In its most recent report on TBI in the United States spanning the years 2002–2006, the CDC reported that an estimated 1,691,481 people (576.8 per 1,000,000) sustain a TBI annually [32]. Of this number, 1,364,797 (465.4 per 100,000), or nearly 80 %, are treated in the emergency department (ED) and released. 275,146 (93.8 per 100,000) individuals sustaining a TBI are hospitalized annually. It is further estimated that 51,538 (17.6 per 100,000) individuals sustaining a TBI annually die, and that TBI is a contributing factor in a third (30.5 %) of all injury-related deaths. These mortality rates are highly consistent with estimates in a separate report from the CDC spanning the years 1997–2007 [1], which report an annual average death rate from TBI of 53,014. Comparison of rates over time revealed increases in the incidence of TBI-related ED visits and hospitalizations [32, 33] particularly in children and older adults [32]. These increases were likely related to increases in the population over that time period and increases in falls, but may also represent an increased public awareness of TBI. TBI-related deaths decreased as much as 8.2 % over time [1, 32, 33], which may be related to increased preventive measures such as seat belt and helmet use [34, 35] and better overall treatment for severe TBI [36]. Incidence of new-onset disability from TBI annually has been estimated to be 80,000–90,000 new cases annually [37]. A more recent projected estimate indicated that incidence of new onset disability may actually be higher, at the rate of over 124,626 new cases per year or 43.3 % of all hospitalized TBI survivors [38].

Incidence rates of TBI vary widely across studies due to methodological differences. A review by Kraus and Chu [39] demonstrated that the incidence of TBI ranged from 92 cases per 100,000 persons to 618 per 100,000, with an average rate of fatal plus nonfatal hospitalized brain injuries estimated at 150 per 100,000 persons per year. Populations sampled from and case definitions of TBI differ across studies leading to variability in results. For instance, a recent study by Leibson et al. [40] found higher incidence rates (558 per 100,000) using record-review criteria to determine TBI, compared with incidence rates determined by CDC criteria (341 per 100,000). This study demonstrated that the CDC approach may significantly underestimate the true incidence of TBI, as it only included 40 % of cases identified by record review. Although 75 % of these missing cases presented to the emergency department, they were missing the necessary CDC-specified code to be counted as a TBI. Of these, 66 % were symptomatic for TBI.

Due to difficulties with consistent data coding across available databases, the newest incidence rates from the CDC did not address injury severity. However, earlier CDC estimates from the year 2000 documented that, of patients hospitalized due to TBI, over 50 % had mild injuries, 21 % had moderate injuries and 19 % had severe injuries, resulting in approximately 102,500 moderate and severe TBIs per year [41]. These rates do not include patients who died prior to hospitalization. More recently, a Congressional report from the CDC Working Group on mTBI in 2003 estimated that mTBI makes up 75 % of the TBIs in the United States each year [6].

Overall incidence rates of TBI reported by the CDC likely underestimate the true incidence of TBI, and even more so the rates of mTBI, given that these estimates do not include individuals either treated in outpatient settings or who do not present for treatment at all [1]. Estimates suggest that up to one fourth of all persons who sustain a TBI do not seek medical care [42]. It is also possible that individuals may be treated and discharged in the ER without adequate appreciation and documentation of a mTBI injury that occurred in conjunction with other more life-threatening injuries. This possibility is illustrated in a study by Powell and colleagues [43] that found 56 % of individuals prospectively identified to have a mTBI using a brief scripted interview and medical chart review did not have a mTBI diagnosis in their medical record and would have been missed by retrospective medical record review. Additionally, the most recent CDC data do not include military personnel who sustained a TBI abroad or who received care for TBI in federal, military, or Veteran Administration hospitals [32]. Given the high impact of TBI in the military, the epidemiology of TBI in military populations will be presented and discussed in detail later in this chapter. Individuals who sustain injuries as a result of sports accidents often experience injuries on the milder end of the spectrum and are most often treated in outpatient settings or do not seek medical treatment at all due to rapidly recovering symptoms. Because these individuals are typically not well-represented in hospital-based studies of incidence, TBI due to sports-related accidents will also be presented and discussed separately.

