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Injury FAQs at Spine and Laser Center

Q: Is there a threshold below which injuries cannot occur?

Most motorists have experienced minor collisions and impacts in the course of their driving careers. These usually do not result in injury. Many motorists are involved in higher speed crashes in which significant damage to their vehicle results, and still are spared an injury. On the other hand, injuries are also known to occur in lower speed crashes in which the vehicle’s damage is minimal. On the face of it, this would seem to defy logic. Perhaps even more perplexing is the all too common example of a horrific crash in which one of the vehicle’s occupants is killed, while another walks away without so much as a scratch.

These examples make it obvious that injury risk is dependent on many factors, and these factors are not necessarily shared by all vehicle occupants equally. It follows that in lower speed crashes, a vehicle’s occupants may not share injury risks equally. Crash parameters, or crash metrics, include the vehicle’s velocity, its change in velocity (delta V) as a result of the collision, and the acceleration forces resulting from the collision. From this, it is possible to roughly gauge the effects on the occupants. However, it is known that a number of other factors can increase or mitigate the risk for injury. For example, in the classic whiplash trauma, females are at twice the risk as males. Persons who are caught unaware in a crash are at greater risk of injury than those who are able to brace for the impact. Having the head turned at the point of impact will also increase the risk of injury, as will a history of neck injury or neck pain. And there are dozens of other factors which can influence the risk for injury. Thus, in order to assess the true risk in such a crash exposure, it is helpful to know not only the crash parameters, but the human risk factors as well. In fact, the latter might very well provide a better prediction of injury than the former in low speed crashes.

There have been a number of crash tests in which living human subjects have been exposed to low velocity crashes. In fact, we have been conducting such tests here at this institute for half a decade. Some authors have reported that minor injuries are likely to occur in collisions in which the delta V is 5 mph or above. This is based on the report of minor neck pain, headaches, or other symptoms complained of by the test subjects. However, recently our Canadian colleagues have reported that more than 30% of their test subjects experienced these minor injuries at speeds as low as 2.5 mph. It is important to understand, however, that none of these experiments were designed to establish a threshold for human tolerance to crashes and to make such an extrapolation from these experiments would be a violation of scientific method. Crash test volunteers are carefully screened to have few if any risk factors, the tests are conducted under relatively ideal laboratory conditions, and most of the tests subjects are relatively young males. And even then, some do experience some level of injury, although these do not usually require medical treatment. While these studies can tell us a great deal about crashes in general, they cannot tell us what the threshold for injury would be for, as an example, a middle-aged woman with moderate degenerative disease in her neck, who was unaware of the impending crash; or for a man with a long history of recurrent bouts of headaches and neck pain. There is no known threshold crash exposure below which injury is not possible. There is no known crash speed below which injuries cannot occur.

Q: Can someone be injured in a low speed crash?

Yes. Every day, thousands of people are injured in low speed and high speed crashes. In a large German study, in which experts actually reconstructed a large number of real world crashes, the authors reported that, of the 152 rear impacts under study, 42% were under 6.2 mph delta V. In the majority of crash tests we have conducted at this institute, in a well aligned rear impact collision between two passenger vehicles, no permanent property damage will occur in this crash range. In a recent study of low speed rear impact crashes conducted in New York, the largest category of injury crashes were graded as having no damage. In these, 38% of females and 19% of males had symptoms, which tells us something about risk as well. When damage was rated as minor, these percentages rose to 54% and 34%.

Q: Why was there a delay in the onset of my symptoms?

While numerous theories have been advanced to explain this delay, which is typically 24-72 hours, no one knows for certain. The injury is now known to involve spinal structures such as the facet joint and its ligamentous capsule, the intervertebral disc, and even the vertebral end plates. These are structures that are not supplied with a great deal of sensory nerves. In fact, up until the last decade, it was generally taught that intervertebral discs had no innervation at all. This may be one of the reasons why injuries in these tissues does not cause immediate pain. In contrast, our hands have one of the richest nerve supplies in the body in order that we can feel, tough, manipulate objects, etc. When you injure a hand, the brain becomes aware of it immediately as a result of this rich afferent innervation.

