U.S. flag

An official website of the United States government

NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.

Laskowitz D, Grant G, editors. Translational Research in Traumatic Brain Injury. Boca Raton (FL): CRC Press/Taylor and Francis Group; 2016.

Cover of Translational Research in Traumatic Brain Injury

Translational Research in Traumatic Brain Injury.

Show details

Chapter 1Epidemiology

and .


Traumatic brain injury (TBI) is an important public health concern that is one of the leading causes of death and disability annually around the world.1,2 Several factors have fueled increasing interest in TBI over the last several years, including rising awareness around the acute and chronic effects of sport-related concussion (SRC) and the reported incidence of head injuries sustained by U.S. military service members deployed to Iraq and Afghanistan. Sporting and military cohorts are now known to be at elevated risk of mild TBI (mTBI), characterized by more subtle neurocognitive and neurobehavioral symptoms that are often challenging to assess and characterized in a clinical setting.

A strong epidemiological framework for TBI is vital to improving our understanding of the injury’s occurrence, populations at risk, and effective strategies for injury prevention. The purpose of the current chapter is to review the most recent epidemiological literature on TBI in both civilian and military populations.

The epidemiological literature on TBI is limited by a number of factors, not the least of which is that the definition of a TBI varies across studies. Though there are a number of operational definitions, TBI is commonly and most basically defined as an alteration in brain functioning or the emergence of evidence of brain pathology caused by an external force.3 One of the methodological limitations of many epidemiological studies over the last 20 to 30 years has been suboptimal or inconsistent classification and inclusion criteria. Many studies have included individuals who sustained an injury to the head that may not have involved any alteration in brain function or physiological damage to the brain. For example, Bazarian and colleagues used emergency department records for a study of mTBI that included individuals with diagnostic codes such as “skull fracture,” “intracranial injury of unspecified nature,” and “head injury, unspecified.”4 Even though many individuals with these diagnoses likely met the criteria for mTBI, there are others who did not sustain a TBI at all or may have sustained an injury that was more severe than an mTBI.

Population-based epidemiological studies are typically based on hospital admission or discharge records, emergency department records, or death certificates, which creates a selection bias.5 It has long been held that many patients with less severe injuries do not present for medical treatment and therefore are not included in many of these studies. In addition, changes in hospitalization patterns over the past several years, with fewer less severe patients being hospitalized, has also likely lead to an underestimation of the true incidence of milder forms of TBI (for a review, see the study by McCrea6).

TBI severity classification can also vary among different studies. Commonly, clinical indicators related to acute injury characteristics are used to indicate injury severity such as mild, moderate, or severe. The indicators most commonly used are alteration in consciousness, loss of consciousness (LOC), and post-traumatic amnesia (PTA) following the injury. The Glasgow Coma Scale (GCS) is the most commonly used clinical tool for assessing consciousness following an injury.7 A GCS score of 13 to 15 is considered a mild injury, 9 to 12 is considered a moderate injury, and 8 or less is considered a severe injury. Methods used to classify TBI also have varied utility. The GSC as a highly effective tool to differentiate the severity of TBI has been well founded and the GCS has been shown to be useful in predicting morbidity and mortality in more severe injuries,710 but it has been less useful as a prognostic indicator for mTBI.11 Historically, not all epidemiological studies have employed a common or standardized classification system, which complicates interpretation of epidemiological data and comparisons across studies.

In terms of injury reporting, there is no single system in the United States or most other countries that tracks the occurrence of head injury over large populations. As a result, a true appreciation for TBI’s national or worldwide incidence is lacking. The Centers for Disease Control and Prevention (CDC) is the most comprehensive data source of epidemiological studies of TBI in the United States, as it monitors death records (National Vital Statistics System), hospitalizations (National Hospital Discharge Survey), and emergency department visits (National Hosptial Ambulatory Medical Care).12 The data for military TBI injuries comes from the Department of Defense (DoD) in collaboration with the Armed Forces Health Surveillance Center.13 Where available, other sources from well-designed epidemiological studies in the United States and around the world were also reviewed.

The first section of the this chapter will review the civilian literature, including sport-related concussions, and the second section will focus on the military epidemiological literature.



According to the most recent figures from the CDC, the average estimated incidence of TBI in the United States between the years 2002 and 2006 was 1,691,481 (576.8 per 100,000). Of these 1,364,797 (465.4 per 100,000) were treated in the emergency department (ED) and released; 275,146 (93.8 per 100,000) were hospitalized and discharged alive; and 51,538 (17.6 per 100,000) died.12 Earlier examination of CDC data between 1995 and 2001 estimated a total of 1,396,000 (506.4 per 100,000) TBIs each year with 1,111,000 (403.1 per 100,000) ED visits, 235,000 (85.2 per 100,000) hospitalizations, and 49,900 (18.1 per 100,000) deaths.14 These data from the CDC do not include individuals that were treated at outpatient facilities or who did not seek treatment.