The leading causes of TBI in the US civilian population are falls (35.2 %) followed by motor vehicle-related injuries (17.3 %), a strike or blow to the head from or against objects (16.5 %), assaults (10 %), and other or unknown causes (21 %) [32]. Falls are the most common cause of TBI with an estimated number of 595,095 fall-related TBIs annually. Fall-related TBIs are greatest at the extremes of the life span, with the highest rates seen in children less than four and in adults over 75 years of age. In contrast, motor vehicle-related injuries are the leading cause of TBIs in late adolescence (ages 15–19) and early adulthood (ages 20–24). Assault-related TBIs are also highly represented in the 20–24 year age group [32, 33, 44]. See Fig. 1 for changes in rates of injury mechanism across age. Death from TBI is most commonly a result of firearms (34.8 %) particularly in the age ranges of 15–34 and > 75 years, followed by motor-vehicle accidents (31.4 %) particularly in the age range of 15–24 years, and falls (16.7 %) particularly in the age group >75 years [1]. TBIs associated with falls (58.4 %) and firearm injuries (49.9 %) are most likely to be associated with long-term disability [38].

Although a brain injury can happen to anyone, some groups are at higher risk than others. Age is an important mediating factor with regard to TBI incidence, with the highest rates of TBI occurring in children under 4 years of age, in adolescents between the ages of 15 and 19, and in adults over 65 [32]. Almost half a million emergency department visits for TBI are made annually by children 14 years of age and younger. On the other end of the life span, adults 75 years and older have the highest rates of TBI-related hospitalization and death. While rates of TBI deaths have been decreasing in younger persons (0–44 years), they have increased significantly in persons ≥75 years [1]. See Fig. 2 for age trends in estimated annual TBI rates. There is also evidence that elderly individuals are at risk for worse outcome from TBI than younger individuals [45, 46] and probability of long-term disability as a result of TBI has been shown to increase with age [38]. When injury mechanism is considered, children and older adults are at highest risk for fall-related TBIs, and adolescents and young adults are at highest risk for TBIs as a result of motor vehicle accidents [32].

Sex also represents a risk factor for TBI, with studies universally reporting higher rates of TBI in males than in females [32, 37, 42] at a ratio of approximately 1.6–2.8 [39]. Males account for approximately 59 % of all TBI cases in the United States and have higher rates of TBI than females in all age groups. The highest rates for all TBI-related emergency department visits, hospitalizations, and deaths combined are seen for males younger than 4 years of age [32]. Rates of injury peak in both males and females at both ends of the lifespan and in the adolescence. Although males continue to outnumber females, injury rates were most similar between males and females for the very young and at the later end of the age range when the most common mechanism of injury was falls. Likewise, both males and females, with males outnumbering females, showed increased rates of injury between the ages of 15–19 years of age, when most TBIs are due to motor vehicle accidents [32]. See Fig. 3 for rates of TBI ED visits in males and females across the lifespan. Higher rates of TBI in males may be explained by men being more frequently exposed to high-risk situations and motor vehicle accidents than women. Although probability of long-term disability following TBI was significantly higher for females (49.5 % compared to 39.9 %) [38], death rates from TBI are reported to be three times higher among males [1]. Additionally, firearm-related TBI suicides were higher among males than females for all race/ethnic and age groups [1].

Risk for TBI appears to be mediated by socioeconomic status and racial/ethnic group. Studies document that average annual numbers of TBIs tend to be higher in families at the lowest income levels [42, 47, 48]. Minority racial/ethnic groups have been shown to sustain higher rates of TBI [49, 50] and appear to be at higher risk for death following TBI [1]. For both sexes, American Indian/Alaska Natives (AI/AN) showed the highest annual average TBI-related death rates. The second-highest annual average rates of TBI-related deaths were seen in Blacks, and specifically in Black men. In contrast, Hispanics had the lowest rates of TBI deaths overall for both men and women [1]. When mechanism of injury was considered, rates of firearm-related suicides were particularly high among AI/AN men aged 15–34 and among White men aged ≥65 years. Rates of firearm-related TBI homicides were also highest among Blacks between the ages of 15 and 34 [1]. AI/AN showed the highest annual average rate of motor vehicle-related TBI deaths and fall-related deaths followed by Whites in both categories. A separate surveillance study spanning the year 1997 reported that Black and AI/AN men had the highest rates of TBI attributable to assault, at approximately four times the rates of White men [51]. In addition to being overrepresented in incidence of TBI, minority racial/ethnic groups have also been reported to have poorer overall psychosocial and functional outcome following TBI when compared with the majority group [52, 53].

