis A,
Migliaccio A, Curthoys IS, Vidal PP.

Laboratoire de Neurobiologie des Reseaux Sensorimoteurs, CNRS, ESA 7060, 45 rue
des Saints-Peres, 75270 Paris cedex 06, France. nivi@ccr.jussieu.fr

The aim of this study was to determine how context and on-line sensory
information are combined to control posture in seated subjects submitted to
high-jerk, passive linear accelerations. Subjects were seated with eyes closed
on a servo-controlled linear sled. They were asked to relax and received brief
accelerations either sideways or in the fore-aft direction. The stimuli had an
abrupt onset, comparable to the jerk experienced during a minor car collision.
Rotation and translation of the head and body were measured using an Optotrak
system. In some of the subjects, surface electromyographic (EMG) responses of
selected neck and/or back muscles were recorded simultaneously. For each
subject, responses were highly stereotyped from the first trial, and showed
little sign of habituation or sensitisation. Comparable results were obtained
with sideways and fore-aft accelerations. During each impulse, the head lagged
behind the trunk for several tens of milliseconds. The subjects' head movement
responses were distributed as a continuum in between two extreme categories. The
'stiff' subjects showed little rotation or translation of the head relative to
the trunk for the whole duration of the impulse. In contrast, the 'floppy'
subjects showed a large roll or pitch of the head relative to the trunk in the
direction opposite to the sled movement. This response appeared as an
exaggerated 'inertial' response to the impulse. Surface EMG recordings showed
that most of the stiff subjects were not contracting their superficial neck or
back muscles. We think they relied on bilateral contractions of their deep,
axial musculature to keep the head-neck ensemble in line with the trunk during
the movement. About half of the floppy subjects displayed reflex activation of
the neck muscles on the side opposite to the direction of acceleration, which
occurred before or during the head movement and tended to exaggerate it. The
other floppy subjects seemed to rely on only the passive biomechanical
properties of their head-neck ensemble to compensate for the perturbation. In
our study, proprioception was the sole source of sensory information as long as
the head did not move. We therefore presume that the EMG responses and head
movements we observed were mainly triggered by the activation of stretch
receptors in the hips, trunk and/or neck. The visualisation of an imaginary
reference in space during sideways impulses significantly reduced the head roll
exhibited by floppy subjects. This suggests that the adoption by the central
nervous system of an extrinsic, 'allocentric' frame of reference instead of an
intrinsic, 'egocentric' one may be instrumental for the selection of the stiff
strategy. The response of floppy subjects appeared to be maladaptive and likely
to increase the risk of whiplash injury during motor vehicle accidents.
Evolution of postural control may not have taken into account the implications
of passive, high-acceleration perturbations affecting seated subjects.

PMID: 11313451 [PubMed - indexed for MEDLINE]



13: Accid Anal Prev.  2001 May; 33(3): 289-304.  

Relationships between seat properties and human subject kinematics in rear
impact tests.

Welcher JB, Szabo TJ.

Biomechanical Research and Testing, Long Beach, CA 90815, USA.
welcher@scf.usc.edu

