Ever wondered why someone is hurt worse in a car wreck than someone in a similar-type wreck? It’s a good question, and one that has been extensively researched, which shows a number of different variables contribute to acute (short-term) injury risk in a collision.
What follows is a summary of this research. These test results have been published, presented at scientific conferences, and subjected to peer review. The following risk factors have been identified, and there are likely others:
Gender:
John Dolinis, Risk factors for ‘whiplash’ in drivers: a cohort study of rear-end traffic crashes 28(3) Injury 173, 177 (1997).
In an epidemiological study designed to identify vehicle and occupant factors associated with “whiplash” in drivers of passenger cars involved in rear-end collisions, researchers found the odds of injury for women was about twice that of men after adjusting for the influence of other factors.
Vector of Collision:
Neck injuries were found to be more likely among drivers of directly rear-struck cars, versus those struck in a rear corner, and in more severe crashes.
Mason Hohl, Soft tissue injuries of the neck 109 Clinical Orthopaedics and Related Research 42 (June 1975).
Rear-end impacts cause hyperextension of the neck that is only stopped when the head strikes the upper dorsal spine indicating neck movement well in excess of the range permitted by the anatomical structures.
G.T. Deans, J.N. Magalliard, Malcolm Kerr & W.H. Rutherford, Neck sprain – a major cause of disability following car accidents 18 Injury 10, 11 (1987).
Rear impacts cause neck pain twice as much as frontal collisions.
Per-Olof Bylund & Ulf Bjornstig, Sick Leave and Disability Pension Among Passenger Car Occupants Injured in Urban Traffic 23(9) Spine 1023, 1027 (1998).
Rear end collisions are the most common crash mechanism resulting in the highest sickness benefit cost, and give rise to the majority of disability pension cases.
Matthias Sturzenegger, Giuseppe DiStefano, Bogdan P. Radanov & Ayesha Schnidrg, Presenting symptoms and signs after whiplash injury: the influence of accident mechanisms 44 Neurology 688, 692 (April 1994).
This study was performed to assess the relationships between the initial clinical findings and the features of a whiplash collision.
Local physicians referred the researchers 137 patients who had recently been subjected to whiplash trauma. The patients were examined, which included an interview concerning the immediate post-traumatic and still present symptoms; features of the collision; a physical and detailed neurologic examination; and cervical spine x-rays.
Researchers analyzed several features of the collision, and found three features to have a significant influence on manifestation, severity, and multiplicity of initial symptoms.
One of these features was rear-end collisions led to significantly higher frequency of injuries or multiple symptoms.
Lotta Jakobsson, Bjorn Lundell, Hans Norin & Irene Isaksson-Hellman, WHIPS – Volvo’s whiplash protection study 32 Accident Analysis and Prevention 307, 310 (2000).
Rear-end impacts account for the highest neck injury risk, and are by far the most common injury type in rear-end impacts.
Vehicle Stiffness:
Vehicle bumper stiffness (force-deflection properties) and elasticity (the ability to return energy stored in the bumper system by the collision) determine the shape, duration, and magnitude of the collision pulse.
Stiff bumper systems produce shorter duration collisions and higher peak accelerations than compliant bumper systems, and elastic bumper systems produce collisions with a higher speed change than plastic bumper systems.
Since bumper system design influences both the vehicle acceleration and speed change during a collision, epidemiological data suggest that bumper system design influences both the severity of duration of whiplash symptoms.
Part of the whiplash injury risk can be mitigated with bumpers designed to attenuate the collision pulse.
Lotta Jakobsson, Bjorn Lundell, Hans Norin & Irene Isaksson-Hellman, WHIPS – Volvo’s whiplash protection study 32 Accident Analysis and Prevention 307, 310 (2000).
If a stiff vehicle structure is involved, a higher neck injury risk is indicated. The conclusion can be drawn it is important to focus on measures to reduce the acceleration of the car … in order to reduce the acceleration of the occupants.