Previous reports from the United States that used the 1991 National Health Interview survey of 46,761 households estimated there were approximately 1.5 million (618 per 100,000) individuals who sustained nonfatal brain injuries in the United States and of those approximately 25% did not seek any type of treatment.15 Comparison between the Sosin and colleagues report15 and the reports from the CDC data are difficult to make based on methodological differences. However, comparison between the CDC reports from Langlois and colleagues14 to that of Faul and colleagues12 clearly shows that the average annual estimate of ED visits and hospitalizations has increased but the rate of TBI related deaths has decreased. This was investigated more closely in a report of death rates from 1997 to 2007 that showed an 8.2% decrease, from 19.3 to 17.8 per 100,000, during this time and the authors noted that this follows a long-standing trend of decreases in TBI-related deaths over time.16

A review of European epidemiological studies by Tagliaferri and colleagues found a wide range in the incidence in TBI.17 The authors reviewed 23 epidemiological reports from various European countries between 1980 and 2003. Methodology varied considerably between the studies, as did the estimated rates of TBI. One study from a province of Spain estimated an annual average to be 91 per 100,000, whereas a study from Sweden estimated 546 per 100,000. The authors removed the extreme reports from the study and found an aggregate of 235 per 100,000 TBIs annually.

The aforementioned studies constitute some of the best epidemiological data on incidence of TBI, but the data likely grossly underestimates the incidence of mTBI.5 A World Health Organization (WHO) systematic review of the mTBI literature found that 70% to 90% of TBI was mild in nature and that hospital-treated mTBI was approximately 100 to 300 per 100,000 in the studies it reviewed. However, given the undertreatment and reporting of mTBI, the WHO estimated that the true yearly incidence was likely 600 per 100,000.18

A population-based study in New Zealand attempted to correct for underreporting by using both prospective and retrospective surveillance systems in an attempt to register all instances of TBI over a 1-year period between March 2010 and February 2011. The study was based in the city of Hamilton, which has a population of 129,249 and the surrounding rural area with a population of 43,956. The investigators reportedly enrolled all healthcare providers (e.g., family physicians, health centers, hospitals, ambulance services), the local prison, community services (e.g., school, sports clubs), and used national healthcare databases and the death registry to assist in identifying cases. Regular contact was kept among these sources throughout the year and each identified case was crosschecked to ensure there were no duplicates. During this time, 1369 TBIs were identified, which the authors concluded to be an annual incidence rate of 790 per 100,000.19 This rate is considerably higher than most epidemiological studies and the authors asserted that this was due to a larger number of mild traumatic brain injuries captured that typically go unaccounted for in most other epidemiological studies.


Data regarding the severity of TBI is difficult to ascertain, given that classification systems are not consistent across studies or sometimes even within studies. It is commonly accepted that the majority of TBIs are mild in severity and make up between 70% and 90% of all TBIs.20 This number is likely an underestimation, given that many mTBIs are thought to go untreated and therefore unreported. In Feigin and colleagues,19 mTBI made up nearly 95% of the total sample. Another confounding factor when considering injury severity is that individuals who sustained more significant brain injury or other trauma are commonly sedated, which complicates injury classification. In one study of adults receiving inpatient rehabilitation services, 19.2% of the sample was classified as severe, 10.3% was moderate, and 16.4% of the sample was chemically sedated. The injury severity and reason for sedation in those individuals is not entirely clear, although the authors indicated that most were thought to be in the severe range.21

In addition to underestimating the number of mild injuries, the current epidemiological literature likely overestimates the number of severe injuries as many studies utilize hospital admission records to classify injury. Similar to Cuthbert and colleagues,21 studies that utilize hospitalization records report that 20% of injuries are classified as severe22 while other authors reported that 80% of hospitalized individuals sustained mild injuries, 10% sustained moderate injuries, and 10% were severe. These figures are considerably higher than the report by Feigin and colleagues,21 and also well above a review of European epidemiological studies that calculated a TBI severity ratio of 22:1.5:1 for mild, moderate, and severe injuries, respectively.

Risk Factors and Characteristics


A consistent finding across the epidemiological literature is that TBI is much more frequent in males than females. According to the most recent CDC data, males were 1.4 times more likely to sustain a TBI, as they had an estimated average annual TBI rate of 998,176 compared to 693,329 for females. Of the TBIs sustained by males, approximately 17% lead to hospitalization and 4% were fatal injuries. In comparison, approximately 15% of the females were hospitalized and less than 2% died following TBI. The rate of TBI in males was greatest across all age groups.12 The ratio reported by the CDC is largely consistent with previous findings from United States data, which showed a male to female rate of 1.6:123 and also European studies that ranged from 1.46:124 to 1.8:1.25 It should be noted that most European epidemiological studies had a bias toward more severe injuries, which may have inflated the estimate relative to the United States samples. Feigin and colleagues found a male to female rate ratio of 1.67:1 in a population based sample that captured a significant number of more mild injuries, so it may be that the CDC data is a slight underestimate.19


According to the most recent data from the CDC, TBI rates are highest among young children age 0 to 4 (1337.3 per 100,000) and older adolescence aged 15 to 19 (896.2 per 100,000). Older adults aged 75 and above also have a high rate of TBI (932 per and they account for the highest rate of TBI-associated hospitalizations (339.3 per 100,000) and death (56.6 per 100,000). To give a point of comparison, the rate of hospitalization in the most elderly was over 3.5 times the rate of hospitalization of the total sample (93.8 per 100,000) and the death rate was over 3 times greater than that of the total sample (17.6 per 100,000). This pattern of high rates of TBI in early childhood, late adolescence, and in the elderly has been shown in many population-based studies.1