It is also known that one of the common pain producing processes in any injury is inflammation, which has cellular and humoral components. Chemical agents such as prostaglandins – which are the targets of anti-inflammatory drugs like ibuprofen-are synthesized in a cascade of chemical reactions following injury and probably do not reach peak levels in the body for 12-72 hours. This may also help to explain the common delay in onset of symptoms after whiplash or similar injury.

Q: Are males and females at equal risk of injury?

No. Females have long been known to be at just about twice the risk for injury as males in whiplash type exposures. This statistic is supported by a very large and very consistent literature. It has also been reported in several studies that females are twice as likely as males to have long-term or permanent symptoms as a result of whiplash injury. However, our own research has not found this to be true. In fact, in a case-control study of 700 persons, we found that male and female risk for poor outcome (i.e., long-term symptoms or late whiplash) was about the same. How do we explain this disparity in the literature? It is explained on the basis of a common error in data interpretation known as an ecological fallacy. Here is how it works. The studies which have caused researchers to draw the conclusion that females are more likely than males to develop long-term symptoms are of the cross-sectional study design. In this kind of study the researchers randomly query representative members of a population, asking about some subject of interest-in this case chronic pain from whiplash. In essence, it provides us with a snapshot in time of that population. Because females are more likely to be injured than males, and because females and males share the same risk of developing chronic pain once injured, any population in which males and females have similar driving habits is likely to contain significantly more females with chronic pain from whiplash: not because they are more likely to develop it, but because they are more likely to be injured in the first place. From this we can assume that males simply have a higher tolerance for trauma.

Q: Why do we call it ‘whiplash’?

Dr. H. E. Crowe, an orthopaedic surgeon, is usually credited with coining the term “whiplash” while speaking to an orthopaedic group in San Francisco in 1928. In later years he denied ever publishing the term and in 1966, he sardonically informed an audience that the definition of whiplash is “any strain of the cervical spine that doesn’t resolve until all litigation is concluded.” The term whiplash actually describes the actual mechanism of injury rather than the nature of the injury. Nevertheless, it has become part of our modern language and has even become a part of the medical lexicon. In 1995 the Quebec Task Force on Whiplash-Associated Disorders (QTF-WAD) introduced the term whiplash-associated disorders (WAD), which was intended to cover the broad range of disorders, lesions, syndromes, and conditions attributed to whiplash. However, because of the breadth of these conditions, WAD does not provide any real utility in our current vocabulary. The term “whiplash-shaken infant” is used to describe the effects of a type of very serious child abuse in which an adult violently shakes an infant back and forth. These injuries can be fatal. As a point of interest, the term “whiplash” is also used to describe the method of locomotion of sperm.

Q: I’ve had a concussion or MTBI. What is that, exactly, and what can I do? And what is the prognosis?

Mild traumatic brain injuries (MTBI) are very common and are, in fact, the most common type of brain injury today. It is estimated that there are over 2 million per year with an incidence of 200/100,000, a figure that is likely to be conservative since a large number go unreported. Motor vehicle trauma is the leading cause of all brain injuries, from MTBI to the fatal variety. MTBI implies a Glasgow Coma Scale of 13-15 points. This is a fairly crude scale used to characterize the degree of injury, but provides little ability to forecast the patient’s future. Nor does it provide us with any insight into the nature or extent of the actual injury. In fact, even today, we know little of these injuries since it is not feasible to do tissue biopsies of the brains of living subjects and because even our most sensitive diagnostic modalities such as CT and MRI often do not have the resolving power to see the sorts of injuries that can exist at the axonal level. Newer technologies such as single photon emission computed tomography (SPECT) and positron emission tomography (PET) are promising in terms of what they can tell us about the perfusion and metabolism of the brain, but the results are not yet capable of answering all of our questions. Although there is some debate regarding the nature of these injuries, it is likely that some structural injury occurs..

As to the question of what you can do, it depends on how severely you are affected. Most suffer from a variety of symptoms including forgetfulness, easy distractibility, mental fatigue, moodiness, word search, difficulty making decisions, etc. In more severe forms, personality changes may occur and be quite troublesome. For most, though, the problem is what psychiatrists refer to as a loss of divided attention.