Vehicle Mass:
John Dolinis, Risk factors for ‘whiplash’ in drivers: a cohort study of rear-end traffic crashes 28(3) Injury 173, 177 (1997).
In an epidemiological study designed to identify vehicle and occupant factors associated with “whiplash” in drivers of passenger cars involved in rear-end collisions, researchers found the ratio of the striking masses was a better and statistically significant predictor of injury risk. The risk was greatest where the striking car was in a heavier weight class than the driver’s car. This finding was consistent with other studies that found that injury risks increase as a power function of the mass ratio.
The relative risk of “whiplash” occurrence in drivers of light vehicles was 1.43 times that for drivers of heavy vehicles, and there was a positive association between the weight of the striking vehicle relative to the weight of the struck vehicle and the risk of “whiplash” injury to the driver of the struck vehicle.
Headrest Position:
David C. Viano & Martin F. Gargan, Headrest position during normal driving: implication to neck injury risk in rear crashes 28(6) Accident, Analysis & Prevention 665, 672-73 (1996).
Drivers are more at risk for whiplash injuries when the headrest is in the down position. Nine out of ten drivers in a sample of nearly 2,000 had headrests in this position during normal driving than in the upright position, which provides the most protection against whiplash injuries in a rear crash. This indicated that the majority are at risks varying from 1.6 to 6.0 times greater than the most favorable condition during normal driving.
Matthias Sturzenegger, Giuseppe DiStefano, Bogdan P. Radanov & Ayesha Schnidrg, Presenting symptoms and signs after whiplash injury: the influence of accident mechanisms 44 Neurology 688, 692 (April 1994).
This study was performed to assess the relationships between the initial clinical findings and the features of a whiplash collision.
Local physicians referred the researchers 137 patients who had recently been subjected to whiplash trauma. The patients were examined, which included an interview concerning the immediate post-traumatic and still present symptoms; features of the collision; a physical and detailed neurologic examination; and cervical spine x-rays.
Researchers analyzed several features of the collision, and found three features to have a significant influence on manifestation, severity, and multiplicity of initial symptoms.
One finding was proper use of headrest can reduce the incidence of neck pain in a rear end collision by 24%, but approximately 75% of adjustable restraints are left in the down position.
Awareness of Impact:
G. Anthony Ryan, GW Taylor, VM Moore & John Dolinis, Neck strains in car occupants: injury status after 6 months and crash-related factors 25 Injury 533, 534 (1994).
This study sought to identify factors associated with the initial severity of the injury and with the duration of symptoms.
Participants who were unaware of the impending collision were 15 times more likely to have a persisting condition than those who were aware.
The researchers concluded this finding provided evidence of a distinction between individuals who have and have not recovered from their symptoms 6 months after the collision.
John Dolinis, Risk factors for ‘whiplash’ in drivers: a cohort study of rear-end traffic crashes 28(3) Injury 173, 176 (1997).
As the degree of driver awareness increases, as measured by the number of reported sources of forewarning, so too does the protection against “whiplash” injury.
Matthias Sturzenegger, Giuseppe DiStefano, Bogdan P. Radanov & Ayesha Schnidrg, Presenting symptoms and signs after whiplash injury: the influence of accident mechanisms 44 Neurology 688, 692 (April 1994).
This study was performed to assess the relationships between the initial clinical findings and the features of a whiplash collision.
Local physicians referred the researchers 137 patients who had recently been subjected to whiplash trauma. The patients were examined, which included an interview concerning the immediate post-traumatic and still present symptoms; features of the collision; a physical and detailed neurologic examination; and cervical spine x-rays.
Researchers analyzed several features of the collision, and found three features to have a significant influence on manifestation, severity, and multiplicity of initial symptoms.
One of these features was the state of preparedness, which proved to be the first significant factor with respect to initial findings. Patients prepared for the impact had a significantly lower frequency of multiple symptoms and lower intensity of headache.
