A concussion is an injury to the brain that results from direct trauma to the head or indirect trauma to the body transmitted to the head.1 One of the most common causes of concussion in young people is participation in sports.2 Sports-related concussion (SRC) seldom involves loss of consciousness, which may mean it is under-recognized, as initial clinical presentation can be subtle. Some sources estimate 300,000 SRCs occur annually in the United States,2 making this a very significant healthcare problem. This review will focus on the primary and secondary prevention of SRC and risk factor modification to achieve that goal.
How to best prevent concussion has been debated for many years, but many commonly suggested interventions may not lower the incidence or severity of this injury. Equipment choices such as helmets worn on the head have historically been thought to help protect the brain; however, current opinions hold that although helmets may prevent skull fracture, they may not limit the acceleration of the brain enough to prevent concussion.3,4
Some authors believe that susceptibility to concussive brain injury is such that it is inevitable in certain sports.5 Hollis et al.5 showed that 7% of a 3,207 male community of rugby players (aged 15–48 years) sustained a concussion within 10 hours of time playing the game, increasing two-fold to 14% within 20 hours of game time. Players reporting a recent history of concussion were 20% more likely to sustain a concussion after 20 hours of game time compared with those with no recent history of concussion. This highlights a common thread across all sports, in that a previous concussion is the greatest risk factor for sustaining another one. Therefore, primary prevention of the first concussion is paramount.
Intrinsic Risk Factors
There may be a percentage of the general population that is genetically predisposed to sustaining a concussive injury to the brain from the same magnitude of acceleration (or force) that other people can tolerate without injury. This may be a susceptibility at a cellular level related to neurotransmitter excitation and is postulated to be related to the gene APOE4, although this remains unsubstantiated.6,7 Biomechanical properties of an athlete’s head, such as the greater thickness of the skull (Figure 1), more cerebrospinal fluid, presence of Arnold-Chiari malformation, and properties of the cervical spine such as limited strength, range of motion, and flexibility may influence susceptibility to injury. It is possible that there is natural selection of children who migrate toward sports involving contact and collision, and that children who may have suffered concussions from contact during playground and other unstructured activities (whether or not diagnosed by a physician) ultimately opt out of contact sports due to the perception that this is something they could not do without getting hurt.
Increased skull thickness is sometimes cited as a risk factor for concussion.
Age and Gender
Younger age has been established as both a factor for greater risk of sustaining a concussion and of sustaining a more severe concussive injury that takes longer to resolve.8 Data also show that concussion rates are higher for females compared with males in similar sports.8 However, there is limited published research defining or quantifying what this difference may be between males and females. Proposed theories for this gender difference include females’ weaker neck muscles and greater likelihood to report symptoms.
Neck Muscle Strength
Although many intrinsic risk factors are not modifiable (eg, age, gender), others may be influenced. Neck strengthening has been suggested to be beneficial, although it is unclear whether activation of musculature can occur within a rapid enough interval to have any bearing on how much the brain is accelerated from trauma. Anticipation of impact is probably crucial,9,10 and it may be a balance between the cervical flexor and extensor muscles that stabilizes the head rather than absolute strength.11 Younger athletes’ relatively large head in comparison to their body and relatively weaker necks have been suggested as major risk factors for concussion in younger, elementary-age children.
There does appear to be a discrepancy in neck strength between adults and children playing sports such as rugby that require head, neck, and upper torso stability.12 It is possible to strengthen the neck with a 4- to 6-week program to prepare athletes for participation.13
Preexisting Neurologic and Psychological Conditions
The presence of comorbidities such as preexisting attention-deficit/hyperactivity disorder (ADHD), migraine headaches, or mood disorder seems to predispose child athletes to sustaining a longer duration of symptoms after a concussive injury.14 Although it is not always possible to determine why this may be the case, it is likely that for patients with these disorders, a concussion exacerbates their preexisting symptoms and makes them more difficult to control. Additionally, psychoactive drugs may alter behavior and/or reaction time, which may increase the risk of sustaining a brain injury and inhibit the brain’s recovery. Patients with ADHD also have impulsive behavior that may place them at increased risk for concussive injury.
