The most obvious difference between combat-related concussion and sports-related concussion is the mechanism of injury. Blasts from various forms of explosive devices are a common cause of combat-related injury in the military and are the most common cause of combat-related concussions in the current conflict in Afghanistan. There are four different mechanisms through which a blast can cause injury:
Primary Blast: Atmospheric over-pressure followed by under-pressure or vacuum.
Secondary Blast: Objects placed in motion (shrapnel) by the blast hitting the service member.
Tertiary Blast: Service member being thrown by the blast.
Quaternary Blast: Other injuries from the blast such as burns and crush injuries.
As a result, virtually all service members who sustain a concussion following a blast are thought to have injury not only from the blast, but also from blunt trauma. For example, this can happen when service members are travelling in a vehicle that is blown up by an improvised explosive device. In addition to the blast wave, they are likely to hit their head against the interior of the vehicle.
In sports the most common cause of concussion comes from head-to-head impacts in helmeted athletes. In the United States there are an estimated 300,000 sports-related concussions each year.1 Sports are second only to motor vehicle crashes as the leading cause of civilian concussions in those aged 15-24.
Concussions are far more likely in football (47.1 percent of the 1,936 concussions that occurred in high school athletes during the 2008-2010 school years) than any other sport. The next riskiest sports are boys ice hockey and boys lacrosse.2 The injury rate is six times higher for competition than practice.
Types of Injuries
Most experts consider concussion to be a disruption of brain function that is not associated with significant structural brain injury. Imaging studies are not usually done for concussions because symptoms usually resolve quickly. More sophisticated imaging studies have been developed that can show damage to the brain’s pathways. Recently very high-definition MRI techniques have been developed, such as Diffusion Tensor Imaging and Susceptibility Weighted Imaging, which do show evidence of nerve damage in 30-40 percent of service members who are symptomatic from a concussion.3
There is no clear evidence that the types of combat-related concussion are significantly different for blast or blunt trauma from sports. Moreover, recent neuropsychological studies have found no measurable differences in cognitive performance between blast and blunt injuries.4
Individuals who sustain a concussion often do not seek out medical attention. The reasons for this are that the symptoms of concussion quickly subside in most subjects within seconds or minutes after the injury. Also it is the culture among service members and athletes to ignore signs and symptoms of concussion and return to the fight or play as quickly as possible. Thus, caregivers and coaches must be vigilant for the signs and symptoms of TBI in any service member or athlete who may have sustained a blow to the head.
In 2011 the DoD instituted a requirement that all service members exposed to a blast event (within 50 meters), or who were inside a vehicle or building exposed to a blast, must be removed from combat for at least 24 hours and be medically evaluated prior to return to duty. Likewise, the National Football League instituted rigid new requirements that state, in part: "Once removed for the duration of a practice or game, the player should not be considered for return-to-football activities until he is fully asymptomatic, both at rest and after exertion, has a normal neurological examination, normal neuropsychological testing, and has been cleared to return by both his team physician(s) and the independent neurological consultant." These new policies were instituted in direct response to the culture of the service members and players wanting to return to combat/play too soon and not being forthcoming about their symptoms.
In both the military and sports, the initial focus during the acute evaluation following a concussive event is assessment of cognitive functioning and balance. The service member or athlete will typically be asked a series of orientation questions and will have simple tests of short term and delayed memory. They then will be asked to perform a balance test. In the military, these tests are codified as the Military Acute Concussion Evaluation (MACE) which consists of standardized testing of cognition, neurologic functions including balance, and a symptom screen. All corpsmen and medics are expected to use the MACE during evaluation of service members suspected of having a concussion. In high school, collegiate, or professional sports programs there is no universally accepted acute evaluation tool like the MACE, although the Sports Concussion Assessment Tool-2 (SCAT-2) is similar and is used by many sports programs.
Those individuals who remain symptomatic 24-48 hours after the injury are often referred for further testing. In-theater service members will often be referred to a concussion care center and will likely have more detailed cognitive testing with the Automated Neuropsychological Assessment Metric (ANAM). Post-injury test results can be compared with pre-deployment tests, and serial studies can be done to follow recovery from the cognitive deficits sustained from the concussion. Increasingly high school, collegiate and professional sports teams are obtaining pre-season neurocognitive baseline testing so that cognitive deficits can be detected more easily after a concussion.
The vast majority of those with blast and sports-related concussion have a complete recovery, usually within minutes or hours. Risk factors for prolonged symptoms include loss of consciousness associated with the impact, history of previous concussions, or a history of certain behavioral problems such as anxiety.
For the small proportion who remain symptomatic, the most common post-concussion symptoms are headaches, sleep disturbances and balance problems or dizziness. Approximately 50 percent of those with post-traumatic stress disorder have had a concussion, and approximately 50 percent of those with a concussion who remain symptomatic for weeks or months will develop post-traumatic stress disorder. There also is concern that multiple concussions may lead to prolonged or permanent cognitive and other neurologic problems. Please see Cumulative Concussions.
1 Gessel LM et al. Concussions among United States high school and collegiate athletes. J Athl Train. 2007; 42:495-503.
2 Marar M et al. Epidemiology of concussions among United States high school athletes in 20 sports. Am J Sports Med. 2012; 40:747-55. Epub 2012 Jan 27.
3 Mac Donald CL et al. Detection of blast-related traumatic brain injury in U.S. military personnel. N Engl J Med. 2011; 364:2091-100. Cubon VA et al. A diffusion tensor imaging study on the white matter skeleton in individuals with sports-related concussion. J Neurotrauma. 2011; 28:189-201.
4 Lange RT et al. Neuropsychological Outcome from Blast versus Non-blast: Mild Traumatic Brain Injury in U.S. Military Service Members. J Int Neuropsychol Soc. 2012; 30:1-11.