Low Impact Motor Vehicle Collisions And Whiplash Injury

It is clear that automobile accident insurance company claim adjusters, automobile accident insurance company defense attorneys, and defense medical/chiropractic experts believe that an individual in a vehicle involved in a collision cannot be injured if the vehicle sustains only minimum structural damage. Yet, there is no doubt that individuals involved in minimum structural damage collisions develop symptomatology consistent with whiplash type neck distortion soft tissue injuries. Practicing health care providers who examine these patients document findings that are consistent with soft tissue trauma. These include alterations of segmental motion, alterations of joint end play, postural distortions, alterations of normal tissue textures, abnormal sensitivity (pain) to local pressure, swelling, etc. In addition, more expensive diagnostic investigations often show alterations of segmental motion on stress radiography or stress MRI, permanent injuries to the alar ligaments on proton density weighted MRI, inflammatory changes consistent with soft tissue injury on thermography, abnormal neurological function with surface EMG, objectively measured reduced pain thresholds with algometry, and objective alterations of global range of spinal motion with dual inclinometers.

With adamant claims by patients that their symptoms are genuine and by doctors that their findings are genuine, there arises the cynical perspective that the patient’s prime objective is secondary gain and that of the doctor’s is greed.

The mathematical principles of collision physics are complex and unique for each accident. Yet, they can be simplified, as many of the forces involved are so small that for practical purposes they are negligible. Importantly, these principles often support the position of the patient and their doctor.

In 1687, at the age of 43, Sir Isaac Newton published the book Principia Mathematic, which is among the most influential books in the history of science. In Principia Mathematic, Newton describes the three Laws of Motion. It is Newton’s Laws of Motion that explain contemporary whiplash trauma and subsequent injury. The most important Law is his first, the Law of Inertia. Simply stated in the context of whiplash trauma, things at rest tend to remain at rest, and different parts of the same object can have different inertias.

The human body has two large parts that have their own separate inertia, the trunk and the head. These two large pieces of inertial mass (the head and the trunk) are connected by the thinner structure of the cervical spine. During a motor vehicle collision, a vehicle that is struck from behind will quickly move forward. As the vehicle moves forward, so do the passenger seats in the vehicle. As the passenger seat moves forward, so does the trunk of the passenger sitting in the seat. However, the head of the passenger in the seat does not move forward because the head has a separate inertia from the trunk. As the vehicle, the seat, and the trunk move forward from the collision, the head remains at rest, forcing the neck backwards. The result is an inertial injury to the soft tissues of the vertebral joints of the cervical spine. Importantly, the neck does not hit anything; it sustains an inertial injury, similar to that seen in shaken baby syndrome.

The type of injuries chiropractors treat that result from rear impact motor vehicle collisions are classified as “inertial acceleration injuries.” Popular terminology within our profession is “cervical acceleration / deceleration syndrome,” or CAD (Foreman and Croft). These inertial acceleration injuries to the cervical spine are proportional to the acceleration achieved by the struck vehicle. The greater the acceleration of the struck vehicle, the greater the acceleration injuries to the cervical spine structures. Importantly, sufficient vehicle acceleration to cause cervical spine inertial acceleration injuries can occur with no or minimal vehicle structural damage. This concept is adequately explained by Robbins (Journal of the Society of Automotive Engineers, 1997) and others, below. Robbins article is titled:

In agreement with above, Robbins states that injury is linked to the magnitude of the acceleration achieved by the struck vehicle. Acceleration is expressed in the units of “G” which stands for the acceleration of gravity. Falling in gravity is not a velocity (a steady speed), it is an acceleration (going faster every second). 1G = 9.81 meters/second2 (m/s2). Robbins states the pertinent mathematical formula is from the great Italian physicist, mathematician, and astronomer, Galileo (d. 1642):

a = V2/2s

a = acceleration

V = velocity of impact

S = the crush distance of the vehicle

Using Galileo’s mathematical formula, Robbins cites two examples:

Velocity (V)

12 m/s

12 m/s

Crush Distance (s)

1 meter (m)

.2 meter (m)

Acceleration (a)



Acceleration (a)

122/(2) X (1)

122/(2) X (.2)

Acceleration (a)



Acceleration (a)

72 m/s2

360 m/s2

Acceleration (a)

72 m/s2 / 9.81 m/s2

360 m/s2 / 9.81 m/s2

Acceleration (a)

7 Gs

36 Gs

Look at the numbers carefully. In the second example, for the same velocity, crushing the vehicle 80% less (1 meter versus .2 meters) resulted in significant more vehicle acceleration (5 times more [7 Gs v. 36 Gs]). The results show that the greater the crush damage distance of the vehicle, the less the G force received by the occupant. Or, the smaller the crush damage distance of the vehicle, the greater the G force received by the occupant, which is associated with greater acceleration inertial injury.

The use of stiff motor vehicle bodies and chassis, when subjected to relatively severe impacts, may result in little or no damage to the vehicle body or bumper, yet the occupants are subjected to high G force, resulting in whiplash injury. Robbins states:

“… crush damage does not relate to the expected occupant injury, i.e., the more vehicle damage, the more the chance that the occupant is injured, is not a conclusion that can be made. In fact, it is more likely the opposite.”

