By Matthew J. DeGaetano, DC and James D. Atkinson, DC
One countermeasure continues to make a measurable difference when it comes to preventing neck strains and sprains when an occupant’s vehicle is rear-ended in traffic, a new IIHS-HLDI study of insurance claims indicates. Seat/head restraint combinations that earn the top rating of good in IIHS tests reduce injury claim rates by 11 percent compared with vehicles with poor-rated seats/head restraints. What is more, women and younger occupants appear to be enjoying the biggest benefits.
The analysis updates and expands on prior research by IIHS and HLDI indicating that seat/head restraint combinations that earn good ratings in IIHS tests reduce the chances that drivers will sustain neck injuries if their vehicles are rear-ended (see “Neck injury risk is lower if seats and head restraints are rated good,” March 15, 2008). IIHS rates vehicles good, acceptable, marginal, or poor based on both front-seat head restraint geometry and test results (see Status Report special issue: protection against neck injury, Nov. 20, 2004). IIHS added a dynamic test in 2004.
A decade ago, more than half of the seats/head restraints IIHS evaluated were rated poor and only 9 percent were rated good. Now, 95 percent of 2015 models are rated good, and none are rated poor. This is largely due to the Institute’s ratings program and an upgraded U.S. regulation requiring front-seat head restraints to be higher and closer to the back of people’s heads in all new vehicles as of September 2010.
“The latest findings show that seat/head restraint combinations that rate good in IIHS evaluations are helping to reduce the overall injury rate in crashes,” says David Zuby, IIHS chief research officer and one of the co-authors of the new study.
Analysts examined an insurance claim database of more than 600,000 rear-impact crashes to determine the likelihood of an associated injury claim. Results were based on 2001-14 model year cars and SUVs using property damage liability and personal injury protection claims. Property damage liability covers damage caused by the insured vehicle to someone else’s vehicle or property. Personal injury protection coverage is sold in states with no-fault insurance systems and covers injuries to occupants of the insured vehicle regardless of who is at fault.
The injury-reduction benefits were greatest for good-rated seats/head restraints. Those with acceptable or marginal ratings had injury rates that were 4.4 percent and 3.7 percent lower, respectively, than seats/head restraints rated poor.
Zuby points out that the database doesn’t contain information on exactly who in the vehicle was injured — for example, whether they were the driver — or the type of injury. Prior studies indicate that neck sprains and strains, or whiplash, are the most frequently reported injuries to insurers. Most often these injuries occur in rear-end collisions, but they can happen in other types of crashes, too.
When a vehicle is struck in the rear and pushed forward, occupants’ torsos move forward with their seats. If a person’s head isn’t supported by a head restraint, the head lags behind the torso, and the differential motion causes the neck to bend and stretch. The higher the torso acceleration, the more sudden the motion, the higher the forces on the neck, and the more likely a neck injury is to occur.
The key to reducing whiplash injury risk is to move the head and torso together. To accomplish this, the geometry of a head restraint has to be adequate — high enough and near the back of the head. Then the seat structure and stiffness must be designed to work in concert with the head restraint to support an occupant’s neck and head, accelerating them with the torso as the vehicle is pushed forward. That’s why good head restraints are so important.
Analysts broke down benefits by the gender and age of the rated driver on the insurance policy and examined rear crashes that resulted in more-severe injury claims (higher than $2,000). The gender and age analysis is based on the characteristics of the rated driver, the person assigned to the vehicle for insurance purposes but not necessarily driving at the time of a crash.
Women fared better than men in the study, with lower injury rates for good, acceptable and marginal-rated seats compared with poor-rated seats. For males, only good-rated seats were associated with statistically lower injury rates. Injury rates were 13 percent lower for women and 9 percent lower for men in vehicles with good-rated seats/head restraints.
This greater reduction in injuries for females is encouraging since earlier studies have shown that neck injuries are more likely among women in rear impacts than men.