Race and Ethnicity

Some studies show higher incidence of TBI in non-whites compared to whites, but this is somewhat controversial given methodological inconsistencies and the quality of the data used to generate these findings. According to the most recent data from the CDC that looked at emergency department visits, African Americans had the highest rate of TBI (618.6 per 100,000), followed by whites (448.3 per 100,000), and then American Indians/Alaska Natives/Asians or Pacific Islanders (334.7 per 100,000).12


The positive association between blood alcohol concentration (BAC) and many types of injuries is well established. In terms of brain injury, it has been shown that a high percentage of individuals seek medical attention following a TBI have a positive BAC, with figures ranging from 56% to 72% in various United States samples.26 In addition, a large number of those individuals (36% to 55%) were legally intoxicated at time of injury.2730 European epidemiological studies also show a strong relationship between alcohol consumption and TBI, though the figures are less consistently high as the data from U.S. populations, with reports ranging from 24% to 51% who were positive for alcohol.17 Langlois and colleagues reported that alcohol use was reported in 21% of motor vehicle occupants hospitalized with a TBI, and over 12% had a BAC above the legal limit.31

Recurrent TBI

Recurrent TBI, especially mTBI, has become a topic of considerable interest in recent years due to concern that TBI increases the risk of cognitive impairment later in life32 or possible neurodegenerative conditions.33 Though skepticism exists regarding the link between mTBI and the development of neurodegenerative conditions34 it has been shown that recurrent mTBI is associated with prolonged recovery and that athletes who have a history of mTBI may be at greater risk of sustaining future injuries.35 Annegers and colleagues conducted the first population based study of recurrent TBI and found that the relative risk of a second TBI among those with an earlier TBI was 2.8 to 3 times greater than the noninjured sample.36 Additionally, in those that sustained a second head injury the risk of sustaining a third head injury was 7.8 to 9.3 times that of an initial head injury in the population. Recurrent TBI has been found to be related to alcohol abuse in a number of studies22 with one study indicating that if an individual’s first injury after age 12 was alcohol related they were at a fourfold greater risk of repeat head injury by age 34. Recurrent TBI has long been a concern in sports with a recent epidemiological study of sport concussion in high school athletes in the United States showing that 13.2% of all concussions were recurrent, and consistent with previous findings the symptoms of recurrent concussion took longer to resolve.37

External Causes

According to the most recent data from the CDC, falls are the most common cause of TBI, with an estimated annual average of 523,043. The rate of fall-related TBI was greatest among children aged 0 to 4 years (839 per 100,000) and adults age 75 and older (599 per 100,000). Falls accounted for approximately half of the TBIs in children age 0 to 14 and approximately 60% of adults aged 65 and older. The second most common cause is motor vehicle traffic accidents (estimated annual average 292,202), followed by struck by/against events (estimated annual average 169,625) and assault (estimated annual average 169,625).12 Motor vehicle accidents resulted in the largest percentage of TBI-related deaths at 31.8%.

Few European epidemiological studies have investigated external causes, but most reports indicate that motor vehicle accidents are the most common events leading to TBI, followed by falls.17 It should be noted that the external cause of TBI varies considerably by country due to a myriad of factors, including economic status. Lower and middle-income countries that had not had access to motor vehicles are showing sharp increases in motor-vehicle-related injuries and deaths, while wealthier countries are developing better safety standards and road laws that have led to a decrease in motor-vehicle-related mortality over the years.38 These factors need to be better understood to understand the epidemiological impact of TBI around the world.

TBIs related to engagement in sports and recreational activity are a major cause of TBI, but are likely underreported in the literature given that most of the injuries are mild in severity and untreated. Previous epidemiological studies estimated approximately 300,000 sports-and recreation-related TBIs per year.39 However, it has been noted that Thurman and colleagues39 only included TBIs for which the person reported a loss of consciousness, which is considered a very small minority (10%) of TBIs related to sports and recreation.40,41 Langlois and colleagues indicated that if all injuries are taken into account, including those who do not seek medical attention, a more accurate estimate of 1.6 to 3.8 million sports-and recreation-related concussions occur annually.2 The data on sports-related concussion is likely to improve in the coming years as identification of concussion by athletic trainers, coaches, athletes, and medical personnel improves and more athletes seek treatment. A recent study of emergency departments found that sports-related concussion visits doubled for children aged 8 to 13 and increased by more than 200% in individuals aged 14 to 19 from 1997 to 2007.42

Abusive head trauma is the leading cause of serious head injury and death in children age 2 years and younger. Keenan and colleagues prospectively collected data from nine hospital pediatric intensive care units from January 1, 2000, to December 31, 2001.43 Results showed that the incidence of inflicted TBI in the first 2 years of life was 17 per 100,000 person-years, with infants having a higher incidence (29.7 per 100,000) relative to children in the second year of life (3.8 per 100,000). To determine whether an injury was inflicted the authors relied on confession from the parents or medical/social service determination of abuse so it is likely that these are underestimates of the true incidence. A more recent study using a national sample of inflicted injury in children found a slightly higher rate of 18.7 per 100,000 for children less than 2 years of age.44

