Traumatic brain injury (tbi) is a leading cause of death and disability in the United States. It is estimated that 2.5 million cases of TBI occur annually, leading to over 2.2 million emergency department (ED) visits, 280,000 hospitalizations, and 52,000 deaths.^1,2 Per the Centers for Disease Control and Prevention (CDC), the total annual rate of TBI has increased from 521.0 per 100,000 persons in 2001 to 823.7 per 100,000 persons in 2010. At the same time, the mortality from TBI has decreased slightly from 18.5 per 100,000 persons in 2001 to 17.1 per 100,000 persons in 2010³ (Fig. 19–1). Currently, it is estimated that an overall 12.1% to 41% of adults have a history of TBI.^4–7

It is important to understand a distinction exists in the literature between TBI and concussion due to sports and recreation, despite concussions being a form of mild traumatic brain injury. Aware of this distinction, it is estimated that another 1.6 to 3.8 million mild TBIs or concussions occur annually due to sports and recreation-related injuries alone.⁸

In this chapter, we will summarize the epidemiology of traumatic brain injury, focusing on the incidence, prevalence, risk factors, causes of injury, and long-term impacts. The primary focus will be on cases of TBI that lead to medical attention in the emergency department or hospital. Additionally, separate sections will investigate the epidemiology of TBI in the military and sports populations.

Age

TBI occurs in persons of all ages, with those that are young and old at highest risk. In the United States, the rate of ED visits for TBI is highest in children under the age of 5 years old at an annual rate of 2193.8 per 100,000 persons in 2009 to 2010, with those between the ages of 15 and 24 years at a distant second at an annual rate of 888.7 per 100,000 persons.⁹ Hospitalizations are highest for those aged 65 years or older, at a rate of 294.0 per 100,000, and lowest for those under the age of 5 years old, indicating a difference of severity in the injury.⁹ In the Netherlands, the rate of TBI between 2010 and 2012 was highest in individuals 85 years old or older, at 578.2 per 100,000 person-years; patients between 75 and 84 years old had the next highest incidence, at 307.6 per 100,000 person-years.¹⁰

Gender

Overall, males are twice as likely to suffer from TBI than females.^4,5,11 This difference does not occur until middle childhood, with incidence of TBI being nearly equal in males and females under the age of 5 years.⁷ After that age, males are roughly 1.5 times more likely to suffer a traumatic brain injury until early adolescence, when they are 2.2 times more likely to suffer TBI than females.^12,13 The higher incidence of TBI persists in males throughout adulthood until roughly age 65, when the incidence of TBI is equal between the sexes^14–16 (Fig. 19–2).

Alcohol and Substance Use

More than half of TBI cases have been associated with alcohol consumption, and up to 30% of those who suffer TBI have a prior history of alcohol dependence.^17,18 Alcohol intake at time of injury is more commonly seen in male adults aged 34 to 54; injuries in this group are more commonly a result of suicide, assault, or fall.¹⁷ Those who suffer from fatal TBI are also more likely to have consumed alcohol than those with nonfatal injuries, and those who consumed alcohol at the time of their first head injury are more likely to suffer a second head injury throughout their lives.^17,19

A history of alcohol intoxication prior to age 14 or self-report of frequent alcohol consumption prior to age 14 has been shown to be predictive of TBI in adolescence and early adulthood.²⁰ Parental alcohol use has also been predictive of TBI in children, nearly doubling the risk of TBI children under the age of 14 years.¹³ Those with a history of substance use are more likely to suffer a TBI.¹⁸ Additionally, patients with a history of TBI have an increased risk for substance; this is attributed to poor coping strategies.^18,21

Social policy may affect the rate of TBI through changes to taxes on alcohol. In 2004, the alcohol tax decreased in the Netherlands by one-third, leading to a 25% increase in per capita alcohol consumption. As a result, the prevalence of alcohol use in moderate to severe TBIs increased by 11.2% between 1999 and 2007, but this was not a significant finding.¹⁷

Causes of Brain Injury

Falls have become the leading cause of TBI overall, accounting for 32% to 39% of all TBI-related ED visits, hospitalizations, and death, with a large portion of those cases occurring in elderly adults.^22,23 Over half the cases of TBI due to ground-level falls occur in persons aged 70 years old or older,²⁴ and between 44.3% and 82.9% of cases of TBI in the elderly occur as a result of falls.^2,14–16,25 Falls are also the most common cause of TBI in children, making up 27% to 67% of all causes of TBI^2,7,26–28 (Fig. 19–3).

