Traumatic Brain Injury Demographics, Philip Schatz

Epidemiology, incidence, cause, and trends in head trauma have been widely studied. Annegers, Grabow, Kurland & Laws (1980) documented trends in head injury in Olmstead County, Minnesota between 1935 and 1974. Jagger, Levine, Jane & Rimel (1984) studied the characteristics of occurrence of head trauma in a predominantly rural section of north central Virginia. Kraus, Black, Hessol, Ley, Rokaw, Sullivan, Bowers, Knowlton & Marshall (1984) identified incidence rates among the residents of San Diego, California during 1981. Gordon, Mann & Willer (1993) reported characteristic data collected from a TBI database (Dahmer, et. al., 1993) collected from five individual hospitals in New York, Richmond, Detroit, Houston, and San Jose. Summaries of epidemiology, occurrence, and outcome studies have been performed (Sorenson & Kraus, 1991; Kraus, 1993), citing several other epidemiological and characteristic studies, and can be used for defining baseline characteristics of a TBI population.

The incidence of TBI ranges from 132 to 367 per 100,000 people, with an average annual incidence rate of 200 brain injuries per 100,000 persons (Sorenson & Kraus, 1991; Kraus, 1993). 300,000 mild TBI hospitalizations per year are documented, with many more mild injuries occurring that do not require medical observation and/or intervention (Kraus et al, 1984). Kay (1992) estimates that 1.3 million mild TBIs occur each year in the United States. Age distribution of head injury is highest in young adults, ages 15 to 25 (Whyte & Rosenthal, 1988). This pattern is documented in all incidence studies reviewed by Sorenson & Kraus, (1991) and Kraus (1993). Significant effects of gender on head injury incidence have been consistently noted, with males outnumbering females by at least 2:1 (Whyte & Rosenthal, 1988). Comparing demographic and social characteristics of their TBI model system to other studies, Gordon, et. al. (1993) found their brain injured subjects were 77% male, comparable to other studies (70%, 78%, and 82%). Kraus (1993) summarized nine studies of incidence of head injury in the United States, with a mean percentage of males being approximately 70%.

Cause of brain injury is difficult to compare across epidemiological studies due to different classification schemes. In general, 50 to 60% of all brain injuries result from motor vehicle-related incidents (Sorenson & Kraus, 1991). One summary of incidence reports sub-divided motor vehicle-related brain injuries into specific subcategories (Kraus, 1993); approximate means of data provided describe percentages for motor vehicle occupants (73%), motorcyclists (12%), pedestrians (10%), and bicyclists (5%). Second to motor vehicle-related brain injuries are falls, with reported averages ranging from approximately 20% (Jagger, et. al., 1984) to 29% (Annegers, et. al., 1980). Approximate average of falls from nine incidence studies (Kraus, 1993) is about 25% of all brain injuries. Percentage of interpersonal assaults range from 4% (Annegers, et. al., 1980) to 12% (Kraus, et. al., 1984). Other causes of head injury, such as sports-related activities, recreational activities, and suicide attempts are, at times, collapsed into an "other" cause category, making it difficult to determine exactly what percentage is attributed to each specific cause. Kraus, et. al. (1984) placed head injuries caused by organized sporting events, use of pedal cycles not in traffic, and pedestrian conveyances such as roller skates and skateboards into the "sports and recreational activities" group, while placing riders of animals in the "transportation-related" group. Annegers, et. al. (1980) created separate groups of head injury causes, such as automobile, falls, recreational, bicycle, occupational, assault, motorcycle, gunshot, snowmobile, and other; they placed riders of animals in the "recreational" group. (due to limited research, it is unclear exactly how many TBI's are the direct cause of falling livestock....).

Seatbelt use was investigated by Jagger, et. al. (1984), with only 4% of the 10-39 age group reporting seatbelt use. Gordon, et. al. (1993), reported only 24% of subjects involved in motor vehicle accidents were wearing seatbelts, with no significant effect of demographic factors on seatbelt use. Similarly, helmet use (for bicycle and motorcycle accidents) was studied by Gordon, et. al. (1993), with only 16% of subjects involved in bicycle or motorcycle accidents wearing helmets. Unfortunately, there was no report of effect of seatbelt or helmet use on outcome.

Alcohol use at the time of injury was investigated in several epidemiology studies reviewed by Kraus (1993). More specifically, alcohol use was documented as 9% through 79% in multiple studies of brain injured subjects. Gordon, et. al. (1993) reported 51% of the subjects included in their database were intoxicated at the time of their brain injury, with individuals in the age ranges of 26-35 and 56-65 most likely to be intoxicated at the time of their injury.

Gordon, et. al. (1993) compared the demographic and social characteristics of their study with two other studies, reporting from 44 to 55% of subjects had never been married at the time of their head injury. This, of course, is directly related to the young age of the head-injured population. In their study of 325 brain injured subjects, they found 55% had never been married, 26% were married, 12% were divorced, 4% were separated, and 4% were widowed (Gordon, et. al., 1993). With respect to education, Gordon, et. al. (1993) identified a range of 38 to 49% of subjects who had not completed high school at the time of their head injury. In their study, 40% of the subjects obtained a pre-high school diploma (i.e., completed grade school or middle school), 27% a high school diploma, 21% an associate degree or attended some college, 7% a bachelor's degree, 3% a trade school, and 2% an advanced degree.

In summary:

  • 50-80% of all TBI's are mild
  • Many mild TBI's go unreported
  • 1.3 million mild TBI's occur each year in the US (Kay, et. al, 1992)
  • Incidence of mild TBI is highest in Males ages 15-35
  • Much is still unknown...

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