Thanks to
Insurance Institute for Highway Safety
for permission to reproduce this page!
Q&A:
NECK INJURY
as of March 2004
- What is whiplash?
- What happens to an occupant when their vehicle is
struck from the rear?
- How common are neck injuries? Are
motorists susceptible to neck injuries in all crash configurations?
- Why does my vehicle have a headrest? Are there restraint
standards?
- How should my head restraint be positioned?
- How good are the head restraints on passenger vehicles?
- Are the Institute's restraint ratings reflected
in real world crashes?
- What factors influence the severity of neck injury?
- What restraint improvements can be expected in the future?
- Is there
any evidence head restraint improvements are effective in reducing
neck injuries?
1.
What is whiplash? Whiplash and whiplash-associated disorders (WAD)
are terms used to describe a range of neck injuries that are related
to sudden distortions of the neck. The most common symptom whiplash
victims report is pain due to mild muscle strain or minor tearing
of soft tissue. Other injuries include nerve damage, disc damage,
and in the most severe cases, ruptures of ligaments in the neck and
fractures of the cervical vertabrae. Generally, minor whiplash injuries
are associated with pain and decreased range of motion in the head
and neck. These symptoms usually last only a short time, but occasionally
they last longer and include headaches, dizziness, and tingling in
the arms. People experiencing whiplash injuries report symptoms that
last from a few hours to several years with the vast majority experiencing
short-term symptoms of pain. The physical injury to create symptoms
of whiplash is uncertain. It is suspected that the biological cause
of long-term whiplash symptoms is nerve damage while short-term pain
may be a minor strain or sprain.
It
is known that people can experience severe crashes with no neck injury
if there is little or no movement of the head relative to the
torso. Consequently, neck distortion resulting from sudden movement
of the head relative to the torso probably explains most whiplash
injuries. Hyperextension of the neck, or distortion beyond its normal
range of
motion, may explain many whiplash injuries, but experimental and
field studies suggest that nerve damage and its associated long-term
symptoms
can occur with milder levels of neck distortion. One hypothesis that
explains these nerve injuries is based on damage to the nerves in
the joints caused by motion of adjacent neck vertebrae during a crash.1 Another
hypothesis suggests that the nerve damage is caused by fluctuation
in spinal fluid pressure arising from neck distortions.2
2.
What happens to an occupant when their vehicle is struck from
the rear? While whiplash injuries are common in all types of crashes,
motorists involved in rear-end crashes are more likely to experience
whiplash. When a vehicle is struck from the rear it is accelerated
forward, causing the seatback to push against the occupant's
torso and propel it forward. The head lags behind the torso until the
neck reaches its limit of distortion, then the head is suddenly accelerated
by the neck much like the tip of a whip, hence the term whiplash. Head
restraints limit the neck distortion that occurs before the head starts
to follow the torso.
3.
How common are neck injuries? Are motorists
susceptible to neck injuries in all crash configurations? In
the United States, neck sprains and strains are the most frequently
reported injury
in insurance claims. In 1997, it is estimated that 66 percent
of all insurance claimants under bodily injury liability coverage
and 59 percent under personal injury protection coverage --
the two most important insurance injury coverages -- reported
a minor neck injury. For 42 and 36 percent of injury claimants,
respectively, neck sprains or strains was the most serious
injury reported. The cost of just these injury claims where
neck pain was the most serious was $7 billion.3
Whiplash
injuries can occur in any kind of crash but occur most often in rear-end
collisions. A 1999 Institute study found that 26 percent of rear-struck
vehicle drivers reported neck injuries.4 This
was essentially the same as the 24 percent neck injury rate reported
in a 1972 Institute
study.5 Estimates of neck injury
rates in other studies have ranged from 7 to 37 percent, depending
on whether police or motorists reported
the information.6,7,8
4.
Why does my vehicle have a headrest? What many motorists refer
to as a headrest is actually a head restraint. It is a common misconception
that a restraint is a comfort feature and this simply is not true.
