Head restraints designed to protect riders in many of today's automobiles can actually make whiplash injuries more severe, according to an article published in the July 2000 issue of the Journal of the American Chiropractic Association (JACA). Studies done on low-speed, rear-impact crashes show that less than 30 percent of Americans adjust their head restraints properly to begin with, and even those who adjust them properly often end up with whiplash injuries brought on by the head restraint itself.
According to the article's author, Arthur Croft, DC, director of the Spine Research Institute of San Diego, CA, the impact of a crash will make an occupant's head rise above a restraint even one that's properly adjusted -- an effect called "ramping." Ramping is the combined result of a person gliding up the seat back and a temporary straightening of the thoracic and cervical spinal curves during the crash. The head restraint actually intensifies the injury, acting like a fulcrum as the head crashes down onto the restraint and hammers it into a lower position, according to Dr. Croft.
Another critical factor in whiplash injuries is the "backset," or the distance between a person's head and the restraint at the moment of impact. In his article, Dr. Croft concludes that if an occupant's head is more than two inches away from even a perfectly-positioned and well-anchored restraint, the restraint is useless.
According to Dr. Croft, carmakers should build a "seat back designed to absorb acceleration forces by incorporating a system that would allow a limited slow collapse of the seat back with fluid-damping characteristics" -- something that would envelop the occupant, absorbing the effects of the crash on the body. "This just about perfectly describes Volvo's new Whips seat, which is found in the new S80 model," says Dr. Croft. "Saab also has a revolutionary new seat back/head restraint design that it is incorporating into some models. We will be crash-testing some of these seats later this year at this institute."
Dr. Croft adds cautiously that although he is hopeful about the new seats, there are still problems that need to be addressed in the future. Most seats are designed for 50th percentile male body types, and don't take into account smaller or larger physiques. In addition, because a whiplash injury takes place within the first 200 milliseconds -- which means that it happens even before the head makes contact with a head restraint, well-positioned or not -- the head and neck are pushed into a physically harmful position so fast on impact that the head restraint is useless to prevent it.
Dr. Croft concludes that whiplash is not as simple as once believed. Because the neck assumes a more complex position on impact than previously thought, researchers will need to conduct more crash studies to find out not only what is actually happening physically during a whiplash injury, but also what automobile manufacturers need to incorporate into their designs to prevent whiplash in the first place.
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