Additional risk factors for TBI are history of alcohol/substance use and history of prior TBIs. Specifically, alcohol consumption has been indicated as a potential risk factor for brain injury, with positive associations seen between blood alcohol concentration (BAC) and risk of injury [54, 55]. In a 14-state CDC TBI surveillance system, it was found that among those with TBI due to motor vehicle incidents, 21 % had documented alcohol use of any level and 12 % had BACs above the legal limit for intoxication. Among those with TBI due to assault, 41 % had documented alcohol use of any level and 23 % had BACs above the legal limit [51]. Prior brain injury poses a separate risk for TBI [56]. The risk of a second TBI for those with past injuries is approximately 2.8–3.0 times that of the general non-injured population with rates for a third injury given two prior injuries increasing to 7.8–9.3 times above the general population [57]. A more recent study reported that 7 % of individuals hospitalized with a TBI had at least one recurrent TBI during the follow-up period [58].

TBIs related to sports and recreation activities are receiving more attention resulting in better monitoring and detection. These injuries are most often mild in nature and are frequently referred to as sports-related concussion in the literature. Though mild in nature, these injuries are often graded by severity according to existing guidelines [59, 60]. Grading systems reflect increasing severity of acute symptoms and alteration of consciousness with Grade I injuries reflecting brief symptom duration, short periods of confusion, and no LOC; Grade II injuries involving brief symptom duration, longer periods of confusion, and very brief or no LOC; and Grade III injuries representing longer duration of symptoms, long periods of confusion, and sustained periods of LOC (greater than 5 min). In recent years, consensus bodies endorsed individualized assessment of concussion severity, determined by measures of symptom recovery, rather than prospective grading of injury according to acute characteristics [61, 62]. Often the term concussion is preferred over mTBI because it is more commonly associated with expectations of transient symptoms and positive recovery [63]. The terms concussion and mTBI are synonymous and will be used interchangeably for the purposes of this chapter.

It is estimated that approximately 300,000 sports-related injuries with LOC occur each year [64]. Estimates rise to between 1.6 and 3.8 million per year when milder injuries without LOC and non-medically treated injuries are considered [33]. When taking into account both organized sports and recreational activities in younger populations, a recent analysis of data from the National Electronic Injury Surveillance System documented 173,285 individuals that were less than 19 years of age were assessed and treated in the emergency department for nonfatal TBI from 2001 to 2009 [65]. This represented 6.5 % of all sports and recreation-related emergency department visits in this age group. Over the study period, the estimated number of TBIs that presented to the emergency department increased by 62 %, with the rate of visits increasing 57 % from 190 per 100,000 persons to 298 per 100,000 [65]. Of interest, though the number of visits increased over the time period, the resultant rate of hospitalizations for TBI did not increase. Activities highly represented in the sample of injuries were bicycling, football, playground activities, basketball, and soccer. Activities with the greatest proportion of TBI injuries were, in order of risk, horseback riding (15.3 %), ice skating (11.4 %), golfing (11.0 %), all-terrain vehicle riding (10.6 %), and tobogganing/sledding (10.2 %). TBI in younger children was more highly associated with playground activities or bicycling. TBI in older children (10–19 years of age) was more likely to be associated with organized sports (football for boys; soccer or basketball for girls) or bicycling. Though rates of TBI increased over time, the authors of the study concluded that this was likely due to heightened awareness of TBI in sports and recreation, rather than increased risk or increased rates of participation in recreation or sports.

Recent prospective studies of organized sports at the high school level cite a concussion incidence level of 0.24 per 1,000 athlete exposures [66]. Athlete exposure is defined as one athlete participating in one practice or competition during which he or she is exposed to a possible athletic injury. Overall prevalence of concussive injury as a percentage of total athletic injuries at the high school level is estimated to be 9 % [33]. Concussions at the high school level occur at a higher rate during competitive play than during practice [67]. Specific sports are notable for having a higher risk for concussive injury including football, girls soccer, girls basketball, rugby, ice hockey, and lacrosse [67]. The primary cause of concussion in high school sports is contact with another player, followed by contact with the playing surface or equipment, followed by falls [66–69]. Though football represents the highest rate of injury (40.5 %) of all concussions at the high school level, studies including sports played by both sexes show that women athletes sustain a higher rate of concussions [66, 69]. In high school athletes, headache is the most prominent reported symptom (93.4 %) with amnesia noted in almost a quarter of reported concussions [70]. Gender differences have been noted in symptom presentation with male athletes reporting higher rates of confusion and amnesia and female athletes reporting drowsiness and sensitivity to noise [68, 70]. Of athletes that suffered a concussion during the reporting period, approximately 20 % had suffered a previous concussion [69]. Concussions represent a greater proportion of sports related injuries at the high school level but happen at a lower rate overall compared with collegiate sports.