Extrinsic Risk Factors
Previous Concussive Injury
A previously sustained concussion remains the factor most predictive of a subsequent injury. The 4th International Conference on Concussion in Sport was held in Zurich in 2012. The resulting consensus statement, commonly referred to as the Zurich guidelines, described “concussion modifiers” or risk factors that may predict a longer recovery (Table 1).8 Additionally, the presence of such factors may signify increased risk for subsequent concussions with more prolonged recovery and, therefore, would influence overall risk stratification of an athlete wishing to return to a sport that has a relatively high concussion injury rate. Once such risk stratification indicates that the risk exceeds the benefits of participation, a physician may recommend that the child no longer participate in that sport or others with a similar risk.
Concussion Modifiers: Risk Factors that May Predict Prolonged Recovery
After someone has had three concussions, some authors have suggested there may be permanent neuropsychological deficits.15–17 With increased awareness of SRCs, it is important that physicians explore the details of each concussion, both to identify possible modifiers and to determine that each concussion was a unique event and not two traumatic events in the same period that may represent incomplete recovery between them. It is this author’s opinion that there is no magic number of concussions that should mean an athlete is disqualified from participation in sport. However, it is reasonable to consider a prolonged period of time away from contact sports for athletes who have accumulated three or more concussions in a single season or before age 18 years. Such an athlete may be in a better position to assess the risks and benefits of contact sports once their brain is fully developed as an adult. Any athlete who has had a prolonged recovery (longer than 3 months) that has influenced his or her school performance should also strongly consider a prolonged break from contact sports given the elevated risk of concussion recurrence. Any such decisions should be made on a case-by-case basis and include a conference among the athlete, the parents, and the physician. Referral to a specialist with expertise in SRC is recommended if a physician is not comfortable making a determination regarding return to sports.
Helmets and Other Protective Equipment
Given that rugby is a collision sport involving players tackling one another with minimal protective equipment, one hypothesis frequently discussed is that sports with helmets must be safer. Head injuries were recorded at an incidence of 4.5–8.1 per 1,000 hours of youth rugby exposure.3,18 In comparison, football, has a reported rate of 6.6 per 1,000 hours of exposure. Some authors have noted increased concussion rates within the same sport when players adopt headgear,19 perhaps due to an increase in perceived safety and greater risk-taking behavior. Although helmets are mandatory in sports such as football, ice hockey, and men’s lacrosse (Figure 2), current consensus has been that headgear should not be used in other sports such as soccer and women’s lacrosse.3 Soccer headgear has not been shown to be effective in reducing risk of concussion, although it may protect soft tissue structures around the head.20 The regulations for women’s lacrosse mandate a “halo” of protected space around the head of player, a method thought to be a superior to using a helmets (as in men’s lacrosse) for limiting head trauma.
Helmets are mandatory in men’s lacrosse.
A study of the comparison between helmet age or brands in high school football in Wisconsin has also failed to show any difference in concussion incidence.21 A helmet that is in good condition and fits the athlete well is really the only important consideration at present. Winter sport helmet use has led to decreased severity of head injury in skiing and snowboarding,22 but again does not necessarily prevent concussion. Mouth guards have been promoted as potentially beneficial in preventing concussion, but this hypothesis remains unproven.23–26
Choice of Sport Participation and Style of Play
Children may sustain concussive injury in many activities, such as riding a bicycle, being involved in an altercation, being a passenger in a motor vehicle accident, or falling down stairs. It is difficult to quantify concussion risk for such activities. Koh et al.27 attempted to estimate differences in concussion incidence between various contact sports including football, soccer, ice hockey, rugby, boxing, karate, and tae kwon do. It is often very difficult to directly compare injury incidence between sports because there can be a large variation in how an injury is defined, how a concussion is diagnosed, and how it is reported. High school football has been estimated to result in 5%–15% of its participants sustaining a concussion each season.28,29 Given that the actual playing time in football is so sporadic and limited, this likely represents a high likelihood of concussion per minute of actual exposure time. In sports that athletes participate in continuously, such as soccer, lacrosse, and rugby, the much higher activity participation volume may result in a commensurate concussive injury rate, but the actual risk of being injured while participating at any given time is perhaps less. There will also be differences between playing positions both in terms of playing time and activities expected in a specific position. In football, a wide receiver who plays the entire game and is frequently thrown the ball, particularly over the middle of the field where there are more defensive opponents, will be at greater risk than a lineman who is brought in for limited plays.
Reckless behavior will always place an athlete at greater risk for injury. Aggression is a term often used to describe assertive play in sport and should not be confused with its definition outside the playing field, which confers intent to harm. The Zurich guidelines8 do not recommend discouraging competitiveness/aggression in sport, but instead encourage sporting organizations to appropriately address reckless and violent behavior and to actively promote fair play and respect.