Studies clearly indicate that motor vehicles can withstand a reasonably high-speed impact with little or no accompanying vehicle damage (Navin). Unfortunately, when vehicle damage energy is reduced, the energy is transferred into acceleration, causing patient injury. Current bumper standards have the effect of reducing property damage while subjecting the occupants to a more acceleration and more violent ride, increasing the probability of occupant injury (Navin, Smith).

Published experts in motor vehicle collisions have completed experiments (Navin, Emori) or made observations which conclude that the degree of patient/passenger injury from automobile collisions is not related to the size, speed, or magnitude of damage of the involved vehicles. Navin and Romilly state (1989):

“…experimental results indicate that some vehicles can withstand a reasonable high speed impact without significant structural damage. The resulting occupant motions are marked by a lag interval, followed by a potentially dangerous acceleration up to speeds greater that of the vehicle.

A review of accident reports indicates that a significant percentage occur with little or no accompanying vehicle damage.

As the vehicle becomes stiffer, the vehicle damage costs are reduced as less permanent deformation takes place. However, the occupant experiences a more violent ride which increases the potential for injury.

…the average acceleration experienced by the occupant in the elastic [no damage] vehicle would be approximately twice that of the plastic [structurally damaged] vehicle. This theory implies that vehicles which do not sustain damage in low speed impacts can produce correspondingly higher dynamic loadings on their occupants than those which plastically deform under the same or more severe impact conditions.”

Emori and Horiguchi state (1990):

“…neck extension became almost 60° which is the potential danger limit of whiplash, at collision speed as low as 2.5 km/h.”

Robbins notes (1997) that it is false reasoning and a misconception to claim that vehicle crash damage offers a correlation to the degree of occupant injury. He states:

“This false reasoning is often applied by insurance adjusters, attorneys and physicians and frequently results in costly unjustified litigation. Due to this litigation process, the injured parties often are not compensated, resulting in unjustified hardship to the party who has already been injured.”

Historically, a number of authors have made the observation that vehicle damage is not an indicator of occupant injury. In 1964, physician and whiplash expert/author Ruth Jackson, MD, wrote:

“The forces which are imposed on the cervical spines of the passengers of colliding vehicles are tremendous, and if one attempts to calculate mathematically the amount of such forces, the results are unbelievable.” “The damage to the vehicles involved in collisions is no indication of the extent of the injuries imposed on the passengers.”

“The extent of damage to the vehicles is in no way proportional to the extent of damage imposed upon the cervical spines of the passengers.”

Ian Macnab, MD, states (1982):

“The amount of damage sustained by the car bears little relationship to the force applied. To take an extreme example: If the car was stuck in concrete, the damage sustained might be very great but the occupants would not be injured because the car could not move forward, whereas, on ice, the damage to the car could be slight but the injuries sustained might be severe because of the rapid acceleration permitted.”

Carroll et. al. state (1986):

The amount of damage to the automobile bears little relationship to the force applied to the cervical spine of the occupants. The acceleration of the occupant’s head depends upon the force imparted, the moment of inertia of the struck vehicle, and the amount of collapse of force dissemination by the crumpling of the vehicle.

Author Ameis, MD, states (1986):

“Each accident must be analyzed in its own right. Auto speed and damage are not reliable parameters.”

Hirsch et. al. state (1988):

“The amount of damage to the automobile may bear little relationship to the forces applied to the cervical spine and to the injury sustained by the cervical spine.”

Smith states (1993):

“The absence or presence of vehicle damage is not a reliable indicator of injury potential in rear impacts. Based upon the principle of conservation of energy, any energy which does not go into damaging the vehicle must be converted into kinetic energy, the source of injuries.”

Nordhoff and Emori state (1996):

“Historically, insurance company claims adjusters have assumed that collision injuries correlate to the vehicle external structural damage and cost repair. … The assumption that injuries relate to the amount of external vehicle damage in all types of crashes has no scientific basis.”

“There is little correlation between neck injury and vehicle damage in the low-speed rear-end collision.”

Rene Cailliet, MD, states (2006):

“Numerous injuries result from vehicular accidents even when the impacts are not very big and there is minimal damage to both vehicles.”

“In many instances, a person experiences whiplash after a vehicle accident that has caused little significant damage to either vehicle.”

Henderson states (2006):

Collisions between motor vehicles and the occupants of those vehicles must conform to Newton’s Laws of Motion.

“Historically, the argument about injury or likelihood of injury had been the domain of the medical experts, albeit without any true scientific evidence on which to base an opinion.”

A struck vehicle will accelerate forward, with or without vehicle damage. This will cause accelerations of the occupant’s chest and head.

Crashes resulting in a change in velocity of 5.97 mph of the struck vehicle cause a 4.7 g acceleration of the occupant’s chest and an 8.3 g acceleration of the occupant’s head. The difference between the head and chest acceleration is 3.6 g. This resulted in the symptoms of strains and headaches.

Not all occupants will react in the same manner to the same change in velocity.

“It is my opinion that beyond a speed change of 5 mph, the risk of injury is high.”