Since multiple symptoms as well as intensity of headache were associated with a less favorable prognosis and a more severe injury, prepared occupants seemed to sustained less musculoligamental strain.
Reflexive tension of the neck and shoulder muscles or pushing the head against the restraint might be protective preventive measures.
The authors noted a 1955 study (DM Severy, JH Mathewson & CO Bechtol, Controlled automobile rear-end collisions, an investigation of related engineering and medical phenomena 11 Can. Serv. Med. J. 727 (1955)) found in their sophisticated experiments with controlled low-speed rear-end collisions in dummy and human subjects, noted a pronounced reduction in acceleration forces to the head in the forewarned human subject and concluded that defensive action taken by a motorist when forewarned of an imminent collision significantly influenced the pattern of whiplash injury.
Head Position at Impact:
Matthias Sturzenegger, Giuseppe DiStefano, Bogdan P. Radanov & Ayesha Schnidrg, Presenting symptoms and signs after whiplash injury: the influence of accident mechanisms 44 Neurology 688, 691 (April 1994).
This study was performed to assess the relationships between the initial clinical findings and the features of a whiplash collision.
Local physicians referred the researchers 137 patients who had recently been subjected to whiplash trauma. The patients were examined, which included an interview concerning the immediate post-traumatic and still present symptoms; features of the collision; a physical and detailed neurologic examination; and cervical spine x-rays.
Researchers analyzed several features of the collision, and found three features to have a significant influence on manifestation, severity, and multiplicity of initial symptoms.
One of these features was rotated or inclined head position, which was the only accident feature related to injury severity, which is not surprising considering that the physiologically permitted range of extension is much smaller and reduced by approximately 50% when the neck is rotated; this finding is consistent with other studies showing anterior longitudinal ligament ruptures when the head is rotated before an extension strain is applied to the neck.
Koshiro Ono, Koji Kaneoka, Adam Wittek & Janusz Kajzer, Cervical injury mechanism based on the analysis of human cervical vertebral motion and head-neck-torso kinematics during low speed rear impacts SAE Technical Paper No. 973340 (November 12, 1997).
This experimental study used 12 healthy male participants with no degenerative changes in their spines, and were subjected to sled tests designed to simulate actual real-life rear-end impacts at low speeds (5.5 mph).
Accelerometers were placed on the participants’ heads, and cineradiography (DMX) was used to record the impacts.
Researchers found the initial state of neck position markedly affects the impact responses of the head and neck. Namely, the in the state of flexion … the lower cervical vertebral segments are affected by the effect of torso ramping-up motion, resulting in a greater difference in relative motions (S-shape formation). Considering this phenomenon and the facet joint injury mechanism, it can be deduced that the upward travel of the rotation center, and the amount of rotation of C5 vertebral segment, increased in the state of flexion, which facilitates the incidence of neck injury.
Bogdan P. Radanov, Matthias Sturzenegger & Giuseppe Di Stefano, Long-term outcome after whiplash injury: a 2-year follow up considering features of injury mechanism and somatic, radiologic, and psychosocial findings 74(5) Medicine 281 (1995).
This study was designed to assess the significance of injury mechanisms and of early somatic, radiologic, and psychosocial variables on outcome assessed 2 years after trauma in whiplash patients.
The sample size included 117 patients injured in motor vehicle collisions, which were all covered by insurance. Each patient was interviewed; received a complete neurologic and physical examination; received cervical spine x-rays; completed questionnaires consisting of self-ratings of initial neck pain and headache intensity; completed a personal and family history, and completed formal psychological and cognitive tests.
Out of many findings, the researchers noted patients who remained symptomatic in the long term reported significantly more rotated or inclined head position at the time of impact.
The researchers concluded these head positions make the cervical spine more susceptible to damage due to the biomechanical forces of acceleration and translation, which supports the role of the head position at impact in determining long-term outcome.
