Whiplash and brain injury educational materials

Whiplash Injury

Educate juries about the anatomy of auto injuries with our popular Auto Injuries PowerPoint

 

The Latest on Whiplash: The World Congress on Whiplash-Associated Disorders

The World Congress on Whiplash-Associated Disorders was held in Vancouver, British Columbia, February 7-11 of this year. The following is an review of two of the studies presented.

Predicting Symptoms From Low Speed Collisions

Everyone involved with the whiplash problem wishes for some predictor of who is likely to be injured from a rear-end collision. One group of researchers1 attempted just that, by performing rear end collisions with 41 test subjects at 2.5 and 5 mph. The researchers collected acceleration data during the tests and calculated 30 different acceleration parameters resulting from the staged collisions.

All test participants were carefully screened and removed from the test if they had any history and/or risk of cervical spine injury; all potential subjects were given MRIs to aid the screening process. Furthermore, all subjects were healthy, symptom-free adults between 20 and 40 years of age. Of the 75 crashes that were completed, 23 resulted in symptoms: nine at the 2.5-mph level, and 13 at the 5-mph level. All of the symptoms were considered minor and lasted no longer than five days after the test collision. Considering the healthy test group, it’s somewhat surprising that 31% of the 75 test subjects reported symptoms in these very low speed collisions.

After carefully analyzing the calculated accelerations experienced by the test subjects, the authors found that there is no simple model for predicting whiplash symptoms. In fact, the most reliable method the researchers found consisted of 16 different factors, and even then, the model was only 80% accurate.

Although the authors conclude that this model has very little clinical usefulness (due to its complexity), the study does illuminate some controversial aspects of whiplash trauma.
First, the physics of the collision may not be as important as occupant factors. "Given the limited ability of the kinematics-based model to reliably predict symptoms, it can be assumed that other variables, such as variations in the injury tolerance of biological tissue or differences in pain perception, also play a role in injury causation and symptom production."

Second, this study demonstrates that making assumptions about the likelihood of injury from a particular collision (as often happens in court cases by insurance adjusters or accident reconstructionists) is risky.

The authors specifically refer to the study by Allen et al2 (popular with defense counsel) that claimed that the accelerations experienced during whiplash trauma were no different than those motions experienced in daily life, such as "plopping down in a chair." Allen et al looked only at single peak accelerations. Since a complex model of 16 different variables is unable to perfectly predict symptoms, then obviously a model consisting of just one variable cannot. Furthermore, the Allen et al2 study examined only horizontal head acceleration, and this particular variable did not even show enough significance to be included in the 16 variable model!

The authors state,

"...the analysis showed that no one parameter was sufficiently strong to successfully predict symptoms...Even with detailed knowledge of the global and relative head and neck kinematics, the best model correctly predicted only about half of the tests which resulted in symptoms. These results indicate that the practice of predicting injury from a single peak kinematic response variable can lead to erroneous conclusions."1 [Emphasis added.]

In short, it is difficult to predict whether or not an occupant in a rear end collision will be injured, even when all the accelerations and motions of the occupant are measured in a laboratory setting. To predict the risk of injury without this information, or from photographs of the apparently undamaged car, is impossible.

Anticipating the Collision and the Risk of Injury

Numerous researchers have suggested that an unaware occupant is at a higher risk of injury during a rear end collision, because the person will not have the opportunity to tense the musculature of the neck and protect it from injury. There is little engineering data on this issue. Mertz and Patrick3 in 1967 found that a tensed test subject experienced reduced head accelerations than an occupant who did not tense before the collision.

A paper by Kumar et al4 presented at the World Congress dealt specifically with this issue for the first time. These researchers subjected fourteen test subjects to four different intensities of low velocity impacts (.5, .9, 1.1, and 1.4 g). The different forces were randomly applied, so the occupant was unaware of how much impact was going to be experienced. During half the tests, the test subject was told to prepare for an impact, and in the other half, the test subject was unaware of the impending impact.

The graph below illustrates the differences in aware versus unaware in men and women. A number of interesting trends can be seen.

jfj

First, women appear to experience higher accelerations than do men in the same types of collisions. This has been suggested by other researchers, and may be one reason why women are more likely to be injured in a collision.

Secondly, having awareness of the impending collision does seem to have a protective effect, as the accelerations in the expected impacts are significantly lower. The authors found that, in men, anticipating the impact can reduce peak head accelerations by 27% to 37%; in women, anticipation of impact can reduce peak head accelerations by 29% to 34%. "Since its influence is in reducing the head-neck motion and acceleration (by approximately 30%), it is suggested that awareness of impending impact will reduce the potential of a whiplash injury in rear end collisions."

One possible limitation of this study should be noted. The accelerations experienced by these subjects were very low—a maximum of 1.4 g. In contrast, Szabo and Welcher5 found that cars in collisions of just 5 mph can experience peak accelerations of 3 g to 4 g, and collisions of 10 mph can result in peak accelerations of 5 g to 6 g. Whether the results of the current study apply to higher force collisions will require further study.

  1. Siegmund GP, Brault JR, Wheeler JB. The relationship between clinical and kinematic responses from human subject testing in rear-end automobile collisions. Compendium of papers presented at the Traffic Safety and Auto Engineering Stream, World Congress on Whiplash-Associated Disorders 1999;182-207.
  2. Allen ME, Weir-Jones I, Motiuk DR, et al. Acceleration perturbations of daily living: a comparison to 'whiplash.' Spine 1994;19:1285-1290.
  3. Mertz HJ, Patrick LM. Investigation of the kinematics and kinetics of whiplash. 1967; SAE 670919.
  4. Kumar S, Narayan Y, Amell T. Role of awareness in head-neck acceleration in low velocity rearend impacts. Compendium of papers presented at the Traffic Safety and Auto Engineering Stream, World Congress on Whiplash-Associated Disorders 1999;276-296.
  5. Szabo TJ, Welcher J. Dynamics of low speed crash tests with energy absorbing bumpers. 1992;SAE 921573.

 

Please note that this article is copyrighted and may not be reproduced without permission. To include our articles and videos on your website, check out our chiropractic marketing.