Rated driver age also affects injury outcomes. In the study, good-rated seats had lower injury rates than poor-rated seats in vehicles with drivers in age groups 15-24, 25-44 and 45-64. Drivers ages 15-24 had the largest reduction at 20 percent, followed by ages 45-64 at 11 percent, and ages 25-44 at 10 percent.
The results for more serious injuries followed a similar pattern among gender and age groups. Looking at crashes involving claims of $2,000 or more, analysts found 16 percent fewer insurance claims were filed for neck injuries among females in vehicles with good-rated seats/head restraints compared with people in vehicles with poor seats/head restraints. Looking at age groups, drivers 25-44 years old and 46-64 years old had the largest reductions in injury rates when comparing good-rated seats/head restraints and poor-rated seat/head restraint combinations.
The term “whiplash” is used to describe a variety of neck injuries that often occur in rear-end crashes. The most common of these are mild muscle strain and minor tearing of soft tissue. Other injuries include nerve damage, disk damage and, in the most severe cases, ruptures of ligaments in the neck and fractures of the cervical vertebrae. Nerve damage, which can occur even when other injuries are mild, is probably responsible for long-term symptoms, such as headaches, dizziness and ringing in the ears.
Neck distortion resulting from sudden movement of the head relative to the torso is believed to explain most whiplash. Specifically, hyperextension of the neck, or rearward bending beyond its normal range of motion, likely causes many injuries. People can experience severe crashes with no neck injury if there is little or no movement of the head relative to the torso.
However, experimental and field studies suggest that even slight neck bending that falls well short of hyperextension can cause nerve damage. One hypothesis is that such damage is caused by motion of adjacent neck vertebrae during a crash. 1 Another hypothesis is that it is caused by fluctuation in spinal fluid pressure arising from neck distortions. 2
How Does Whiplash Happen?
Whiplash is most commonly received from riding in a car that is struck from behind, or collides with another vehicle. When the head is suddenly jerked back and forth beyond its normal limits, the muscles and ligaments supporting the spine can be over-stretched or torn. In a rear end collision for example, the victim’s car is first pushed or accelerated forward and then, because their foot is on the brake, or their car hits the vehicle in front, their car is rapidly slowed down, or decelerated. As the vehicle accelerates forward, it pushes the body forward too, but the head remains behind momentarily, rocking up and back, until some of the muscles and ligaments are stretched or torn.
Muscles, are in a reflex action, contract to bring the occupant’s head forward again, and to prevent excessive injury. This overcompensates because at this point the head is already traveling in a forward direction as the car decelerates. This violently rocks the head forward, stretching and tearing more muscles and ligaments. The soft pulpy discs between the vertebrae can bulge, tear, or rupture. Vertebrae can be forced out of their normal position, reducing range of motion. The spinal cord and nerve roots get stretched, irritated, and choked. If the victim is not properly restrained the occupants head may strike the steering wheel or windshield, possibly causing a concussion.
Conservative treatment includes immobilizing the patient’s neck in a well-fitting soft cervical collar; use of pain, anti-inflammatory, and muscle relaxant medications; and chiropractic and physical therapy.
Whiplash is a sudden movement of the head, backward, forward, or sideways. Whether from a car accident, sports, or an accident at work, whiplash or other neck injuries warrant a thorough chiropractic check-up. The biggest danger with whiplash injuries is that the symptoms can take years to develop. Too often people don’t seek treatment until more serious complications develop. Even after whiplash victims settle their insurance claims, some 45% report they still suffer with symptoms two years later.
Neck sprains and strains are the most frequently reported injuries in U.S. auto insurance claims. Such whiplash injuries can be sustained in any type of crash but occur most often in rear-end collisions. Good head restraints can help prevent them.
Insurance Institute of Highway Safety (IIHS) tests vehicle seats and head restraints with a special dummy that has a realistic spine. The vehicle seat — with the dummy in it — is placed on a sled, which is moved to simulate a rear impact.