The mitigation of whiplash associated disorders (WAD) has received increased
priority in the last 10 years. Although the exact mechanism(s) for WAD causation
have not been established, several have been proposed and it is likely the
mechanism(s) are associated with the kinematics of the head relative to the
torso. It follows that automotive seat designs that address reductions in
certain head-torso kinematics may lead to a reduction in WAD potential. Seat
properties that may have an effect on head-neck kinematics include geometry,
stiffness and energy absorption. This study evaluated the performance of five
seats with varying properties, including the new Volvo 'WHIPS' seat. Seat
properties such as geometry relative to the occupant's head, dynamic and static
stiffness, and energy absorption were determined via component testing. A new
prototype dynamic seat test, which used a pendulum and seat back pan, was
evaluated. Human subject impact tests were conducted using three occupants in
rear impacts with velocity changes of 4 and 8 km/h. Potentially relevant
occupant kinematic parameters were identified, and then correlated with seat
properties in an attempt to determine any relative influence of seat properties
on potential WAD mechanisms. Two higher velocity human subject tests using the
Volvo Whiplash Injury Protection System (WHIPS) seat were also conducted.
Vertical and horizontal head to head restraint distances were found to be most
influential on occupant head-neck kinematics. Horizontal and vertical head to
head restraint offsets were significantly correlated with rearward translational
motion of the head center of gravity relative to the upper torso across all
occupants. Rearward offset was also significantly correlated with rearward
rotation of the head relative to upper torso, while vertical offset was
significantly correlated with head acceleration relative to the upper torso
during the flexion phase of the impact. Seat constitutive properties such as
stiffness and energy absorption were not significantly correlated with occupant
head-neck kinematics. The new dynamic seat test posed problems in data
interpretation, and suggestions for improvement are made. The Volvo 'WHIPS' seat
proved to be very effective in reducing many potential WAD associated head-neck
kinematics. The two increased severity impacts activated the additional
protective energy absorption elements in the seat, and no injuries were
sustained by the occupants.

Publication Types:
    Clinical Trial
    Randomized Controlled Trial

PMID: 11235791 [PubMed - indexed for MEDLINE]



14: Accid Anal Prev.  2000 Mar; 32(2): 299-305.  

Report investigating the importance of head restraint positioning in reducing
neck injury in rear impact.

Maher J.

Federal Office of Road Safety, Canberra ACT, Australia. jason.maher@dotrs.gov.au

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.

PMID: 10688486 [PubMed - indexed for MEDLINE]



15: Accid Anal Prev.  2000 Mar; 32(2): 287-97.  

Neck pain and head restraint position relative to the driver's head in rear-end
collisions.

Chapline JF, Ferguson SA, Lillis RP, Lund AK, Williams AF.

Insurance Institute for Highway Safety, Arlington, VA 22201-4751, USA.
iihs@highwaysafety.org

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.

PMID: 10688485 [PubMed - indexed for MEDLINE]



16: Accid Anal Prev.  2000 Mar; 32(2): 251-60.  

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

Eichberger A, Darok M, Steffan H, Leinzinger PE, Bostrom O, Svensson MY.

Institute for Mechanics, University of Technology, Graz, Austria.
arno.eichberger@sft.steyr.com

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 therefore 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.

PMID: 10688481 [PubMed - indexed for MEDLINE]



17: Accid Anal Prev.  2000 Mar; 32(2): 219-32.  

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

Lawrence JM, Siegmund GP.

MacInnis Engineering Associates, Richmond, BC, Canada. jonl@maceng.com

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

PMID: 10688478 [PubMed - indexed for MEDLINE]



18: Accid Anal Prev.  2000 Mar; 32(2): 177-85.  

Comment in:
    Accid Anal Prev. 2001 Sep;33(5):685-6.

Whiplash injury--are current head restraints doing their job?

Minton R, Murray P, Stephenson W, Galasko CS.