Head restraints are installed in vehicles for safety purposes and are
an essential safety feature like lap/shoulder belts. Effective head
restraints reduce the rearward motion of an occupant's head in
a rear-end crash and decrease the likelihood of sustaining a whiplash
injury. A recent 2002 Public Attitude Monitor asked participants what
the main purpose of a head restraint was and 67 percent correctly
identified safety while 13 percent said comfort and another 15
percent didn't know.9
Are
there restraint standards? Yes, since January 1, 1969,
the National Highway Traffic Safety Administration under FMVSS
(Federal Motor Vehicle Safety Standard) No. 202 has mandated head
restraints
in the front outboard seats of all new passenger cars. On September
1, 1991, head restraint standards were extended to pickups, vans
and SUVs. The restraints installed by manufacturers
must extend
at least 27.5 inches above the seating reference point (a point
slightly above and in front of where the seat and seatback meet)
when in their
highest (up) positions. Even at this height the restraint isn't
high enough for many occupants. Many motorists do not adjust their
restraints yet there is no regulation dictating a minimum height
for restraints in the lowest (down) position in the United States.
The
European Economic Community followed the United States and mandated
head restraints in the late 1970s. Recently the European Union
adopted more stringent standards. Effective in 1998 head restraints
have to
be at least 29.5 inches in the lowest position and exceed 31.5
inches in the highest position. The United States proposed in
2001 to upgrade
its standard but the rule has not yet been finalized. In the meantime,
two types of restraints satisfy the current requirements. The first
is an integral head restraint; this design has a seatback that
is high enough to meet the head restraint height requirement.
The second is
an adjustable head restraint, which consists of a cushion that
is attached to the seatback by sliding metal shafts. Adjustable
restraints can
be moved and sometimes locked into different heights; some can
also be adjusted horizontally to change the distance between
the head and
restraint. Manufacturers may install either integral
or adjustable restraints.
5.
How should my head restraint be positioned? To reduce the likelihood
of sustaining a whiplash injury in a crash, neck distortion must be
kept to a minimum. Well-designed and properly positioned head restraints
are essential to whiplash prevention. A head restraint should be positioned
at least level with the top of the ears or about 3.5 inches below the
top of the occupant's head. The distance from the back of the
head to the restraint should be as small as possible, preferably less
than four inches. Because motorists differ in height, the amount of
adjustment needed varies. For some occupants no adjustment from the
downward position is required.
6.
How good are the head restraints on passenger vehicles? The Institute
regularly evaluates the geometry of head restraints in hundreds of
new passenger vehicles and has been doing so since 1995. Each restraint
is classified into one of four geometric zones defined by its height
and backset (distance from the back of an occupant's head to
the front of the restraint). Restraints are rated as good, acceptable,
marginal, or poor. The measurements are made with a dummy representing
an average-size male at a typical seatback angle. Head restraints have
improved since the surveys began. In 1995 only 3 percent of measured
head restraints rated good compared with 45 percent in 2003. The number
of poor
restraints has decreased dramatically from 82 percent in 1995 to 10
percent in 2003. These ratings are a good indicator of the proportion
of motorists likely
to be protected in a rear-end crash. Marginal head restraints are not
more than 4.5 inches from the back of the dummy's head and are
tall enough to protect average-size males and shorter motorists from
injury. Restraints rated acceptable and good can protect taller motorists.
7.
Are the Institute's restraint ratings reflected in real world
crashes? Yes, Institute ratings are related to how well people are
protected in real world rear-end crashes. The Institute analyzed more
than 5,000 insurance claims and determined that, all other factors being
the same, drivers with restraints rated good are 24 percent less likely
than drivers with poor head restraints to sustain neck injuries in rear-end
crashes. In vehicles with restraints rated as acceptable, insurance claims
for neck pain were lower for females but not for males. This may be because
females in general are shorter than males, allowing a restraint in the
down position to offer some protection to women.4 A
second Institute study conducted in Rochester, New York, surveyed 585
drivers who had
been in
rear-end crashes. Measurements were taken while each driver assumed a
normal driving posture with their restraint in the position it was during
the crash. The findings showed that head restraints positioned at or
above the head's center of gravity could reduce reported neck pain
after a rear-end crash. Drivers with such head restraints reported 40
percent fewer instances of neck pain than those with poorly positioned
restraints.10
8.
