concussion, often goes underreported since period of unconsciousness may be negligible and medical attention may not be sought. Therefore the actual annual incidence of TBI is thought to be higher than currently estimated.

TBI is a major public health concern for civilians as well as members of the military. Each year, an estimated 1.7 million individuals in the United States sustain a TBI (CDC 2010). Of those, approximately 52,000 individuals die each year from their injuries. According to the U.S. Centers for Disease Control and Prevention (CDC), each year an estimated 124,626 people with TBI experience long-term impairment or disability from their injury (CDC 2011a).

TBI Classification Schemes

Head injuries have historically been classified using various clinical indexes that include pathoanatomical features, severity of injury, or the physical mechanisms of the injury (i.e., causative forces). Different classification systems may be used for clinical research, clinical care and management, or prevention. The classification systems most relevant to rehabilitation deal with severity as it relates to pace of recovery or expected degree of impairment. These include the Glasgow Coma Scale (GCS), posttraumatic amnesia (PTA), and others. Chapter 2 includes descriptions of these scales. One classification system is severity of the injury. TBI severity is generally graded in degree, from mild to moderate or severe. Severity can be graded in multiple ways, and each measure has different predictive utility, including determining mortality, morbidity, or long-term or functional outcomes. Determining severity is often based on the acute effects of the injury such as the individual’s level of arousal or duration of amnesia; these are measured by GCS, duration of unconsciousness, and PTA. It is important to note that severity of injury does not always correspond with severity of one or more impairments.

The majority of TBIs are mild, consisting of a brief change in mental status or unconsciousness. Mild TBI is also referred to as a concussion. While most people fully recover from mild TBI, individuals may experience both short- and long-term effects. Moderate to severe TBIs are characterized by extended periods of unconsciousness or amnesia, among other effects. The distinction between moderate and severe injuries is not always clear; as such, individuals with moderate and severe injuries are often grouped for research purposes. Throughout the remainder of this report, the committee refers to more severe injuries as moderate-severe TBI. The more severe the injury, the more severe and persistent the cognitive deficits—though clinical measurements do not always concur. Severity measures graded during the acute phase sometimes reflect variance due to medications used during resuscitation, substance use, and communication



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