Whiplash injuries are not generally recognized as the serious, disabling injuries that they can be. Many times, the term “litigation neurosis’ is used to describe those who complain of persistent symptoms in what seems to be a minor accident. Many studies have been done to determine whether or not “litigation neurosis” (conscious or unconscious exaggeration or fabrication of complaints) plays a significant role in cervical acceleration/deceleration (CAD) cases (1,2,3,4,5,6,7) . These studies have found that litigation does play a significant role in the outcome of CAD traumas. In fact, recent research indicates that there is much more impact on the victim’s life for a much longer span of time than had been believed previously.
First, we must dispel the commonly held belief which equates the amount of damage to the vehicle with the degree of injury to its occupants. Actually, it is often the collision that causes minor damage to the vehicle that causes a great deal of injury to its occupants. To understand why this is so, we must understand the difference between elastic and plastic deformation of the vehicle.
Elastic deformation involves a momentary deformation of the steel, followed by a spring-like reaction back toward its original shape (10) . The energy of the collision is not absorbed, but acts in a way similar to that of a cue ball when it strikes another billiard ball. The cue ball (in this case the vehicle which strikes the other) stops. The other ball (the vehicle which is rear-ended) is rapidly accelerated. It is precisely this rapid acceleration that is the mechanism of injury.
Plastic deformation, on the other hand, is permanent. The energy of the collision is absorbed by the steel. It collapses in on itself and stays there. Plastic deformation is what happens when you smash two empty milk cartons together. The occupants of the car (and the auto body shop) want a plastic collision. The best cars “accordion” when hit, allowing the car to absorb the force (9). When the car does not absorb the force, its occupants do (9)
For the sake of simplicity let’s assume that the vehicle is an automobile with one occupant: a fifty year old female. She is stopped at a red light when another car hits her from behind at eight miles per hour (the speed which experimenters used to calculate the “G-force” of a rear-end collision (10)). Her foot is knocked off the brake (as often happens) and her car is rapidly accelerated forward.
First, she is thrown backward. If her head-restraint is properly adjusted or if she has a car seat which incorporates the head-restraint in its design (high-backed seat), her head will strike it. This limits hyperextension. Often, however, the head-restraint is left in its lowest position. This causes it to act as a fulcrum, around which even greater injury occurs. Even if the~ head-restraint if adjusted properly, if the driver is leaning forward at the moment of impact (a common habit), the effect of the headrest will be decreased. (11))
Ramping is another phenomenon which must be taken into account. This is an upward motion toward the top of the seat which happens involuntarily upon impact (12) . If the driver is tall, ramping may negate the effect of the headrest altogether, since her head will be thrown over the top of the seat.
Once she has been pushed back into the seat, her direction reverses. Now, her chest and shoulders begin to move forward. (At this point, her head is still pressed backward.) Suddenly, her head whips forward. In an eight mile per hour collision, this force has been measured to be five (5) times the force of gravity (10)! The shoulder harness, while saving her from serious head injuries, actually increases the likelihood of neck injuries by stopping the body - thereby increasing the relative speed of her head. (All of this takes place in approximately three tenths of a second. (10))
The force of impact goes beyond the tensile strength of the muscles and ligaments of the neck and back. These tissues are actually torn. Nerves can also be injured. Traction injuries of the nerve roots are common (especially when the victims head was turned at the moment of impact). Compression of nerve roots often follows disc injury. (The ~wol1en disc traps the soft nerve between it and the bone.) An inflammatory process ensues in all of the soft tissues. If the force is great enough, compression fractures of the bones can occur.
Concussion (even without the head striking anything) is common. Damage to the temporomandibular joint is another injury common to these accidents.
The degree of injury depends upon several factors:
1. Was the vehicle stopped? If so, did the driver have her foot on the brake? Remember, rapid acceleration is the mechanism of injury. If the driver is stopped and manages to keep her foot on the brake, injury will be less than it would be if the car were able to rapidly accelerate (10) . (One could argue that, while the acceleration forces would be reduced, the deceleration forces would be increased, thus increasing injury during that phase of the collision.)
2. Did the headrest properly support her neck? If she is very tall or did not have the headrest adjusted properly, “ramping’ may have negated the usefulness of that ordinarily useful device.
3. Did she see the accident coming? Bracing in anticipation of a collision helps to protect the accident victim. The tensed shoulder and neck muscles decrease the acceleration of the head, thus somewhat limiting the extent of the injuries (10)
4. What is the driver’s age? Our driver is fifty years old. Her reaction time ~is a bit slower than it used to be. Therefore, she may not have been able to brace herself for the injury. At age fifty, it is common to have some wear and tear (osteoarthritis) of the spinal structures. This could make her susceptible to extensive injury in an accident in which a twenty year old might suffer little or no ill
effects (12).