What factors influence the severity of neck injury?
Height: Height
is a risk factor, particularly among women, according to recent
German research.11 Often times shorterindividuals are protected by an unadjusted head restraint.
Stature may not play a role in the severity of injury to men because
many head restraints are too low to offer even shorter men protection.
Taller
motorists who don't adjust their head restraints are more likely
to sustain whiplash injuries.
Gender: The
same German report also found women to be 1.8 to 2.2 times more
at risk of neck injury in all types of collisions, a finding
that is consistent with research by the Institute and other organizations.
In addition, a Swedish study found that women with whiplash
injuries
are more likely to develop long-term symptoms of whiplash
than are men with whiplash. Fifty-five percent of the women who
sustained
whiplash injuries went on to develop long-term symptoms compared with
38 percent of men.12 One possible explanation is that men have
more neck musculature
than women for about the same size head. Another hypothesis
is that
women tend to sit farther away from their seatbacks than
men, thus their heads travel farther to the rear in a crash before
reaching
a
head restraint.
Seating
position: It is uncertain which seating position
exposes an occupant to a greater chance of sustaining a neck
injury. One
study concluded drivers have a higher risk rate than passengers.
It was hypothesized that drivers are prone to move forward
and away from the seatback as they reach for the steering
wheel and
observe traffic around them, whereas passengers are usually
more relaxed and lean further back in their seats, with their
heads
close to the restraint. Occupants seated in the back seat
rather than the front, are also less likely to sustain a
neck injury.13
A
more recent study indicates a higher disability risk
from neck
injury for females than for males in any seating position.
For females, the disability risk is lowest in the front
passenger seat. The risk is significantly higher for females
in the rear passenger seat. For men, there is a small
difference between the front seat occupants, while the risk decreases
from
the front seat to the rear seat. The disability risk
in the driver seat is three times higher for
females than for males, and four times higher for females
in the
rear seat.14
9.
What restraint improvements can be expected in the future? After
years of neglect, improved head restraints are beginning to appear. Some
auto manufacturers include head restraints that automatically adjust
position when the seat is adjusted. Tall occupants who adjust the seat
rearward to gain leg room also gain the added protection of a higher
head restraint. Other manufacturers have incorporated 'active' systems
that automatically improve head restraint position during a crash. For
example, the Saab Active Head Restraint and General Motors Catcher's
Mitt designs include head restraints attached to a lever arm in the seatback
that moves the restraint up and forward as the occupant's back
pushes into the seatback. Volvo's WHIPS -- or whiplash injury prevention
system seat - combines good head restraint geometry with a special seatback
hinge that gently accelerates the seat occupant's torso, thus giving
the head restraint time to catch the head before neck distortions become
too severe.
Volvo
WHIPS seat:
Saab Active Head Restraint
10.Is
there any evidence head restraint improvements are effective
in reducing neck injuries? Recently the Institute gathered
data from Nationwide, Progressive, and State Farm insurance companies
to look at improved
seat design in rear-end
crashes. More than 2,000 property damage liability claims were
identified involving selected vehicles. The vehicles studied
were the Ford
Taurus and Mercury Sable models with improved head restraint
geometry, Volvo S70s with WHIPS (Whiplash Injury Prevention System),
Toyota
and Lexus models with the WIL (Whiplash Injury Lessening)
system plus a
number of Buick, Nissan, Pontiac, and Saab models with active
head restraints. The rates of insurance claims for driver neck
injuries
in the rear-end
crashes were compared before and after the seat and head restraint
design changes. A 43 percent reduction in neck injury claim
rates was seen for the Saab, General Motors, and Nissan models
with
active head
restraints, compared with similar cars before such restraints
were introduced. Similar before/after comparisons of Volvos and
Fords
showed reductions in claim rates. A 49 percent reduction
was seen in Volvos compared with an 18 percent reduction in the Fords with improved
geometry. The Toyota WIL system did not show any reduction in
neck injuries.15
References
1
Ono,
K. and Kaneoka, K. 1997. Motion analysis of human cervical
vertebrae during low-speed rear impacts by the simulated sled.