TBI associated with violence against adults is also underreported and underidentified due to many factors, including low reporting rates in domestic violence and other factors associated with the types of trauma sustained during assaults.22 Previous data from the CDC estimated that at least 156,000 TBI-related emergency department visits, hospitalizations, and deaths each year are associated with all types of assaults2 with more recent estimates showing approximately 169,625 TBIs per year. According to these data, assaults account for approximately 10% of total TBIs.12 A study based on the New Zealand population found that assaults comprised almost 17% of all TBIs with an estimated annual incidence of 132 per 100,000,19 which is considerably higher than estimates from the United States. According to the CDC data, the highest risk of sustaining a TBI secondary to assault is in individuals age 15 to 44, as this age group comprises 75% of assault-related head injuries.12

Lifetime Prevalence

The lifetime prevalence of TBI is less well studied in the epidemiological literature due primarily to the methodology employed by most studies. Lifetime prevalence of TBI refers to the number of individuals who have ever experienced a TBI. In a large-scale study, Winqvist and colleagues used a birth cohort design of individuals born in two provinces of North Finland in 1966.45 The entire cohort included 12,058 residents who were followed through age 34. Results showed that the average annual incidence of TBI was 118 per 100,000 and by age 35, 3.8% of the cohort had experienced at least one hospitalization for TBI.45 The study only included hospital and health center discharge records with outpatient services and emergency department visits of less than 24 hours being excluded from analysis, so these data are only capturing more severe injuries. A birth cohort study in New Zealand that used any type of medical attendance where TBI was diagnosed and followed through age 25 found a much higher average annual incidence rate of 1750 per 100,000. By age 25, 31.6% of the cohort had received a TBI for which they received medical care.46 In a study by McKinlay and colleagues, only 32.9% of the individuals who sustained a TBI were admitted to the hospital for further observation or treat-ment.46 Retrospective self-report studies by Anstey and colleagues47 and Silver and colleagues48 that looked at TBI with loss of consciousness indicated a lifetime prevalence rate of 5.7% to 8.5%, respectively.

Consequences of TBI

Due in large part to advances in medicine and safety, more people are surviving TBI than ever before. Estimates of individuals in the United States who are living with long-term or lifelong disability associated with a TBI range from 3.2 million to 5.3 million.2,49 These estimates only include individuals who were hospitalized as a result of their injuries and therefore are biased toward more severe injuries. The Glasgow Outcome Scale (GOS) is an unsophisticated but widely used indicator of disability or residual effects used by hospitals at the time of discharge. The major classifications of the GOS are death, persistent vegetative state (i.e., patient exhibits no obvious cortical function), severe disability (i.e., patient is conscious but requires daily support due to disability), moderate disability (i.e., disabled but independent in regard to daily living needs), and good recovery (i.e., resumption of normal activities) though minor neurologic and psychological deficits may be present.50 Data from a 14-state CDC-funded TBI surveillance study found that 17% of hospital discharges were reported as having moderate to severe disability based on the GOS.31 Krause and colleagues estimated that the total number of disabilities from new brain injuries for the year 2000 was 98,560 or a rate of approximately 35 per 100,000 of the population.26 A population-based sample of persons with TBI from the South Carolina Traumatic Brain Injury Follow-up Registry was used to develop a predictive model of TBI that estimated 43.3% of hospitalized TBI survivors in 2003 experienced TBI-related long-term disability, which in turn estimated that 124,626 Americans per year who likely need rehabilitative or supportive services following a TBI.51

Disability associated with mTBI is difficult to calculate given that only about 10% are hospitalized and therefore not considered in many epidemiological studies. However it has been well established that mTBI results in physical, cognitive, psychological, and social dysfunction that leads to lost productivity and decreased quality of life (for a review, see McCrea6). The impact on occupation has been reported to be comparable to general trauma patients relative to the duration of time off work and reported problems upon returning to work.52 Boake and colleagues showed that most mTBI patients treated and released from emergency departments did not return to work until 1 to 3 months after the injury and there was virtually no difference between those who were treated and released from the emergency department (46% working at 1 month, 66% at 3 months, and 68% at 6 months) versus those who were hospitalized (39% working at 1 month, 62% at 3 months, and 71% at 6 months).52

Economic Cost

The real economic cost of TBI is difficult to calculate given the number of untreated TBIs that may lead to missed workdays or decreased productivity at work. Additionally, it is difficult to truly appreciate and quantify the impact that TBI has on caregivers and family members. Langlois and colleagues22 extrapolated data from Finkelstein and colleagues53 to calculate the estimated economic burden of TBI in 2009 dollars. The authors estimated that the total costs of fatal, hospitalized, and nonhospitalized TBI in the United States totaled more than $221 billion, including $14.6 billion for medical costs, $69.2 billion for work lost costs, and $137 billion for the value of lost quality of life.22 A report by the CDC indicated that the economic burden of TBI in the United States was estimated to be $56 billion, with mTBI accounting for $16.7 billion of that figure.54