Motor vehicle accidences are the second most common cause of TBI, comprising between 14.1% and 19% of TBI-related emergency department visits, hospitalizations, and deaths.^2,22,23 It is the most common cause of TBI in young adults, causing up to 64.4% of cases of TBI in those aged 18 to 44 years.²⁵

Being “struck by/against” was the next most common cause of TBI for those who sought medical attention in the ED or were hospitalized, with most of these injuries being related to sports and recreation.² This is the second most common cause of TBI in those under 15 years old, leading to one-quarter of injuries.² Finally, assault makes up 10% of the cases for TBI, with the highest rate in young adults.²

Disability

TBI is a leading cause of disability in the United States. In 2005, it was estimated that 3.17 million people in the United States were living with disability as a result of traumatic brain injury.²⁹ It is estimated that 43.3% of patients discharged from the hospital following a TBI will have long-term disability, with those who suffered self-inflicted gunshot wound being most likely to be disabled.³⁰ One study found that females were more likely to be disabled than males; however, this may be due to differences in mechanism of injury.³⁰ In the Netherlands, it is estimated that TBI causes an average of 7.07 disability adjusted life-years per patient and a total of nearly 53,000 years of life with disability nationally.¹⁰

Psychiatric Disorders

Patients who suffer traumatic brain injury have a high prevalence of psychiatric disorders, both prior to and following TBI. Prior to injury, over half of patients have a psychiatric disorder, with the most common cause being substance use.¹⁸ Following injury, the most common psychiatric disorders are major depressive disorder (45%), anxiety (38%), and substance use disorder (21%).¹⁸ Over 70% of people suffering from anxiety or major depressive disorder did not have a prior history of either condition.¹⁸

Psychiatric disorders can develop long after the initial injury.^31,32 One study found that males who suffered TBI in childhood or adolescence were more than twice as likely to develop a psychiatric disorder as an adult.³² Children who were admitted to the hospital for TBI by the age of 5 years old were more likely to develop oppositional defiant disorder, conduct disorder, attention deficit hyperactivity disorder, or substance use disorder in late childhood and adolescence.^33,34 No increase in psychiatric disorders was seen in children who were treated for TBI as an outpatient, suggesting that severity of injury plays a role.³³ The presence of depression following TBI has been associated with poor functional outcomes, decreased social reintegration, and increased rate of suicide.^21,35

Mortality

Unintentional injuries are the leading cause of death in the United States for persons between the ages of 1 and 44 years old, and TBI results in more than 50,000 deaths per year in the United States.^2,36,37 The presence of TBI as part of the injury complex in patients with unintentional injuries significantly increases the mortality rate. In one study, the presence of TBI tripled the likelihood of death in the emergency department in those presenting with motorcycle collisions.³⁸ In that same study, 7.6% of those who suffered from TBI died compared with 1.1% of those without TBI.³⁸ Firearms accounted for slightly over one-third of the cases of TBI-related mortality, with the majority being due to suicide. The rate of firearm-related TBI deaths was 11.2 per 100,000 males between the years 1997 and 2007, which was six times the rate of females.