Age:
Urs Maag, Claire Laberge-Nadeau & Xiang-Tong Tao, Neck sprains in car crashes: incidence, associations, length of compensation and costs to the insurer 37th Annual Proceedings of the Association for the Advancement of Automotive Medicine 15, 16-23 (November 4-6, 1993 San Antonio, Texas).
After analyzing 4,328 claims made in 1987 for the Province of Quebec of insureds who filed insurance claims as a result of sustaining at least a neck injury in a motor vehicle collision in a study designed to measure the nature of neck injury, severity, duration of insurance compensation, and direct costs, researchers found that older age groups were injured worse than younger age groups as measured by the amount of compensation rendered by the Canadian provincial car insurance board.
Use of Seat Belts:
Abrasions at the site of belt contact is associated with significant internal injuries in approximately 30% of cases, wherein chance fractures and their ligamentous equivalents are more common than solid organ injuries from the use of restraints.
G.T. Deans, J.N. Magalliard, Malcolm Kerr & W.H. Rutherford, Neck sprain – a major cause of disability following car accidents 18 Injury 10, 12 (1987).
More neck sprains found on belted occupants than unbelted occupants.
Matthias Sturzenegger, Giuseppe DiStefano, Bogdan P. Radanov & Ayesha Schnidrg, Presenting symptoms and signs after whiplash injury: the influence of accident mechanisms 44 Neurology 688, 691 (April 1994).
This study was performed to assess the relationships between the initial clinical findings and the features of a whiplash collision.
Local physicians referred the researchers 137 patients who had recently been subjected to whiplash trauma. The patients were examined, which included an interview concerning the immediate post-traumatic and still present symptoms; features of the collision; a physical and detailed neurologic examination; and cervical spine x-rays.
Researchers analyzed several features of the collision, and found three features to have a significant influence on manifestation, severity, and multiplicity of initial symptoms.
One finding of this study was belted occupants sustain significantly more neck pain than unbelted occupants irrespective of the direction of impact. By preventing forward movement of the trunk, safety belts aggravate cervical injuries in rear end collisions.
Speed of Impact:
Koshiro Ono, Koji Kaneoka, Adam Wittek & Janusz Kajzer, Cervical injury mechanism based on the analysis of human cervical vertebral motion and head-neck-torso kinematics during low speed rear impacts SAE Technical Paper No. 973340 (November 12, 1997).
Intervertebral articular injuries may be caused in rear impact collisions where the striking vehicle is traveling less than 5 miles per hour.
Rebound capability of the seatback:
J.Y. Foret-Bruno, F. Dauvilliers, C. Tarriere & P. Mack, Influence of the seat and head rest stiffness on the risk of cervical injuries in rear impact 13th International Technical Conference on Experimental Safety Vehicles 968, 973 (November 4-7, 1991).
Researchers found that the elastic rebound of the seatback’s backward tilt increased the neck load given the same impact speed. They concluded that before seat back breakage occurs, the elastic rebounds be as weak as possible in order to limit the risk of injuries.
Change in velocity:
In an experimental study subjecting 42 participants to 2.5 mph and 5 mph rear-end collisions, researchers found the collisions produced acute objective clinical deficits in men and women, such as decreased range of motion in the cervical spine. These deficits occurred in participants with and without symptoms, which may be a function of an individual’s tolerance for, or perception of, pain. Increasing the speed range of impacts is not a viable option given the potential harm associated with exposing human participants to greater impact severity.
Occupants of the struck vehicle in a rear-end collision will eventually experience whole-body changes in velocity equal to the change in velocity of the vehicle itself, and it is conceivable that the upper limit on the change of velocity between head and torso could be double the struck vehicle’s change in velocity.
With so many different variables, it is impossible to determine an injury threshold whereby nobody can be hurt because the permutations of these different risk factors could be in the thousands or tens of thousands. It is difficult to deny the more of these risk factors one is subjected to at the time of a collision, the more likely they are to be hurt, i.e., Murphy’s law.