TBI has been referred to as the “signature injury” among U.S. service members serving in the conflicts in Iraq (Operation Iraqi Freedom, OIF) and Afghanistan (Operation Enduring Freedom, OEF).55 The identification of moderate and severe TBI is not complicated even in the war theater given the clear clinical signs and symptoms. Accurate identification of mTBI can be a challenge given the sometimes relatively subtle nature of the symptoms, the lack of diagnostic tools with good sensitivity and specificity that can be used during combat, and the significant symptom overlap with other conditions such as post-traumatic stress disorder (PTSD).56 One study investigating the co-occurrence of TBI with psychiatric disturbance and pain found that of the service members diagnosed with TBI, 89% also had a psychiatric diagnosis with the most frequent being PTSD at 73%. In the TBI sample, 70% also had a diagnosis of head, back, or neck pain.57

Surveillance data of military TBI are primarily available through the Department of Defense (DoD) in cooperation with the Armed Forces Health Surveillance Center. It should be noted that data from the DoD reports comprise TBI data that occurred anywhere in the world U.S. forces are located, not just deployed servicemen. The DoD reported that 80% of the injuries that are reported occur in nondeployed settings with common causes being crashes in privately owned and military vehicles, falls, sport and recreation activities, and military training.13

The DoD data subtypes TBI into four classifications according to specific criteria.

  • 1. Concussion/mTBI—A confused or disoriented state that lasts less than 24 hours; loss of consciousness (LOC) for up to 30 minutes; post-traumatic amnesia (PTA) lasting less than 24 hours; and structural brain imaging (MRI or CT) that is read to be normal.
  • 2. Moderate TBI—A confused or disoriented state lasting over 24 hours; LOC for more than 30 minutes, but less than 24 hours; PTA lasting greater than 24 hours but less than 7 days; and structural brain imaging that shows normal or abnormal results.
  • 3. Severe TBI—A confused or disoriented state that lasts more than 24 hours; LOC for more than 24 hours; PTA for more than 7 days; and structural brain imaging yielding normal or abnormal results.
  • 4. Penetrating TBI—Any head injury in which the dura mater is penetrated.


According to the most recent report by the DoD, there have been a total of 294,172 TBIs from 2000 through the fourth quarter of 2013.13 The most common injury is concussion/mTBI, which accounted for 242,676 (82.5%) of the injuries, followed by moderate TBIs (23,754; 8.1%), not classifiable (20,433; 6.9%), penetrating (4389; 1.5%), and severe (2920; 1%). When the individual years are considered, the total prewar incidence of TBI was 10,958 for 2000. The years following the commencement of OEF were not considerably different, with subsequent increases of about 3% to 9% each year until 2006, when 17,037 injuries were reported. The number of injuries increased drastically in 2007, when 23,217 injuries were reported, which was an increase of approximately 36% from 2006. Another considerable increase of 22% was recorded the following year (28,877 injuries in 2008). TBI rates continued to increase until a peak in 2011 of 32,625 injuries, and then there was a slight decline in 2012 (the last full year of available data), when 30,406 TBIs were reported.

The distribution of injury type has not drastically changed since the start of OEF, with the vast majority (71% to 86%) of injuries being concussions/mTBI. The increase in TBI since the start of OEF has been driven almost exclusively by large increases in the concussion/mTBI group. According to prewar data in 2000, there were 275 penetrating injuries, 178 severe, 1616 moderate, and 7179 mild TBIs. In comparison, there were 324 penetrating, 261 severe, 1857 moderate, and 27,535 mild TBIs recorded in the year 2011, which had the highest rate of total TBIs. When the year 2011 and 2000 are compared, substantial increases are noted across injury types, including penetrating, severe, and moderate TBI, with increases of approximately 17%, 47%, and 15%, respectively. However, the most substantial increase, and what accounts for the large increase of total TBIs, was concussion/mild TBI injury that showed a 283% increase 2000 to 2011. This increase is probably at least partially accounted for by better identification and diagnosis of these less severe injuries. In any event, it is clear that concussion/mTBI has the largest scale impact on our service members.

External Causes

The mechanisms of injury for military personnel are generally similar to those found in civilians and include motor vehicle accidents, falls, sports/recreation related, assaults, and collisions with objects. According to a review by Langlois and colleagues,22 mechanism of injury data is typically only available for hospitalizations and is provided by the Armed Forces Health Surveillance Centers (AFHSC). Upon review of the data from the AFHSC, the authors showed that during the prewar period, land transport (~25%) and falls/miscellaneous (~24%) were the most common injury type followed by sports/recreation (9%) and nonbattle assaults (7%) among active-duty servicemen.22

Injury data for deployed servicemen is difficult to attain, as this data is not included in the DoD reports. A study of an Army unit (3973 servicemen) following a 1-year deployment in Iraq identified 907 soldiers diagnosed with a TBI. According to survey data, TBI was most commonly caused by blast (88%) followed by motor vehicle accidents (39%), falls (20%), fragments (15.8%), and bullets (3.1%). The servicemen in the study commonly identified more than one cause of their injury, which led to the percentages being greater than 100.58 Blast injury was clearly the most commonly reported mechanism of injury, and the high rate of blast injury is reported elsewhere.59,60 It is now commonly held that a dual mechanism (blast and blunt) is common in the military environment.