Transport Research Laboratory, Crowthorne, Berkshire, UK. rminton@trl.co.uk

It is generally accepted that the incidence of whiplash associated disorders is
increasing in all industrialised countries, despite the almost universal fitment
of head restraints in at least the front seats of cars. This is usually
attributed to the fact that few people can be observed to follow the standard
recommendations as regards head restraint positioning, that is, level with the
head vertically and as close to the head as possible horizontally. This study
set out to determine whether any other factors, in addition to head restraint
adjustment, could be found which would influence the severity of whiplash
injury. This was done by linking medical assessment of real-world accident
victims with engineering assessment of the accident vehicles. A random sample of
road accident victims suffering from whiplash associated disorder was studied.
The vehicles they had been travelling in were examined to assess impact severity
and, where possible, measurements were made of seat and head restraint
adjustment with the subject sitting in the vehicle. All subjects were
interviewed to assess the disability resulting from their injuries, and their
progress was followed for 12 months. The results were subjected to statistical
analysis to try to determine relationships between severity of injury (as
measured by resultant disability) and a number of occupant- and vehicle-related
factors. A significant proportion of the sample had suffered lumbar strain
injury in addition to whiplash, and these were excluded from the present
analysis. Frontal impact victims suffered symptoms indistinguishable from those
of rear impact victims. The beneficial effects of good head restraint adjustment
could not be clearly demonstrated, and some trends, especially in rear impacts,
where the benefits of a well-adjusted restraint should have been very clear,
indicated that larger distances from head to restraint were associated with
lower disability. The paper discusses these counter-intuitive results and their
implications.

PMID: 10688474 [PubMed - indexed for MEDLINE]



19: Accid Anal Prev.  2000 Mar; 32(2): 143-50.  

Head restraints--the neglected countermeasure.

O'Neill B.

Insurance Institute for Highway Safety, Arlington, VA 22201-4751, USA.
iihs@highwaysafety.org

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.

PMID: 10688470 [PubMed - indexed for MEDLINE]



20: Accid Anal Prev.  1999 Jul; 31(4): 393-407.  

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

Siegmund GP, Heinrichs BE, Wheeler JB.

MacInnis Engineering Associates, Richmond, BC, Canada. gunters@maceng.com

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

Publication Types:
    Clinical Trial
    Randomized Controlled Trial

PMID: 10384232 [PubMed - indexed for MEDLINE]



21: Accid Anal Prev.  1998 Nov; 30(6): 773-80.  

Motivating drivers to correctly adjust head restraints: assessing effectiveness
of three different interventions.

Fockler SK, Vavrik J, Kristiansen L.

Research Services, Insurance Corporation of British Columbia, North Vancouver,
Canada.

Three types of driver educational strategies were tested to determine the most
effective approach for motivating drivers to adjust their head restraints to the
correct vertical position: (1) a human interactive personal contact with a
member of an ICBC-trained head restraint adjustment team, (2) a passive video
presentation of the consequences of correct and incorrect head restraint
adjustment, and (3) an interactive three-dimensional kinetic model showing the
consequences of correct and incorrect head restraint adjustment. An experimental
pretest-posttest control group design was used. A different educational
treatment was used in each of three lanes of a vehicle emissions testing
facility, with a fourth lane with no intervention serving as a control group.
Observational and self-reported data were obtained from a total of 1,974
vehicles entering and exiting the facility. The human intervention led to
significantly more drivers actually adjusting their head restraints immediately
after the intervention than the passive video or interactive kinetic model
approaches, which were both no different from the control group. The human
intervention was recommended as the most effective and was implemented
successfully on a limited basis during 3 months of 1995 and again during 3
months of 1996.

Publication Types:
    Clinical Trial
    Randomized Controlled Trial

PMID: 9805520 [PubMed - indexed for MEDLINE]



22: Unfallchirurg.  1997 Jul; 100(7): 561-7.  

[Automobile head supports--adjustment possibilities and utilization. Results of
a field study]

[Article in German]

Jerosch J, Ruth S, Thorwesten L.

Orthopadische Klinik Munchen Harlaching.

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.

PMID: 9340782 [PubMed - indexed for MEDLINE]



23: Accid Anal Prev.  1996 Mar; 28(2): 221-7.  

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

Svensson MY, Lovsund P, Haland Y, Larsson S.

Department of Injury Prevention, Chalmers University of Technology, Goteborg,
Sweden. mys@ip.chalmers.se

The influence of different seat properties on the head-neck motion during a
low-velocity rear-end impact was tested using a Hybrid III-dummy fitted with a
modified neck (RID-neck). The results show that by modifying the properties of
the seat-back and head-restraint it is possible to influence the head-neck
kinematics to a great extent. It was possible to virtually eliminate the neck
extension motion during a rear-impact. This will hopefully result in a
significant decrease in neck injury risk in real world rear-impacts.