Motor vehicle collisions were the next most common cause of TBI-related death, accounting for 31.4% of deaths. Again, the rate was higher in males than females, with 8.2 per 100,000 males and 3.5 per 100,000 females. The rate of death has decreased by 45.5% among vehicle occupants and 32.8% among pedestrians struck by cars between 1997 and 2007, but the rate has increased by 133.1% in motorcycle riders during that same time period.^37,38

Due to advances in medical care after traumatic brain injury, mortality directly due to injury has consistently decreased, from 19.3 per 100,000 population in 1997 to 17.1 per 100,000 population in 2010. However, those who survive the initial injury continue to have higher rates of mortality.^3,35,37 Patients who survived initial hospitalization for TBI have a 2.25 to 2.5 increased rate of death compared with the general population, a number that decreases to 1.5 to 1.71 for those surviving the first year after injury.^35,39,40 For those who require at least moderate assistance in care, the risk of death is 13.2 times higher than the general population.⁴¹ This leads to a decreased life expectancy of 4 to 6 years per person.^35,40

Fall-related TBI is a significant cause of mortality in the elderly. The rate of death is highest in those aged 85 years and older, at 103.8 per 100,000 population, followed by those 75 to 84 years old, at 51.4 per 100,000, and those aged 65 to 74 years old, at 24.5 per 100,000 population.³⁷ Multiple studies have identified older age at time of injury as significant predictor for mortality. However, when compared with the general population, those who suffered a TBI at age 85 years old and older did not have an increase in mortality after injury.^{14,23,35,39,40} This is likely due to the high mortality in that age group.

Those aged 15 to 19 years old and 35 to 44 years old had the highest increase in mortality, at 4.78 and 3.80 times the general population, respectively.³⁹ Other factors that increase mortality include male sex, being in a vegetative state, having other impairments of mobility or feeding as a result of the injury, lower education or socioeconomic level, use of alcohol at time of injury, and living in a nonurban area.^{12,17,35,39,40,42}

Cause of death following traumatic brain injury varies based on the age of the patient. For those under the age of 35 years old, external causes of death, namely unintentional injuries or homicide, remain the leading cause of death.³⁹ Mortality from pneumonia, including aspiration pneumonia, seizures, cardiovascular disease, sepsis, and digestive disorders were significantly elevated in patients with TBI as compared with the general population.^35,40,41

Societal Costs

Total costs following traumatic brain injury are high and growing. Based on 2013 dollars, annual total costs are estimated between $62.2 and 78.1 billion dollars, with $13.1 billion due to direct costs following injury.⁴³ One study found that the cost for hospitalization after motorcycle accident averages $20,000 more if the patient suffers traumatic brain injury than without traumatic injury.³⁸ In 2000, the estimated total cost for all TBI-related hospitalizations in children 17 years old or younger was greater than $1 billion, making it the fifth most expensive hospital diagnosis.⁴⁴ Medical costs continue after the initial elevation. One study of Medicaid and commercial insurance databases found an increased cost of nearly $50,000 per child over the first 4 years after abusive head trauma in children aged 4 years old or younger.⁴⁵

Indirect costs make up a large portion of total cost after traumatic brain injury, and lost wages make up a significant proportion of overall cost for TBI. In one study, 10.4% of those with TBI saw their personal income drop below $10,000 per year one year after injury, with another 6.1% of those who made between $25,000 and $50,000 per year seeing a loss in income.⁴⁶ Another study noted that mean monthly income dropped 51% between the time prior to injury to one year following injury, with an estimated national lost income of over $600 million and lost income taxes of nearly $100 million one year after injury.⁴⁷ To make up for lost income, family support rose by 10% and public assistance rose 275% between time of injury and one year following injury.⁴⁷

High costs following TBI are seen in other nations as well. Looking at population-based studies, the overall cost has been estimated to be as high as $101.4 million per year in New Zealand and $433.8 million per year in the Netherlands, using U.S. dollars.^10,48 In New Zealand, the total first-year costs for all new traumatic brain injuries has been estimated to be $47.9 million, averaging to be $4,123 per person, of which $3,783 was due to direct health care costs.⁴⁸ The cost per person was higher in those suffering moderate and severe injuries due to higher initial hospital costs, but mild TBI had higher overall cost due to higher prevalence of the injury.⁴⁸