Athletes at the high school level are now assessed and monitored by surveillance programs at a higher rate than in previous years [71]. Despite this heightened surveillance, return to play decisions are generally premature compared with available guidelines [60, 72]. A recent study found that male athletes were more likely to return to play 1–2 days after sustaining a grade II concussive injury (12.6 % vs. 5.9 %) and were more likely to return less than 1 day after a grade I injury (22 % vs. 0 %). Though it is not clear from the data why men return more quickly than women to competition or practice, there was no suggestion in the data presented that it was due to more severe injury in female athletes. This trend may reflect a more cautious management of female athletes [71].

There have been reports of death due to blunt trauma to the head in youth sports, but these events were rare [73]. Of 261 youth athletes whose deaths resulted from bodily trauma and vital organ damage during sports participation taken from a 30 year retrospective study, 12 deaths were due to boxing, 10 were due to helmet-to-helmet blows in football, and 16 were due to head trauma in baseball. One hundred and thirty-eight football players were reported to have died secondary to a subdural hematoma during the study period. Of note, 12 % of those players had a previous concussion a few days to 4 weeks prior.

In collegiate sports, TBI trends are similar to high school with a slightly higher rate of injury overall. Football continues to have the highest rate of concussion in collegiate sports with a rate of 11.1 injuries per 1,000 athlete exposures [74]. Injuries were more likely during a game. Similar to the high school data, injuries were most likely to occur from helmet to helmet contact. Men’s collegiate hockey has a fairly high rate of practice (5.3 %) and game-related (9 %) concussive injuries, with most concussions resulting from player contact (60.2 %) or from contact with the boards (26.3 %) [75]. Soccer at the college level demonstrates the gender difference rates of concussion in similar sports [69]. Women’s soccer has a higher rate of concussive injury than men’s both for overall rates of injury as well as for severe injury (6 % in women’s vs. 3.9 % in men’s) [76, 77]. In lacrosse women again lead men in rate of concussive injury overall (9.8 % of all injuries vs. 8.6 % injuries) [78, 79]. Most often lacrosse injuries are due to a stick to the head or contact with another player. Concussive injuries appear to have increased since 1995, mostly in men’s lacrosse [79]. This increase is speculated to be due to changes in helmet design that while increasing mobility and decreasing helmet weight may have decreased dissipation of impact forces to the head [79]. Risk for concussion was not as high in women’s field hockey as other sports but continued to be higher during games, with concussions representing 5.4 % of serious game injuries [80]. Concussion rates increased among many of these sports across the study period, but this was generally thought to be due to increased awareness and monitoring, rather than increases in actual injury.

Women’s sports, such as gymnastics and cheerleading, are often overlooked as activities that may predispose the athlete to an injury. Rates of injury are relatively low in collegiate gymnastics (0.40 per 1,000 athlete exposures during competition; 0.14 per 1,000 athlete exposures during practice), with most of the injuries secondary to handstands or related moves [81]. For overall rates of injury in gymnastics, concussion represents only 1.7 % of injuries [82]. Concussion injury rates in cheerleading, as surveyed in high school, collegiate, and all star squads, were relatively similar to other women’s sports, with concussion representing 4 % of injuries experienced in cheerleading. Injury was most often incurred during partner stunts, pyramids, or tumbling [83]. As cheerleading continues to include more gymnastics and partner stunts, and as participation rates increase, injury rates may continue to trend upward as they did in the most recent study of the sport.

In professional sports, data related to injury rates are not as widely available. The professional sports organizations that have published reports on the incidence of brain injury are the National Football League (NFL), the National Hockey League (NHL), and the Federation Internationale de Football Association (FIFA). The NFL has published a series of articles examining concussion-related data and programs. The rate of concussive injuries during games was estimated as 0.41 per NFL game [84]. The cause of most concussions involved impact from another player’s helmet (67.7 %), followed by impact with other body regions of another player (20.9 %) and contact with the ground (11.4 %). The primary symptoms noted after injury were headache (55 %), dizziness (41.8 %), and blurred vision (16.3 %); LOC was noted in only a small number of cases (9.3 %). Players who were most likely to be involved in a concussive event were quarterbacks, wide receivers, tight ends, and defensive secondary players. Repeated concussive injury was noted in 160 players during the study period for this series of reports, with 51 players experiencing three or more concussions during the study [85]. Of players that experienced concussion, almost half returned to play during the same game (49.5 %) [86]. Only 8.1 % of injuries required more than 7 days to return to play [87].