5. What is the person’s sex? Our driver is a female. Females involved in this type of accident generally report injury more frequently than males. In part, this may be due to the fact that they do not feel compelled to “take it like a man”. There is also an anatomical reason for this increased risk. A woman’s musculature is, on the average, not as thick and, consequently, not as strong as that of a man. Therefore, a woman has less of an ability to brace herself (7,13,14).
6. What are the relative masses of the two vehicles? Obviously, a bus will create more force than a “Cooper Mini”. Actually, a streetcar moving at 3 miles per hour will deliver the same amount of force as an compact sized automobile traveling at 40 (18) 1
7. Did she have her seatbelt fastened? As said before, seatbelts save lives, but they increase the “whiplash” force (8)
8. How rigid was the seat? A seat made of more “springy” material can act like a diving board and increase the force of the rebound the victim experiences after she is thrown back against it (10,15)
9. Was she leaning forward when she was hit? Many drivers have the habit of leaning toward the steering wheel when they drive. As stated before, this diminishes the bracing effect of the head restraint (16)
10. Did she have any prior conditions? Sometimes an accident victim will deny a prior condition on the mistaken belief that it will “hurt my case”. The truth is that a prior condition almost always increases the severity of the injury and may contribute to predisposing the victim to injury in an accident where, otherwise, she may have escaped unscathed (10)
11. What were the road conditions? All other factors being equal, a collision on a wet road will cause more injury than a collision on a dry road. This is because the loss of traction will cause more rapid acceleration (8)
A recent study shows that 86% of those who had reported acceleration/deceleration injuries were still symptomatic ten years after the accident (17) Of these, l3% complained of serious disruption of their lives. Clearly, these injuries are serious and can cause significant disabilities.
References:
l)Norris SR. Watt I: The prognosis of neck injuries resulting from rear-end vehicle collisions. J Bone Joint Surg 56A(8) :1675-1682,1974
2)MacNab I:Acceleration injuries of the cervical spine. J Bone Joint Surg 46A(8) : 1797-1799,1954
3)Schutt CH, OohanFC: Neck injury of women in auto accidents JAr’L 206 (12) :2689-2692,1968
4)Watkinson A, Gargan MG, Bannister GC: Prognostic factors in soft tissue injuries of the cervical spine. Injury: Brit J Accid Surg 22 (4) :307-309,1991
5)Bohrer SP, Cherr YM, Sayers DG: Cervical spine flexion patterns. Skeletal Radiol 19:521-525,1990
6)Maimarjs C, Barnes MR. Allen MJ: ‘Whiplash injuries’ of the neck: a retrospective study. Injury: Brit J Accid Surg 19(5): 393-396,1988
7)Hohl M: Soft tissue injuries of the neck in automobile accidents: Factors influencing prognosis J Bone Joint Surg 56A(8) :1675-1682,1974
8)Foreman SR. Croft AC: Whiplash Inluries: The Cervical Acce1eratjon/Deceleration Syndrome. Baltimore, Williams & Wilkins, 1988, p62
9)lbid, p67
10)Severy DM,Mathewson JH,Bectol CP: Controlled automobile rear-end collisions, an investigation of related engineering and mechanical phenomenon. Can Services Med J 11:727,1955
l1)Foreman SI-I, Croft AC: Idem, p63
l2)Ommaya A,Backaitj~j S,Fan W, Partyka S: Automotive neck injuries. Ninth International Technical Conference on Experimental Safety Vehicles,Us Dept of Trans,Nat Highway Traffic Safety Admin, Kyoto, Japan,Novl—4, 1982,pp274-278
13)Pearce JMS: Whiplash injury: a reappraisal J Neurol Neurosurgery Psychiatry 52:1329-1331,1989
14)Balla JI: the late whiplash syndrome. Aust NZ J Surg 50(6) :610-614,1980
15)Strother CE,James MB: Evaluation of seat back strength and seat belt effectiveness in rear-end impacts. In: Proceedings, 31st StrapQ Car Crash Conference SAE 8722l41Detroit,MI,Society Qf Automotive Engineers, 1987
16)Mertz HJ Jr, Patrick LM: Investigation of the kinematics and kinetics of whiplash. In: Proceedings, 11th Strapp Car Crash Conference SAE 67O919,Detroit,lvJI,gociety of Automotive, Engineers, 1967
l7)Gargan FF,Bannister GC: Long-term prognosis of soft-tissue injuries of the neck. J Bone Joint Surg 72B(5) :901-903
18)McNab I: Acceleration extension injuries of the cervical spine. In Rothman RH, Simeone FA (eds): The Spine, ed 2. Philadelphia, WB Saunders,1982, vol2 ,p654