PMID: 8703280 [PubMed - indexed for MEDLINE]



24: J Neurol.  1995 Jul; 242(7): 443-9.  

The effect of accident mechanisms and initial findings on the long-term course
of whiplash injury.

Sturzenegger M, Radanov BP, Di Stefano G.

Department of Neurology, University of Berne, Inselspital, Switzerland.

The aim of this study was to assess the relationships between accident
mechanisms as well as initial findings and the long-term course of whiplash
injury. A representative sample of 117 consecutive patients referred by primary
care physicians was followed-up over 12 months., Fractures or dislocations of
the cervical spine, head trauma and pre-existing neurological disorders were
exclusion criteria. The interval between the accident and the baseline
examination was 7.4 days (SD 4.2 days). Assessment included accident features
(e.g. passenger position in the car, head restraint, head position, type of
collision), initial symptoms (e.g. intensity and onset of pain, symptoms of
neurological dysfunction, multiple symptom score), and signs (restricted neck
movement, neurological deficits). At the 1-year examination, patients were
divided into an asymptomatic and a symptomatic group and were compared with
respect to accident features and baseline findings. Twenty-four percent of
patients were still symptomatic after 1 year. Analysing accident mechanisms
separately, rotated or inclined head position was the primary feature related to
symptom persistence (P = 0.005). The symptomatic group scored higher at baseline
on the multiple symptom rating (P = 0.004) and had a higher incidence of initial
headache (P = 0.004) and neurological symptoms (P = 0.008) together with a
higher intensity of headache (P = 0.0002) and neck pain (P = 0.0009).(ABSTRACT
TRUNCATED AT 250 WORDS)

PMID: 7595675 [PubMed - indexed for MEDLINE]



25: Orthopade.  1994 Aug; 23(4): 262-7.  

[Biomechanical aspects of injuries of the cervical vertebrae]

[Article in German]

Walz F.

Institut fur Rechtsmedizin, Universitat Zurich-Irchel.

A biomechanical expert opinion on the injury mechanism is necessary only in a
few cases. However, the judgement of these cases is extremely compromised if the
mechanics of injury are described incorrectly in the clinical report. Since the
mechanism of neck injuries is very complex, the physician without biomechanical
training should concentrate on the familiar clinical findings; The relevant
mechanisms of indirect neck trauma are (a) a non-head-contact mechanism
(hyperflexion or hyperextension, hypertranslation, acceleration) and (b) head
contact leading to compression, hyperflexion, hyperextension and/or
hypertranslation. A non-head-contact mechanism occurs, for example, in the case
of rear end impact without head restraint (hyperextension) or a frontal
collision involving a belted occupant (hyperflexion), without head impact. The
term "whiplash" is misleading and incorrect: It presumes a virtually
non-existent two-phase movement back and forth (or vice versa), and it confuses
the physical criterion mechanism and the anatomical or morphological criterion
injury, e.g. distortion, sprain etc. A head-contact mechanism involves momentum
exerted from the head on the neck. Again, the anatomical and morphological terms
are the same, but the mechanism is different. With a contact mechanism and a
non-contact mechanism, not only a hyperflexion or a hyperextension can occur; in
the first phase of the impact, a shearing force between the upper vertebral
bodies (C0-C2) may load the intervertebral structures by hypertranslation.

Publication Types:
    Review
    Review, Tutorial

PMID: 7970681 [PubMed - indexed for MEDLINE]



26: Z Unfallchir Versicherungsmed.  1994 Jul; 87(2): 71-85.  

[Biomechanical aspects of cervical trauma]

[Article in French]

Walz F, Meine J.

Institut fur Rechtsmedizin, Universitat Zurich-Irchel.