There are several mechanisms of blast injury described in the literature, including primary, secondary, tertiary, and quaternary. Primary injuries are due to overpressurization or underpressurization shock waves caused by explosions. The shock waves move through the body from solid-and liquid-filled sections to gas-filled organs (e.g., lungs), which causes damage to the organs. Secondary injuries are due to fragments and projectiles from explosions. Tertiary injuries are caused by a displacement of air (blast wind), throwing the individual and causing them to collide with an object. Quaternary injuries are those not classified by the other three and include toxic inhalation, burns, and crush injuries.61 The exact nature of the blast injury is not typically identified, but it is clear that most are likely caused by secondary and tertiary injuries as these involve a mechanical component similar to other TBI-causing mechanisms.62 TBI related to primary blast injuries has been reported in the literature,63 but this remains controversial given the exact mechanism of injury remains unclear.64 Given the specific context in which blast injuries occur and the lack of reliable data regarding acute injury characteristics and mechanism of injury, these injuries are difficult to study and the epidemiological data is lacking. Future research is required, ideally employing a standard definition of injury and robust injury surveillance systems.


TBI is one of the most significant public health problems in the United States and worldwide based on incidence, prevalence, healthcare resource utilization, resulting death and disability, and total economic cost. The highest rates of TBI are observed in the very young and very old, males, minorities of low socioeconomic status, and substance abusers. The overwhelming majority of TBIs are categorized as mTBI. Determining the true incidence of mTBI has been hampered by a multitude of methodological factors (e.g., variable injury definitions and criteria, surveillance systems, research setting). Athletes competing in contact/collision sports and military service members are at particularly higher risk of mTBI, and, in some instances, the potential for recurrent injury. Traditional means for classifying TBI severity have limited utility in detecting and categorizing mTBI, which has significant implications to epidemiologic research. Multidimensional definitions that incorporate information on biomechanics, acute injury characteristics, clinical signs, and symptoms result in the most accurate diagnosis of mTBI. These methods provide promise for future studies to further clarify the true epidemiology of TBI, which in turn will guide development of clinical endpoints for diagnostic and outcome studies.