Return to Work

Between 31.1% and 84% of patients were employed prior to traumatic brain injury, with most being employed as technicians, trade workers, or manual laborers.^47,49–55 Unemployment after TBI is higher than that of the general population.^50,54 Most people who regain employment do so within the first 6 months to one year following injury, with little increase in employment rate following that time.^52,56 One year following injury, only 26.1% to 72% of people are employed, and there is a decrease in stable, full-time employment in those who return to the workforce.^{46,47,53–55,57–61} In one study, roughly 35% of those who regained employment at 2 years following injury were employed part-time.⁵⁰ In another study, only 36.5% of people reported working the same number of hours prior to the injury at a one-year follow-up, with 12.9% of people reporting that they were still employed but worked fewer hours than prior to injury.⁶² Furthermore, there is a decrease in the maintenance of employment, with less than half of those in the workforce being able to maintain employment over a 3-year follow-up period.⁵⁴ Another study found that 22% of people who had regained employment at 6 months following injury were unemployed 2 years after injury.⁵¹

Patients who are employed prior to injury are significantly more likely to be employed following injury.^{47,49–51,53,63,64} In two studies, none of those who were unemployed prior to the injury were employed at 6 months or one year follow-up.^47,51 Racial differences exist in both preinjury and postinjury employment, with Caucasians being more likely to be employed at both time points than minorities.^49,50,63,65 Caucasians have also been found to have more employment stability after TBI than minorities.⁶³

Severity of injury also plays a role in return to employment after TBI. Those with longer duration of coma and post-traumatic amnesia, longer length of stay in the acute hospital and inpatient rehabilitation facility, and those with concurrent limb injuries⁵³ were less likely to be employed^{53,55,57,59,60,64} One study has identified that a higher score on the Glasgow Coma Scale (GCS) at admission has been a positive predictor of postinjury employment; however, this has not been consistent in the literature.^57,59 Level of physical disability also plays a role, as those with greater mobility are more likely to be employed.^{54,55,57,63,64} Likewise, those with greater cognitive disability or psychiatric comorbidities were more likely to be unemployed.^{51–54,57,58,60,61,66,67} Positive predictive factors for employment after TBI also include younger age,^{51,53,55,59,63,64,68,69} higher level of education,^{49,55,60,62–65} being married,^49,50,55,65 driving,⁵⁴ being discharged to home after inpatient rehabilitation stay,⁶¹ and working as a professional at time of injury.^54,55

Homelessness

The prevalence of TBI is higher in persons who are homeless. In a study of homeless patients living in Toronto, Canada, the overall lifetime prevalence of TBI was 53%, with 58% of men and 42% of women having suffered a TBI.⁷⁰ A similar study in Leeds, the United Kingdom, found a lifetime prevalence of 48% in the homeless population, which was much higher than the lifetime prevalence of 21% in matched controls.⁷¹ The majority of brain injuries were suffered prior to the onset of being homeless, with 70% to 90% of people reporting the first TBI occurring prior to becoming homeless.^70,71 Those who were homeless and had a history of TBI reported poorer health, particularly an increased rate of seizures and mental health disorders, as well as alcohol and substance use disorders.⁷⁰

Incarceration

Overall, the estimates for lifetime prevalence of TBI in the incarcerated population are higher than the general population, with 22.6% to 87.0% of incarcerated adults^72–84 and 18.3% to 72.1% of youths in juvenile detention centers^85–89 reporting a prior TBI. Of these individuals, 71% to 92% suffered a mild injury^84,88 and 13% to 56.7% reported multiple TBIs.^72,88 Those who are incarcerated or living in residential facilities after release from prison reported a high prevalence of recent TBI, with 22% suffering one within the past 6 months⁹⁰ and 36.2% within the past 12 months.⁸⁴ Unlike general population, where a higher prevalence of TBI is seen in males, the prevalence of TBI in males and females is roughly equal in those who are incarcerated.^77,83,87

