Whiplash

Each year over one million people in the United States sustain whiplash injury.  About 25 percent result in long term chronic disorders although some literature suggests that 43 percent of patients will suffer long-term symptoms.  One study reported that after six months, 38 percent of patients still reported daily or constant headaches, neck pain, or neck stiffness.  Symptoms may last for months or even years and for some, it can last a life time, never making a complete recovery.  It can be especially troublesome for women who don't have as much muscle mass in the neck as men.

Whiplash injuries can range from mild muscle strain to even death.  It is believed that most people on TWA Flight 800 were killed instantly by whiplash -- not in the fireball or crash.  In many cases, symptoms don't occur until hours after the accident.  Associated symptoms include headaches, low back pain, neck pain, nausea, decreased range of motion, tingling in the arms and legs, dizziness, sleep disturbances, visual symptoms including vertigo, post-concussion syndrome, post-traumatic stress disorder, as well as carpal tunnel syndrome, fibromyalgia and travel anxiety.  Neck pain, which accompanies all whiplash injuries, reminds the victim of the accident continually and interferes with common daily activities.

Understanding the 'whiplash injury' event has been a slow process due to the nature of the injuries.  The injury mechanism, or the biomechanics of the 'whiplash' event are not fully understood.  Crash test dummies have not been able to provide adequate whiplash injury criteria and human volunteers have often been considered the most reliable source of obtaining data.  Early whiplash tests involved monkeys and even recently, cadavers have been used to understand the mechanics of the injury.  Accident reconstruction experts measure the injurious forces generated in a car accident with arrays of accelerometers attached to a crash test volunteer.  Occupant G forces are compared to vehicle velocity or more specifically the change in velocity of the impact vehicle, or Delta V.

Recent studies at Chalmers University of Technology in Sweden suggest that rapid changes in the spinal column pressure cause damage to the nerves.  Rapid change in the spinal fluid result in pressure damage to nerve fibers because the forces that occur during a rear impact happen too fast to allow normal fluid exchange.  This research indicates that the speed at which the motion occurs is more critical compared to the extent of the neck motion.  Some studies show that the range of motion is equally important.

Head angular acceleration and resultant linear head acceleration are considered key injury predictors.  The head angular acceleration refers to the speed of the rotation of the head around its axis (see photos above), and the resultant linear head acceleration refers to the overall speed the head travels on a linear or horizontal plane.  Reducing either or both of these factors would result in reducing the severity and duration of whiplash injuries.