Hyder A.A. et al. The impact of traumatic brain injuries: A global perspective. NeuroRehabilitation. 2007;22(5):341–353. [PubMed: 18162698]
Langlois J.A, Rutland-Brown W, Wald M.M. The epidemiology and impact of traumatic brain injury: A brief overview. J Head Trauma Rehabil. 2006;21(5):375–378. [PubMed: 16983222]
Menon D.K. et al. Position statement: Definition of traumatic brain injury. Arch Phys Med Rehabil. 2010;91(11):1637–1640. [PubMed: 21044706]
Bazarian J.J. et al. Mild traumatic brain injury in the United States, 1998–2000. Brain Inj. 2005;19(2):85–91. [PubMed: 15841752]
Andelic N. The epidemiology of traumatic brain injury. Lancet Neurol. 2013;12(1):28–29. [PubMed: 23177533]
McCrea M. Oxford: Oxford University Press; 2008. Mild Traumatic Brain Injury and Postconcussion Syndrome: The New Evidence Base for Diagnosis and Treatment.
Teasdale G, Jennett B. Assessment of coma and impaired consciousness. A practical scale. Lancet. 1974;2(7872):81–84. [PubMed: 4136544]
Dikmen S.S. et al. Neuropsychological outcome at 1-year post head injury. Neuropsychology. 1995;9(1):80–90.
Jane J.A, Rimel R.W. Prognosis in head injury. Clin Neurosurg. 1982;29:346–352. [PubMed: 7172555]
Klauber M.R. et al. The epidemiology of head injury: A prospective study of an entire community—San Diego County, California, 1978. Am J Epidemiol. 1981;113(5):500–509. [PubMed: 7223731]
Cappa K.A, Conger J.C, Conger A.J. Injury severity and outcome: A meta-analysis of prospective studies on TBI outcome. Health Psychol. 2011;30(5):542–560. [PubMed: 21875208]
Faul M. Traumatic Brain Injury in the United States: Emergency Department Visits, Hospitalizations and Deaths 2002–2006. Atlanta, GA: Centers for Disease Control and Prevention, National Center for Injury Prevention and Control.; 2010.
2013. Department of Defense. DoD Worldwide Numbers for TBI. Retrieved April 15, 2014. Available at http://dvbic​.dcoe.mil​/dod-worldwide-numbers-tbi.
Langlois J.A, Rutland-Brown W, Thomas K.E. Traumatic Brain Injury in the United States: Emergency Department Visits, Hospitalizations, and Deaths. Atlanta, GA: US Center for Disease Control and Prevention.; 2004.
Sosin D.M, Sniezek J.E, Thurman D.J. Incidence of mild and moderate brain injury in the United States, 1991. Brain Inj. 1996;10(1):47–54. [PubMed: 8680392]
Coronado V.G. et al. Surveillance for traumatic brain injury-related deaths—United States, 1997–2007. MMWR Surveill Summ. 2011;60(5):1–32. [PubMed: 21544045]
Tagliaferri F. et al. A systematic review of brain injury epidemiology in Europe. Acta Neurochir. 2006;148(3):255–268. discussion 268. [PubMed: 16311842]
Carroll L.J. et al. Prognosis for mild traumatic brain injury: Results of the WHO Collaborating Centre Task Force on Mild Traumatic Brain Injury. J Rehabil Med. 2004;43 (Suppl):84–105. [PubMed: 15083873]
Feigin V.L. et al. Incidence of traumatic brain injury in New Zealand: A population-based study. Lancet Neurology. 2013;12(1):53–64. [PubMed: 23177532]
Cassidy J.D. et al. Incidence, risk factors and prevention of mild traumatic brain injury: Results of the WHO Collaborating Centre Task Force on Mild Traumatic Brain Injury. J Rehabil Med. 2004;43 (Suppl):28–60. [PubMed: 15083870]
Cuthbert J.P. et al. Epidemiology of adults receiving acute inpatient rehabilitation for a primary diagnosis of traumatic brain injury in the United States. J Head Trauma Rehabil. 2014;30(2):122–135. [PubMed: 24495917]
Langlois Orman J.A. Epidemiology. In. In: Silver J.M, McAllister T.W, Yudofsky S.C, editors. Textbook of Traumatic Brain Injury. 2nd. Washington, DC: American Psychiatric Publishing, Inc; 2011. p. xxii.
Jager T.E. et al. Traumatic brain injuries evaluated in U.S. emergency departments, 1992–1994. Acad Emerg Med. 2000;7(2):134–140. [PubMed: 10691071]
Andersson E.H. et al. Epidemiology of traumatic brain injury: A population based study in western Sweden. Acta Neurol Scand. 2003;107(4):256–259. [PubMed: 12675698]
Santos M.E, De Sousa L, Castro-Caldas A. Acta Med Port. 2003;16(2):71–76. [PubMed: 12828007]
Kraus J.F, Chu L.C. Epidemiology. In. In: Silver J.M, McCallister T.W, Yudofsky S.C, editors. Textbook of Traumatic Brain Injury. vol. 1. Washington, DC: American Psychiatric Publishing, Inc; 2005. pp. 3–26.
Kraus J.F. et al. Blood alcohol tests, prevalence of involvement, and outcomes following brain injury. Am J Public Health. 1989;79(3):294–299. [PMC free article: PMC1349550] [PubMed: 2916714]
Parry-Jones B.L, Vaughan F.L, Miles Cox W. Traumatic brain injury and substance misuse: A systematic review of prevalence and outcomes research (1994–2004). Neuropsychol Rehabil. 2006;16(5):537–560. [PubMed: 16952892]
Rimel R.W. A prospective study of patients with central nervous system trauma. J Neurosurg Nurs. 1981;13(3):132–141. [PubMed: 6912282]
Savola O, Niemela O, Hillbom M. Alcohol intake and the pattern of trauma in young adults and working aged people admitted after trauma. Alcohol Alcohol. 2005;40(4):269–273. [PubMed: 15870091]
Langlois J.A. et al. Traumatic brain injury-related hospital discharges. Results from a 14-state surveillance system, 1997 Morbidity and mortality weekly report. MMWR Surveill Summ. 2003;52(4):1–20. [PubMed: 12836629]
Guskiewicz K.M. et al. Association between recurrent concussion and late-life cognitive impairment in retired professional football players. Neurosurgery. 2005;57(4):719–726. discussion 719–726. [PubMed: 16239884]
Stein T.D, Alvarez V.E, McKee A.C. Chronic traumatic encephalopathy: A spectrum of neuropathological changes following repetitive brain trauma in athletes and military personnel. Alzheimers Res Ther. 2014;6(1):4. [PMC free article: PMC3979082] [PubMed: 24423082]
