Over the next several weeks, we will post a total of 10 short articles about whiplash injuries from auto collisions, a poorly understood but all too common injury. Our firm handles many such cases and is committed to informing you so you can protect yourself and your family.
4.) The Physics and Mechanism of the Whiplash Injury
In a rear end collision, the body of the person struck is instantaneously accelerated forward by the motion of his seat back. The head lags behind because of its inertia. The top of the neck initially flexes forward due to the inertia of the head. Then the head flies backward and down as it is pulled by the neck violently extending backward.
The vertebral bones of the neck are stacked in a flexible column. They are alternatively crunched together in the front and then in the back by this motion. The motion stretches and tears the ligaments and muscles holding them in place. In the upper neck, due to the initial inertia of the head, there is a double alternating motion between the vertebral bones. This is why victims of whiplash so often suffer upper neck pain, instability and headaches. The jaw often flies open causing injury to jaw joints and inner ears.
At the second stage of the collision the head rebounds from its rearward position and flies forward, rotating downward as the body strikes and wraps around the seat belt. There is almost never an air bag inflation in rear end collisions to restrain any of this motion. The rear end collision is one occasion where seatbelts may actually enhance the amount of injury due to whiplash.
All of this takes place in a few tenths of a second. Most people don’t realize what has happened. Appreciating the violence done to the neck requires extreme slow motion photography. Needless to say, the countless nerves, vessels, ligaments, bones, and muscles in the human neck are not designed to sustain such trauma without injury.
Physicists describe the forces acting on the structures of the spine during whiplash as axial compression, shear, bending moments, pressure transients, torque or rotation. Most of this boils down to relative motion of the vertebral bones and the resulting damage to attached tissues.
Physics also comes into play regarding the acceleration forces that act on the car, torso and head in rear end collisions. These forces are often referred to in units of 1 gravity or “G” equaling the strength of gravity on Earth. For example, a force of 2 “G’s” applied to the car results in 5 G’s to the torso and 7 G’s to the head of the victim. Low speed does not equal no injury.