Data from the National Hockey League reflect an incidence rate of 1.8 concussions per 1,000 player hours [88, 89]. Rates of injury declined over the seven season study period, likely due to increased awareness and education, but it is notable that the time lost due to concussion increased over the study period with a median time loss of 6 days per concussion [88]. This likely reflects a stricter adherence to return-to-play protocols with greater attention to adequate rest to prevent further injury.

In professional soccer, FIFA’s retrospective analysis of players who suffered head and neck injuries during the course of play documented that 11 % of the 163 injuries identified were concussions [90]. The most common causes of injury were aerial challenges and use of the upper extremity, rather than heading which caused only one injury during the study period. Though incidence appears to be rising in professional sports, authors continue to note that this is likely not due to an increased injury rate but rather to an increased awareness to the issue of concussion and a need to document recovery prior to return to play.

With over 1.6 million individuals deployed to a combat environment since 2001, there is a significant portion of the population that is placed at high risk for incurring a TBI [91]. Prevalence rates of TBI in Service Members are estimated to be between 10 and 20 % of those who are currently serving in the military [92–94]. Surveillance from the Defense and Veterans Brain Injury Center (DVBIC) reflects 220,430 traumatic brain injuries coded in the military medical record from September of 2001 to the second quarter of 2011 [95]. Though larger numbers have been reported in the literature and in the media, these may be overestimates of the true incidence and prevalence of injury as they reflect screening data for TBI and likely include a number of false positives [96].

Screening data are usually obtained from the Post-Deployment Health Assessment/Post-Deployment Health Re-Assessment (PDHA/PDHRA) from the DoD or the Veteran’s Health Administration’s (VHA) TBI Screening Questionnaire [97]. These measures are used to determine if the Service Member or veteran was involved in events that placed them at risk for TBI and if they continue to have symptoms at the time of screening; follow-up evaluations with a provider are used to determine presence of TBI and etiology of current symptoms. As the military continues to develop their care model in theater, there are now mandatory evaluations in place for those who are felt to be at risk for TBI [98], with prescribed algorithms for follow-up care. Data are forthcoming from this effort and have begun to inform military medical leadership regarding the etiology of injuries suffered in theater, time needed for recovery, and casualty rates. Screening data from the PDHA/PDHRA have not been published to date. However, multiple survey efforts, primarily of Army personnel, find an estimated prevalence rate for mTBI of 10–20 % of Service Members surveyed [92, 99, 100]. There is some question as to whether the finding of continued symptoms associated with an injury event with either loss of, or alteration of, consciousness truly reflects mTBI and not another associated disorder (e.g., PTSD, pain-related disorder, or depression) [92].

Though combat-related or weapon-related TBI is seen as a signature injury in the cohort of Service Members who have served in Iraq and Afghanistan, TBI is actually a significant cause of hospitalization for Service Members prior to the current conflicts and remains a significant cause of hospitalization in the non-deployed population with the rate exceeding that of combat-related TBI (74.6 vs. 50.3 per 100,000 service members) [101].

VHA has screened for TBI in approximately 518,775 veterans of the current conflicts from April of 2007 to March of 2011 who have presented to VA medical facilities [102]. Of that number, 97,000 individuals have screened positive and were referred to secondary level evaluation. Of those, who screened positive, 72,623 individuals were referred for a secondary evaluation during which their symptoms were examined in more detail and full clinical evaluation was performed. Following that secondary evaluation, 40,154, or 7 % of the total of those screened, were found to have a symptom presentation and history consistent with mTBI.

