Whiplash refers to an injury to the neck resulting from a rapid movement, usually associated with a motor vehicle collision (MVC). However, it can occur with a slip and fall injury, a bar room brawl, or during a sports event (like being tackled in football), among other things. For the sake of this discussion, we will stick with the classic example of a rear-end MVC.
Mechanism of injury: So what really happens during the MVC that causes injury? The answer centers around a movement of the neck which exceeds the normal tissue’s stretch limits, sometimes referred to as “the elastic barrier.” When the MVC occurs, during the first 100-200 milliseconds, the trunk supported by the back of the car seat rapidly moves forwards leaving the head unprotected in its original position resulting in a backward glide or motion of the head and neck. Next, the head (which weighs about 12-15 pounds or about 5-7 kg) drops back (HOPEFULLY) into the headrest stopping the motion, but if the head rest is too far back (>1/2 inch or just over 1 cm) or too low, then the head keeps going backwards until the tissues in the front of the neck stretch to the point of either stopping the motion or tearing (or both). Next, the highly stretched front of the neck muscles, ligaments, disks, and tendons (in a “crack the whip” like manner) propel the head forwards to the point of over stretching the tissues in the back of the neck, which similarly stops the movement &/or tears. The degree of injury depends on many things, but is notably worse in people with long, skinny necks. Several factors determine the degree of injury, including the “G-Force,” or the amount of energy produced during the impact. The greater the G-force applied to the head/neck, the greater the potential for injury. The G-force affecting the occupants inside the vehicle is related to many things: the speed of the crash, the size of the two vehicles (worse if a large automobile hits your smaller car), the angle and springiness of the seat back, the amount of energy absorbed by crushing metal vs. no damage to the vehicles (worse when there is no damage as all the energy is transfer to the occupants), whether the head was rotated or looking straight at impact, and more. The KEY to all of this is that we cannot voluntarily contract our muscles quicker than 800-1000 msec and the whiplash process is over after about 500 msec, so we can’t effectively “guard” or protect ourselves against injury even if we try by bracing ourselves before the MVC!
Type of injury: The classic injury is called a sprain (ligament tear) and strain (muscle and/or muscle tendon tear) to either or both the front of the neck and/or back of the neck. Sprains and strains come in 1st, 2nd, and 3rd degree tears, getting progressively worse as more tissue is torn.
Prognosis: The length of time to recovery or maximum improvement varies by the amount of tissue damage. A “prognosis scale,” first introduced in 1995 and validated by 2001, showed that in Type 1 injuries pain without loss of neck motion healed the quickest. Type 2 injuries where neck movement was reduced after the MVC (but no neurological findings occurred) healed next quickest. Type 3 injuries, which included BOTH motion and neurological loss, healed the slowest and had the worst long-term outcomes. Other factors enter into this, of course.
We will continue this “Whiplash 101” discussion next month…
Don't miss the next article, click here for part 2.