Proceedings of the 1997 International IRCOBI Conference
on the Biomechanics of Impact, 223-237. Bron, France: International
Research Council on the Biokinetics of Impacts.
2
Svensson,
M.Y.; Aldman, B.; Lövsund, P.; Seeman, T.;
Suneson, A.; and Örtengren. 1993. Pressure effects in
the spinal canal during whiplash extension motion -- a possible
cause of injury to the cervical
spinal ganglia. Proceedings of the 1993 International Conference
on the Biomechanics of Impacts, 189-200. IRCOBI, Lyon,
France.
3
Insurance
Research Council. 1999. Injuries in auto accidents. Malvern,
PA: Insurance Research Council.
4
Farmer,
C.M.; Wells, J.K.; and Werner, J.V. 1999. Relationship of head
restraint positioning to driver neck injury in
rear-end crashes. Accident Analysis and Prevention, 31:
719-728.
5
O'Neill,
B.; Haddon, W.; Kelley, A.B.; and Sorenson, W.W. 1972. Automobile
head restraints -- frequency of
neck injury claims in relation to the presence of head
restraints. American Journal of Public Health 62: 309-406.
6
Braunstein,
P.W. and Moore, J.O. 1959. The fallacy of the term 'whiplash'
injury. American
journal of surgery,
97: 522-529.
7
Quinlan,
K.P.; Annest, J.L.; Myers, B.; Ryan, G. and Hill, H. 2004.
Neck strains and sprains among
motor vehicle
occupants -- United
States, 2000. Accident Analysis and Prevention 36:
21-27.
8
States,
J.D.; Balcerak, J.C.; Williams, J.S.; Morris, A.T.; Babcock,
W.; Polvino, R.; Riger,
R.; and Dawley,
R.E. 1972.
Injury frequency and head restraint effectiveness
in rear-end impact
accidents. Proceedings of the 16th Stapp
Car Crash Conference, 228-245.
9
Insurance
Research Council. 2002. Public Attitude Monitor 2002.
10
Chapline,
J.F.; Ferguson, S.A.; Lilis, R.P.; Lund, A.K.; and Williams,
A.F. 2000.
Neck pain
and head restraint
position
relative to the driver's head in rear-end
collisions. Accident Analysis and Prevention 32(2): 287-297.
11
Temming,
J. and Zobel, R. 1998. Frequency and risk of cervical spine
distortion injuries
in passenger
car accidents: significance
of human factors data. Proceedings
of the International Conference on the
Biomechanics
of Impact 219-233.
Goteborg,
Sweden, IROCBI.
12
Krafft,
M. 1998. A comparison of short- and long-term consequences
of AIS 1 neck injuries, in rear impacts.
Proceeding of the International Conference on the Biomechanics
of Impact, 235-248. Goteborg, Sweden, IRCOBI.
13
Lundell,
B.; Jakobsson, L.; Alfredsson, B.; Jernstrom, C.; and Isakkson-Hellman,
I. 1998. Guidelines for and the design
of a car seat concept for improved protection against neck
injuries
in rear end car impacts. SAE Technical Paper Series 980301.
Detroit, MI: International Congress and Exposition.
14
Krafft,
M.; Kullgren, A.; Lie, A.; and Tingvall, C. 2003. The risk
of whiplash injury in the rear seat compared to the
front seat in rear impacts. Traffic Injury Prevention 4:
136-140.
15
Farmer,
C.M.; Wells, J.K.; and Lund, A.K. 2003. Effects of head restraint
and seat redesign on neck injury risk in
rear-end
crashes. Traffic Injury Prevention 4: 83-90.
©1996-2004, Insurance Institute for Highway Safety, Highway Loss Data Institute
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