Karantzoulis S, Randolph C. Modern chronic traumatic encephalopathy in retired athletes: What is the evidence? Neuropsychol Rev. 2013;23(4):350–360. [PubMed: 24264648]
Guskiewicz K.M. et al. Cumulative effects associated with recurrent concussion in collegiate football players: The NCAA Concussion Study. JAMA. 2003;290(19):2549–2555. [PubMed: 14625331]
Annegers J.F. et al. The incidence, causes, and secular trends of head trauma in Olmsted County, Minnesota, 1935–1974. Neurology. 1980;30(9):912–919. [PubMed: 7191535]
Castile L. et al. The epidemiology of new versus recurrent sports concussions among high school athletes, 2005–2010. Br J Sports Med. 2012;46(8):603–610. [PubMed: 22144000]
Maas A.I, Stocchetti N, Bullock R. Moderate and severe traumatic brain injury in adults. Lancet Neurol. 2008;7(8):728–741. [PubMed: 18635021]
Thurman D.J, Branche C.M, Sniezek J.E. The epidemiology of sports-related traumatic brain injuries in the United States: Recent developments. J Head Trauma Rehabil. 1998;13(2):1–8. [PubMed: 9575252]
McCrea M. et al. Acute effects and recovery time following concussion in collegiate football players: The NCAA Concussion Study. JAMA. 2003;290(19):2556–2563. [PubMed: 14625332]
Schulz M.R. et al. Incidence and risk factors for concussion in high school athletes, North Carolina, 1996–1999. Am J Epidemiol. 2004;160(10):937–944. [PubMed: 15522850]
Bakhos L.L. et al. Emergency department visits for concussion in young child athletes. Pediatrics. 2010;126(3):e550–e556. [PubMed: 20805145]
Keenan H.T. et al. A population-based study of inflicted traumatic brain injury in young children. JAMA. 2003;290(5):621–626. [PubMed: 12902365]
Parks S. et al. Characteristics of non-fatal abusive head trauma among children in the USA, 2003–2008: Application of the CDC operational case definition to national hospital inpatient data. Inj Prev. 2012;18(6):392–398. [PMC free article: PMC4772141] [PubMed: 22328632]
Winqvist S. et al. Traumatic brain injuries in children and young adults: A birth cohort study from northern Finland. Neuroepidemiology. 2007;29(1–2):136–142. [PubMed: 17989501]
McKinlay A. et al. Prevalence of traumatic brain injury among children, adolescents and young adults: Prospective evidence from a birth cohort. Brain Inj. 2008;22(2):175–181. [PubMed: 18240046]
Anstey K.J. et al. A population survey found an association between self-reports of traumatic brain injury and increased psychiatric symptoms. J Clin Epidemiol. 2004;57(11):1202–1209. [PubMed: 15567638]
Silver J.M. et al. The association between head injuries and psychiatric disorders: Findings from the New Haven NIMH Epidemiologic Catchment Area Study. Brain Inj. 2001;15(11):935–945. [PubMed: 11689092]
Zaloshnja E. et al. Prevalence of long-term disability from traumatic brain injury in the civilian population of the United States, 2005. J Head Trauma Rehabil. 2008;23(6):394–400. [PubMed: 19033832]
Jennett B, Bond M. Assessment of outcome after severe brain damage. Lancet. 1975;1(7905):480–484. [PubMed: 46957]
Selassie A.W. et al. Incidence of long-term disability following traumatic brain injury hospitalization, United States, 2003. J Head Trauma Rehabil. 2008;23(2):123–131. [PubMed: 18362766]
Boake C. et al. Lost productive work time after mild to moderate traumatic brain injury with and without hospitalization. Neurosurgery. 2005;56(5):994–1003. discussion 994–1003. [PubMed: 15854247]
Finkelstein E, Corso P.S, Miller T.R. The Incidence and Economic Burden of Injuries in the United States. Oxford: Oxford University Press; 2006.
The Report to Congress on Mild Traumatic Brain Injury in the United States: Steps to Prevent a Serious Public Health problem. Atlanta, GA: 2003. National Center for Injury Prevention and Control. Retrieved from http://www​.cdc.gov/ncipc​/pub-res/mTBI/mTBIreport.pdf.
Hayward P. Traumatic brain injury: The signature of modern conflicts. Lancet Neurol. 2008;7(3):200–201. [PubMed: 18275921]
Iverson G.L. et al. Challenges associated with post-deployment screening for mild traumatic brain injury in military personnel. Clin Neuropsychol. 2009;23(8):1299–1314. [PubMed: 19882473]
Taylor B.C. et al. Prevalence and costs of co-occurring traumatic brain injury with and without psychiatric disturbance and pain among Afghanistan and Iraq War Veteran V.A. users. Med Care. 2012;50(4):342–346. [PubMed: 22228249]
Terrio H. et al. Traumatic brain injury screening: Preliminary findings in a US Army Brigade Combat Team. J Head Trauma Rehabil. 2009;24(1):14–23. [PubMed: 19158592]
Hoge C.W. et al. Mild traumatic brain injury in U.S. Soldiers returning from Iraq. N Engl J Med. 2008;358(5):453–463. [PubMed: 18234750]
Mac Donald C.L. et al. Detection of blast-related traumatic brain injury in U.S. military personnel. N Engl J Med. 2011;364(22):2091–2100. [PMC free article: PMC3146351] [PubMed: 21631321]
DePalma R.G. et al. Blast injuries. N Engl J Med. 2005;352(13):1335–1342. [PubMed: 15800229]
Sayer N.A. Traumatic brain injury and its neuropsychiatrie sequelae in war veterans. Annu Rev Med. 2012;63:405–419. [PubMed: 22248327]
Nakagawa A. et al. Mechanisms of primary blast-induced traumatic brain injury: Insights from shock-wave research. J Neurotrauma. 2011;28(6):1101–1119. [PubMed: 21332411]
Hicks R.R. et al. Neurological effects of blast injury. J Trauma. 2010;68(5):1257–1263. [PMC free article: PMC2958428] [PubMed: 20453776]
© 2016 by Taylor & Francis Group, LLC.
Bookshelf ID: NBK326730PMID: 26583186


  • PubReader
  • Print View
  • Cite this Page

Other titles in this collection

Related information

  • PMC
    PubMed Central citations
  • PubMed
    Links to PubMed

Similar articles in PubMed

See reviews...See all...

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...