It is unclear whether a history of TBI increases risk for participating in criminal behaviors. One study found that 80% of those with a history of TBI suffered it prior to the initial encounter with the law.⁸² Another study found that males who suffered TBI in childhood or adolescence were 1.6 times more likely to become a criminal offender as an adult than those without TBI.³² Those with TBI exhibited more anger and aggressive behavior and physical altercations,^79,84,88 as well as a history of prior incarceration.⁸¹ Two studies in the adult population found that those with a history of TBI were more likely to commit violent crimes than those without history of TBI^73,91; however, this association was not seen in juveniles.⁸⁵

Elderly

In the United States, admission rates to Level I and II trauma centers is highest for those over the age of 85 years, with an estimated 152 admissions for every 100,000 of the population.¹⁴ Individuals aged 75 to 84 years old were found to have the second highest incidence, with 94 admissions per 100,000 population.¹⁴ Between 2007 and 2010, there was an increase of 25% for persons aged 85 years old and older and 20% for those aged 75 to 85 years old.¹⁴ In the Netherlands, those aged 85 years old and older has also been found to have the highest incidence of TBI, with those aged 75 to 84 years old having the next highest incidence at 578.2 per 100,000 person-years and 307.6 per 100,000 person-years, respectively. The rate in the elderly population is significantly higher than the young adult population (271.6 per 100,000 person-years).¹⁰

Unlike the predominance of men suffering from traumatic brain injury in the younger population, in the older population, there is nearly an equal incidence of traumatic brain injury between men and women.^14–16,68 Falls are the most common cause of TBI, making up between 44.3% and 92% of the cases of TBI in the elderly.^{14–16,25,68} Motor vehicle collisions and being hit by a vehicle as a pedestrian are the next most common causes.^15,16 Due to the lower intensity of required force to induce injury, older adults are more likely to have less severe injuries based on GCS at admission and injury severity score (ISS) than younger patients; however, these patients suffer worse outcomes.¹⁶ In-hospital mortality is higher for those over the age of 65 years, and mortality rates increase with severity of injury.^15,16,24,92 Older patients have increased length of stay in inpatient rehabilitation, leading to significant added cost.^25,93 Functional status at both admission and discharge from inpatient rehabilitation is lower for elderly persons than young adults, and deficits can persist at least 5 years following injury⁹⁴, and these people are more likely to be discharged to an extended care facility^{16,25, 68,69,93} This is due, in part, to the higher rate of medical comorbidities and use of certain medications prior to injury.

Military

TBI has been called the signature injury from the combat in Iraq and Afghanistan, with most cases being mild injuries.^95,96 Actual prevalence of TBI has been difficult to determine based on postdeployment symptom questionnaires.^95,97 Rate of TBI in service men and women during deployment has ranged from 5.2% to 23% based on the type of assessment used.^98–105 Rate of TBI varied based on position in the military. Those in the U.S. Marine Corps and Army are more likely to suffer TBI than those in the Air Force or Navy, and enlisted officers are more likely to be injured than officers.^101,106,107 One study also identified that paratroopers were more likely to suffer mild TBI than general soldiers.¹⁰² As with nonmilitary persons, males are at increased risk for suffering TBI than females, with 82% to 97% of mild cases occurring in men.^106,108 For more severe injuries, men comprised 97% of the population who were hospitalized with TBI but only made up 90% of military personnel.¹⁰⁷ In males soldiers, the incidence of TBI increased from 65.1 per 100,000 soldiers in the year 2000 to 139.4 per 100,000 soldiers in 2006; in contrast the incidence in females soldiers remained stable at 36.8 per 100,000 soldiers during the same period.⁹⁶ The majority of cases of TBI occur due to combat.^107,109 Blasts are the most common cause of injury, accounting for 48.8% to 74.3% of cases of TBI in the military.^{100,107,108,110} Improvised explosive devices (IEDs) cause 41.3% to 52.2% of these injuries.^109,110 Gunshot wounds are the second most common cause of TBI, leading to 8.7% to 17.7% of TBI.^109,110