Our brains work on a number of levels or channels. We can, for example, carry on a conversation while watching TV. For reasons not entirely clear, persons who have had an MTBI loose some of their ability to divide their attention between multiple tasks. This often results in them losing track of their own thoughts. Often, this is interpreted as forgetfulness. Several studies have demonstrated that even in persons who claim to have recovered completely from their MTBI, the typical loss of IQ is 10-14 points after such an injury, which is probably a reflection of this diminished ability to concentrate. There is also an increase in the risk of developing Alzheimer’s disease in persons who are genetically predisposed. There is a slight increased risk in the development of seizures and brain tumor, and the risk of a more severe injury in a second MTBI. We also find that some persons have more intellectual reserve than others and can weather a given brain injury better than persons with less intellectual reserve. Moreover, persons whose jobs require higher levels of intellectual functioning will often suffer more than those whose jobs are more physical and less intellectual. So, if you are rather severely affected or disabled, it might be advisable to seek the assistance of a psychiatrist or neuropsychologist familiar with brain injuries. If you are only mildly affected, and now that you understand the divided attention problem, you can make efforts to reduce the distractions in your life. Quiet work spaces and controls put on potential distractions help. Make notes of your daily plans for appointments, calls to make, etc. If you need to, write down the aisle you parked your car in. You need to think of ways to more effectively get through your day.

As for the prognosis, what we generally find is that most recovery occurs within the first six months. Beyond that, you should not expect a great deal more recovery. However, the human brain is a remarkable thing, and you can expect to compensate more effectively as time goes on.

Q: My crash was investigated by an accident reconstructionist and I was told that an injury was not possible. How can that be?

Accident reconstruction would be more correctly termed auto crash reconstruction (ACR), because there are also people who reconstruct plane, boat, and pedestrian crashes, among others, and because NHTSA has recommended that we refrain from referring to “accidents” because it implies a certain non-preventativeness or perhaps a pardonable human frailty. The fact is that more than 90% of all MVC are attributable to human error. ACR can often provide critically important details of a crash that can have profound implications. For example, a cursory or simple examination of a crash scene often does not allow us to know who was driving, or which car crossed the double yellow line inappropriately, or who was speeding, etc. Yet these details are very important to heirs of victims, to insurance companies, to law enforcement, etc. ACR can provide the clues needed to decide guilt or innocence, culpability or exoneration.

In the last decade, ACR has been used to investigate the low and moderate speed crashes from which spring allegations of various soft (connective) tissue injury and other conditions. Unfortunately, although ACRs apply the same principles of physics in these crashes, nearly all of the values used in the calculations are necessarily educated guesses at best since there is very often limited physical evidence to measure after these crashes. Moreover, risk assessment should consider not only a thorough medical history of the subject, but also a thorough assessment of known risk factors that might have played a part. What is most interesting is the change in the purpose of ACR. Where before it was typically to answer questions about which driver was at fault, today it has evolved into a tool for gauging the likelihood of injury risk. This is particularly interesting in light of the fact that the subjects are usually evaluated by one or more physicians. Thus, ACR, to some degree, has transmogrified into an instrument of risk assessment for which it has limited validity. For example, there have been no scientific validation studies designed to test the claims of accuracy or reliability of low speed ACR in the context of risk assessment. And, judging from our experience in these crash tests, it is not likely that such accuracy or reliability can be proved. There are simply too many unknowns and too little physical evidence from which to work. Moreover, it is likely that a larger portion of risk is related to the occupant’s position in the vehicle, level of awareness of the impending crash, age, sex, and medical history. Thus, it is not only unlikely that ACR can determine crash metrics after the fact with a high degree of scientific reliability or accuracy, but there there is also a serious question as to whether knowing these crash metrics would allow the ACR to determine what kinds of injuries would occur, if any, and how severe they would likely be in any given individual. Currently, there is virtually no scientific evidence or support for this contention. In our opinion, it is remarkable that this is occurring across the U.S. on a daily basis without stronger legal or scientific challenge.

 

Still have questions? Call Herndon Chiropractic and we’ll get right back to you.


Dr. Devinder P. Singh | Herndon Chiropractor | (703) 464-5597

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