The biomechanical expert opinion on the injury mechanism is necessary in few
cases only. However, the judgement of these cases is extremely compromised if
mechanically wrong terms are introduced in the clinical report. Since the injury
mechanism in the neck is very complex the clinical physician should concentrate
on the clinical findings familiar to him; usually the clinician lacks technical
case documentation and specific training in injury biomechanics. The relevant
mechanisms of neck injuries are an indirect trauma induced by a) a head contact
leading to compression, hyperflexion, hyperextension and/or hypertranslation and
b) a non-head-contact mechanism (hyperflexion or hyperextension,
hypertranslation, acceleration). A non-contact mechanism occurs e.g. during a
rear end impact without head restraint (hyperextension) or a frontal collision
of a belted occupant (hyperflexion) without head impact. The term "whiplash" is
misleading and incorrect: It presumes a virtually non existing two phase
movement back and forth (or vice versa) like during the development of the crack
of the whip. Secondly, it mixes the physical criterion mechanism with the
anatomical or morphological criterion injury e.g. distortion, sprain etc. A
(head)-contact mechanism is due to a corresponding momentum exerted from the
head on the neck. Again, the anatomical or morphological terms are equal, but
the mechanism is different. During a contact mechanism as well as during a
non-contact mechanism not only a hyperflexion or a hyperextension can occur; in
the first phase of the impact also a shearing force between the upper vertebral
bodies (CO-C2) may load the intervertebral structures by hypertranslation.

PMID: 7946696 [PubMed - indexed for MEDLINE]



27: Neurology.  1994 Apr; 44(4): 688-93.  

Presenting symptoms and signs after whiplash injury: the influence of accident
mechanisms.

Sturzenegger M, DiStefano G, Radanov BP, Schnidrig A.

Department of Neurology, University of Berne, Switzerland.

OBJECTIVE: To assess the relationship between accident mechanisms and initial
findings after whiplash injury. DESIGN: Cohort study. SETTING: Outpatient
department, Department of Neurology, University of Berne, Switzerland. PATIENTS:
A population-based sample of 137 consecutive patients referred by primary care
physicians. Fractures or dislocations of the cervical spine, head trauma, and
preexisting neurologic disorders were exclusion criteria. MAIN OUTCOME MEASURES:
Patients were interviewed and examined within 7.2 days (SD, 3.9 days) after
trauma. Analyzed accident features were position in the car, use of seat belt,
head restraint and its point of head contact, damage to seat, head position and
state of preparedness at the moment of impact, and type of collision. Analyzed
symptoms were intensity and onset delay of post-traumatic head and neck pain;
pain in the shoulders, back, and anterior neck; symptoms of neurologic
dysfunction according to presumed origin--cranial nerve or brainstem, radicular
or myelopathic; and a score of multiple symptoms. Analyzed signs were neck
muscle tenderness and restricted neck movement, and signs of cranial nerve,
brainstem, or radicular dysfunction. RESULTS: Passenger position in the car, use
of seat belt, and the presence of a head restraint showed no significant
relationship with findings. Rotated or inclined head position at the moment of
impact was associated with a higher frequency of multiple symptoms (p = 0.045
and 0.008) with more severe symptoms and signs of musculoligamental cervical
strain (p = 0.048 and 0.038) and of neural, particularly radicular (p = 0.031
and 0.019), damage. Unprepared occupants had a higher frequency of multiple
symptoms (p = 0.031) and more severe headache (p = 0.046). Rear-end collision
was associated with a higher frequency of multiple symptoms (p = 0.006),
especially of cranial nerve or brainstem dysfunction (p = 0.00003). CONCLUSION:
Three features of accident mechanisms were associated with more severe symptoms:
an unprepared occupant; rear-end collision, with or without subsequent frontal
impact; and rotated or inclined head position at the moment of impact.

PMID: 8164827 [PubMed - indexed for MEDLINE]