TBI can cause long-term consequences to the health of military personnel. In one study of military personnel who suffered blast injuries, those with TBI were five times more likely to report major negative changes in health than those without TBI.¹¹¹ Mental health disorders increased after TBI, and these were higher in those with moderate to severe injuries.¹¹⁰ Overall, those with TBI had increased rates of depression, anxiety, and post-traumatic stress disorder (PTSD), and suffering a TBI during deployment was the strongest predictor for development of PTSD after deployment.^95,104,105 The prevalence of PTSD in those suffering blast-related TBI was 61%, compared with only 28% of those who had medical evacuation from the battlefield without TBI.¹¹² An association between abnormal diffusion tensor imaging (DTI) and development of PTSD has been found, suggesting a physiological link between injury to the brain and PTSD.¹¹³ Substance use increases after TBI, with dependence on alcohol, nicotine, and illicit drugs being highest within the first 30 days after injury.¹⁰⁶

Persons with TBI due to combat have increased rates of physical disability than those with other combat-related injuries. One study found that 87% of those with blast-related TBI suffered from moderate to severe overall disability compared with 61% of those with combat-related injuries that did not include TBI.¹¹² Another study identified that those with TBI were nearly four times more likely to be medically retired than those with other combat-related injuries.¹¹⁴

Sports-Related Concussion

Mild TBI, or concussion, has garnered significant attention in the national media and poses a threat to the health of youth athletes. Seven percent of sports and recreation injuries suffered between 2001 and 2012 resulted in TBI, and rates of TBI have been increasing in all age groups, with an overall annual rate of increase of 15.5%.^115,116 Rates of TBI vary based on the sport played, with an overall incidence of 0.24 to 0.36 TBIs per 1,000 athletic exposures.^116,117 In American high school and collegiate sports, boys’ football and girls’ soccer are the most common causes of sports-related TBI, with an estimated incidence of 0.35 to 3.74 concussions per 1,000 athletic exposures, with college athletes having a higher rate of concussion than youth or high school athletes.^{116,118–125} Male baseball players have the lowest rate of concussion, at 0.14 concussions per 1,000 athletic exposures.¹²⁵

Concussions in professional sports leagues have led to significant loss of playing time and, in some cases, shortening of careers. In a study of the National Hockey League (NHL) players, the head was identified as the most commonly injured body part, making up 16.8% of all injuries and 16.7% of games lost.¹²⁶ Using the Major League Baseball (MLB) injury tracking database, the rate of concussion in the major and minor leagues was identified as 0.42 per 1,000 athletic exposures and was found to be 1.8 times higher in the minor league than major league.¹²⁷ Nearly 13% of all Ultimate Fighting Championship (UFC) mixed martial arts events ended in knockout, with another 21.2% ending in technical knockout where the match was stopped because the athlete was unable to defend himself or herself after hits to the head, which corresponds to an overall rate of 15.9 TBIs per 100 athletic exposures, which is higher than the rate seen in other professional sports.¹²⁸