The majority of TBIs diagnosed in the military and in VHA are consistent with mTBI (76 %), with the primary etiology being blast-related. A blast TBI results from the Service Member being proximal to an explosive, such as an improvised explosive device (IED), rocket propelled grenade, land mine, or other artillery or bombs [103]. There are different levels of blast-related injury defined in the literature: (1) primary blast is a result of the rapid overpressurization and underpressurization of surrounding air as a result of the shock wave, (2) secondary injury results from blast-related fragments or shrapnel, (3) tertiary injury incurred either from falling debris or the Service Member being propelled into an object or their vehicle being propelled by the explosive, (4) quarternary injury from the associated physical processes that result from detonation such as heat injury or toxic detonation products, and (5) quinary injury, resulting from environmental hazards that may remain after the bomb detonates [103–106]. Following blast-related TBI, the other major causes of combat-related TBI are consistent with the major causes of TBI in the civilian population with motor vehicle accidents or land transport accidents, falls, and sports and recreational injuries rounding out the major causes of TBI within the military population. In those with severe and penetrating TBI, the four most common etiologies are blast, motor vehicle accident, falls, and gunshots to the head or neck [107].

Investigation of TBI in theater-based military treatment facilities (MTFs) is beginning to emerge in the literature [108]. Review of records from OIF by the Naval Health Research Center for the period of March through September 2003 noted ICD-9 codes consistent with TBI-related diagnoses in 115 personnel. Most of the injuries were due to combat activities (71 %) with a smaller proportion related to non-battle injuries (16 %). Seven percent of the injuries were secondary to vehicle accidents. Thirteen percent of TBI patients were killed in action or died of their wounds. Concussion was the most common injury code, especially among the non-battle injuries (94 %). Skull fractures and other head wounds were prominently noted in those wounded in action or killed in action (26–33 %). The majority of injuries were caused by IED (52 %); in those who died, gunshots and mortar rounds made up a larger proportion of this group (40 %). The leading causes of non-combat injuries were blunt trauma and motor vehicle accidents. Most often those who were wounded in action had a higher percentage of other bodily injury with face (50 %) and extremity injuries (31 %) representing the majority of other areas of injury. Two thirds of those in the study were wearing protective equipment, generally a helmet and body armor, most of those injured reported a mean of 2.5 types of protective gear worn at the time of injury. Return to duty rates were relatively high in the population, with 46 % of those wounded in action returning to duty and 67 % of those with non-battle injuries returning to duty. Of those with a mTBI who were discharged from service, 29 % of the discharges were disability-related (not specific necessarily to TBI). Of those with moderate to severe injury, 100 % of discharges from service were disability-related.

In a 10-year study of TBI hospitalizations in the Continental United States (CONUS) or European MTF’s conducted with records from 1997 to 2006, 110,392 Service Members had at least one medical encounter for TBI and there were 15,372 hospitalizations for TBI, with falls and land transport accidents representing the primary etiology for injury. Hospitalization rates have increased over the course of the conflict, vary by Service branch and phase of the conflict, and reflect a higher rate of weapons-related injuries. The Service Member hospitalized with TBI is generally a younger man, who is at the rank of junior enlisted or non-commissioned officer (E1–E5), and tends to serve in the Army or Marines. In examining the early stages of the conflict, Heltemes and colleagues [109] determined an incident inpatient hospitalization rate for TBI of 10.4 Service Members per 10,000 troop strength (1,213 personnel in total) in either Landstuhl (German-based medical center) or in CONUS Regional Medical Centers. This study found that of the sample, only 3 % died of their injuries during hospitalization. The majority of the diagnoses were intracranial injury without skull fracture (59.7 %), with 39.3 % suffering a fracture of the skull. These data likely represent an underestimate of incident TBI hospitalizations as they did not account for in-theater deaths or hospitalization.

More recently, a study of all TBI hospitalizations in the US Army for the period of September 2001 to September of 2007 documented that 46 % of the hospitalizations were for severe TBI, 54 % for moderate, and less than 1 % were for mild [110]. Though 65 % of the severe injuries were related to explosions, almost half of the injuries were related to non-combat causes. Overall about 0.14 % of service members in OEF and 0.31 % of those serving in OIF had TBI-related hospitalizations [110]. In a separate study of the Army hospitalization rates, Ivins and others [101] found a 105 % increase in TBI hospitalizations in the Army from 2000 to 2006, with a 60-fold increase in those injuries attributed to weapons. Of the 2,959 cases that presented to an Army medical treatment facility, the majority of cases was mild in severity and was associated with extracranial injuries. Finally, studies that have assessed for TBI in those who were hospitalized for other conditions that warranted inpatient treatment noted about 20–30 % have TBI in addition to their other injuries [91, 111].