Epidemiology of Whiplash Injuries
Epidemiology has been defined as “the science concerned with the study of the factors determining and influencing the frequency and distribution of disease, injury, and other health-related events and their causes in a defined human population for the purpose of establishing programs to prevent and control their development and spread. Hence, this chapter will cover the numbers of persons who experience whiplash injuries, mainly in the United States, as well as factors that are thought to influence the risk of becoming injured in a motor vehicle crash (MVC) or of developing chronic symptoms post-injury. Many such factors have been suggested, including the injured person’s age, gender, anthropometry, certain pre-existing conditions, position within the vehicle, the vehicle’s crashworthiness, and others. Clinicians should be familiar with the significant risk factors in order to formulate more personalized treatment plans and prognoses in whiplash patients.
Epidemiological studies have been used extensively to investigate the whiplash phenomenon, primarily because the condition is not amendable to investigation using randomized controlled trails, which are considered to be the gold standard of which are considered to be the gold standard of clinical research. This is primarily because it would be unethical to expose people to the kinds of forces that are capable of causing injuries involved in MVCs. Thus, whiplash studies typically compare a group of people who have already been involved in MVCs with another group who have not. Researcher wither follow the groups forward in time (ie, cohort studies) or assess various aspects of their medical history retrospectively, before as well as after the time of the crash (ie, case-control studies).
Studies have been carried out where human volunteers were exposed to whiplash-like forces (ie, crash tests) similar to what would be expected in a real-life MVC. However, they have always simulated relatively low-speed crashes and rarely resulted in symptoms. When symptoms did occur, they have been mild and short -lived. Also, these types of studies have never randomized subjects to groups for comparisons.
Epidemiology is commonly used in the field of public health, which focuses on the study of populations with the purpose of identifying the causes of diseases and conditions. Once the causes are identified, strategies can be developed that are designed to prevent the diseases from occurring. Public health interventions, such as advising people about the best ways to avoid risk factors or how they can integrate protective factors into their lifestyles, can effectively prevent future injuries and illness, as well as enhance the healing process when injury or illness has already occurred. Traffic safety matters, including whiplash, are of interest to public health practitioners, health care providers, as well as local, state, and national governments because of the potential to prevent or reduce the severity of crash-related injuries using these preventive methods.
One aspect of epidemiology involves collecting data from various sources and then analyzing it. However, the data pertaining to the epidemiology of whiplash is at times conflicting--sometimes because of inconsistencies in the way the data were gathered and other times in the way they were analyzed. It is also possible, and not that uncommon, for data collection and analysis to go awry at the same time. These inaccuracies can often be resolved by relying on higher-quality information sources, though even high-quality sources are not always in agreement. In addition to the potential flaws associated with the collection, analysis, and reporting of data, the way data are interpreted is often inconsistent. This chapter will call attention to some of these controversial aspects in relation to whiplash, relying on the highest-quality studies available.
Not only is the way data are collected and interpreted inconsistent in this area of investigation, the term “whiplash” itself is controversial: whereas some researchers use it to describe a mechanism of injury in which the head and neck are forcibly moved beyond the limits of anatomical integrity, others use it to describe the injury that often results. Consequently, the Quebec Task Force on Whiplash-Associated Disorders coined the term “whiplash-associated disorders” (WAD) in 1995 to describe an array of symptoms that have been reported in association with whiplash injuries. According to the Quebec Task Force, WAD symptoms may include neck pain and stiffness, headache, dizziness, tinnitus, memory loss, deafness, dysphasia, upper extremity syndromes (e.g., radicular symptoms and carpal tunnel syndrome), Temporomandibular joint disorder, and others.
Basic Epidemiological Terms
There are some basic terms that are essential to the understanding of the science of epidemiology, a few of which are listed here.
Association-when two or more attributes are related to each other in such a way that they change predictably together.
Bias-anything that causes the conclusions of a study to be systematically different from the truth. Bias may occur in the way data are collected, analyzed, and/or interpreted.
Case-a person in an epidemiological study who has the disease or condition under investigation. These persons are members of the cases group in a case-control study.
Case-control study-a type of epidemiological study in which participants are separated into two groups: members of one group have the disease of condition under study (the cases), and those in the other group do no (the controls). The groups are assessed concerning previous exposure to various factors or the presence of certain traits, and then rates of exposure/traits are compared between cases and controls.
Cause-refers to a factor that has a direct effect on the occurrence of a disease or condition. The factor could be an intrinsic trait or a behavior of the persons being studied or some event they were exposed to
Cohort--A distinct group of people who have something in common, such as being exposed to a common risk factor or being born in the same year.
Cohort study--a type of epidemiological study that follows one or more cohorts forward in time to determine the incidence of new diseases, conditions, and/or deaths that occur. Typically, one cohort is exposed to a risk factor, while the comparison cohort is not. The rates of the measured outcomes are then compared between the groups to see if members of the exposed cohort are more likely to develop the disease or condition.
Exposure--an external factor that may have an impact on the health of a person if the person is exposed to that factor.
Incidence--the number of newly diagnosed cases of a disease within a specified population during a specified time period, which is typically 1 year. The denominator is the population under consideration and the numerator is the number of new cases that develop during the given time period. The incidence rate may be calculated by dividing the number of the new cases of a disease in a given time period by the number of persons in the population who are at risk for the disease.
Odds ratio (OR)--an estimate of the odds of developing a disease given that a person was exposed to a relevant risk factor. It is the odds of being exposed to the risk factor under investigation in the cases in the control group, which is calculated from data in case-control cases.
Prevalence--the number of persons in a population who may have a given disease or attribute at a particular point in time (point prevalence) or over a specified period of time (period prevalence). The prevalence rate is calculated by dividing the total number of cases of a disease within a population by the total population.
Relative risk (RR)--the probability of disease being present in the exposed group, divided by the probability of disease in the unexposed group, which is commonly calculated in cohort studies
Risk--the likelihood that a person will experience a given event (e.g., become injured).
Risk factor--a behavior, environmental exposure, or inherent characteristic of an individual that increases the likelihood of an individual’s developing a disease or condition.