Multiple risk factors have been identified for sports-related concussion. Overall, females are more likely to suffer a sports-related concussion than males when comparing sports played by both males and females, such as soccer or basketball, and those with a prior concussion are more than twice as likely to suffer a concussion as those without a history of concussion.^{116,125,129–135} Multiple studies have researched the impact of age on risk of concussion, with both older and younger age being identified as risk factors for sports-related concussion.^118,130,134 More athletes are injured during gameplay than during practice.^119–124 Within individual sports, certain positions and plays may be associated with increased rate of sports-related concussion. In soccer, heading the ball is the most common cause of concussion, causing 30.5% of concussions; goal-tending is the next most common cause of injury, accounting for 11.9% of injuries.¹²³ In football, over 70% of concussions due to player collision occurred with head-to-head contact, with hits involving the front or side of the head being most likely to cause concussion.¹¹⁹ Injuries due to contact with the top of the head were the least frequent, and many of these occurred with poor tackling form, such as initiating contact with a “head-down” position. As a result, athletes are recommended to tackle with the head up to prevent unnecessary contact.¹¹⁹ In baseball, most injuries occurred during batting, fielding, or running, with almost half of the injuries occurring at home plate.¹²⁷ Catchers are at highest risk for suffering concussion during baseball games.¹²⁷ In a study of youth hockey players in Canada, those in the Pee Wee leagues, aged 11 to 12 years old, that allowed body checking had a greater than three times higher rate of overall concussion and severe concussion, which was defined as a concussion that led to more than 10 days lost from play.^132,133 There was no difference in concussion rate in these athletes once they reached the Bantam leagues, in which body checking was allowed in all leagues.¹³⁶ One study identified that hockey goalies were at decreased risk for concussion than forwards, but another study did not find a difference in rate of concussion based on position.^132,133 There was no difference in rate of concussion in youth hockey players based on the player size, level of play, team win-loss record, team penalty minutes per game, and player year of play.^132,133 Other risk factors identified include increased number of games during the season or years of play, decreased number of hours of training per week, increased impulsivity, and presence of preseason headache or neck pain.^131,134,137

Insufficient recognition and reporting of symptoms of concussion by athletes has been a barrier to prevention and treatment. A study of collegiate athletes found that only 12.4% to 13.5% of soccer athletes and 6.8% to 16.5% of male football athletes reported a diagnosis of concussion in the prior year despite 46.2% to 62.7% of soccer and 34.1% to 70.4% of football athletes reporting symptoms of a concussion after a hit to the head on a single questionnaire.^129,130 In a similar study of Canadian Football League (CFL) players, only 8.4% of players reported a diagnosis of concussion, but 44.8% reported symptoms of concussion in the prior year.¹³¹ Athlete attitudes toward concussion have posed another barrier to management of sports-related concussion. In a study of youth hockey players in Canada, 95% of players reported that they knew they should stop playing if they had a concussion, but only 42.9% of those who suffered a concussion did stop playing at the time of injury.¹³⁸ Most players reported that they wanted to continue to play, while others reported not wanting to let down the team, coach, parents, or peers as reasons for not reporting the injury.¹³⁸

Legislation has been passed to increase awareness and player safety. In 2009, Washington State enacted the Lystedt Law, which required education regarding concussion for coaches, parents, and athletes. Additionally, this law mandated the immediate removal of the athlete from play if concussion was suspected, and clearance of the athlete by a health care professional trained in management of concussion prior to return to play. The remaining 49 states and Washington, D.C., passed similar legislation by 2014. Rate of TBI in high school athletes in Washington State roughly doubled between the 2008–2009 and 2010–2011 seasons, likely the result of increased awareness of concussions.¹¹⁷ When comparing states that had enacted legislation by the 2011–2012 season to those without legislation, there was a 10% increase in rate of treated concussion for children aged 12 to 18 years in states with legislation.¹³⁹ In 2012, 98.9% of boys’ football and boys’ and girls’ soccer coaches reported completing concussion education, with 74.4% reporting that it was mandatory prior to beginning coaching.¹⁴⁰ More than 80% of coaches reported that both the athletes and parents signed concussion information forms, but only 59.1% of football coaches and 39.4% of soccer coaches reported talking with their athletes about concussion.¹⁴⁰ Despite the education, one study found that 40% of athletes who suffered concussion reported that their coach was unaware of the injury when surveyed 3 years after passage of the Lystedt Act.¹²⁴ Another study found that the number of days out of athletic events increased by 2.35 to 6.19 days in females, but no statistically significant increase was seen in male athletes.¹¹⁷

Traumatic brain injury poses a significant public health concern due to the high rate of disability that occurs as a result of the injury. There is emerging evidence that TBI may be associated with the development of neurodegenerative diseases such as chronic traumatic encephalopathy (CTE), amyotrophic lateral sclerosis (ALS), and Parkinson’s disease, further highlighting the need for prevention advocacy and education.¹⁴¹