Youth coaches have a very important role in helping athletes develop skills in their sport such that they can perform activities with a minimal risk of injury. This becomes particularly critical in contact and collision sports where athletes must learn how to tackle one another and withstand contact without personally sustaining injury or causing injury to an opponent. Given that motor development peaks between age 8 and 10 years, this is likely a key period for young athletes to learn how to play their sport safely. Limiting contact in some sports until children are older may have deleterious effects if they are then less skilled but bigger and stronger when they learn to tackle.30,31 This may not be the case in all sports, as limiting body checking in hockey until players are age 13 years has not been shown to lead to higher injury rates later when compared with players who were allowed to start checking at age 11 years.32 It may be important to differentiate between skills fundamental to the game being played and those skills that can be introduced later without a deleterious effect. If proper technique is being taught, whether it be playing “heads up” football when tackling an opponent or heading a soccer ball purposefully with the forehead, the skill can be performed safely if appropriately supervised and coached. There may be a baseline skeletal maturity, muscle strength, and coordination necessary and the age at which these developmental milestones are achieved varies among individuals. Some organizations choose to provide arbitrary age guidelines for the introduction of contact, but there are no data to support this strategy.20
Rules and Refereeing
Playing a chosen sport within the rules of the game is a very important component of primary prevention of concussive injury. Rule changes appear to have a much more profound preventive effect than changes in coaching, equipment, or education. The National Football League has made changes in rules such as shortening the kickoff return distance by 15 yards, which has lowered the incidence of concussions and other injuries. There has been investigation showing decreased incidence of injury in youth ice hockey when the rules are enforced more stringently.33 Similarly, limiting contact in youth football practice decreases head impact exposure.34 Some argue that this will not likely reduce incidence of injury because concussion rates are much lower in practices than in games.
Some sports governing bodies have introduced stiffer penalties to try and diminish head injuries. In soccer, the deliberate use of the elbow to strike an opponent (Figure 3) is considered an act of violence and warrants a “red card” (immediate and permanent ejection from the game) according to Federation Internationale de Football Association (FIFA) rules.35 This type of event was noted to be responsible for approximately 50% of concussions in soccer, and is much more dangerous than the often-cited concern about the act of heading the ball.35 It is important that changes in rule enforcement continue to be audited for both the desirable changes in behavior that are expected and the subsequent injury rate. There will continue to be some identifiable risk of participation in sport, and many governing bodies seek to minimize this risk while maintaining the fabric of their sport.
An example of the illegal use of the elbow in soccer.
Knowledge Gaps among Athletes, Parents, Coaches, and Health Care Providers
Although a concussion must be preceded by a traumatic event that may not be avoided by awareness of what a concussion is, there is a huge potential to prevent cumulative injury if symptoms of a concussion are recognized by a coach/parent or athlete and appropriate treatment is implemented. Clinical presentations of concussion often present with a history of two or three traumatic events over the course of a game or tournament. If the initial traumatic event resulting in symptoms were appreciated and the athlete removed from play, then there is a much lower likelihood of prolonged recovery. Recognition that most concussions do not result in loss of consciousness has perhaps led to much improved awareness of more subtle presentations. However, there is much work that remains to be done with respect to education, as athletes continue to underreport symptoms of concussion. In one study, only 47% of football players documented to have had a concussion actually reported their symptoms.2,36
Education of health care providers is equally important, as returning a symptomatic athlete to play by a well-meaning pediatrician may contribute to worse outcomes, including death from second-impact syndrome or permanent disability. Pediatricians can find up-to-date information about concussion evaluation and management, including return to play and return to classroom guidelines, in two recent clinical reports from the American Academy Pediatrics.37,38
The “Lystedt Law” in Washington State has pioneered legislative efforts to make sure concussions are managed correctly once identified.39 This law requires (1) schools to provide concussion educational materials and guidelines for athletes, coaches, and parents; (2) parents and athletes to sign informed-consent forms acknowledging the dangers of concussions before participation in sports; and (3) that any student showing signs of a concussion must be evaluated and cleared by a licensed health care professional before being allowed to return to practice or competition.39,40
As of November 2013, all 50 states have followed suit and have concussion legislation in place. Although this is a step in the right direction, whether the health care professional provides appropriate clearance is dependent on his or her knowledge and experience with concussion. Unfortunately, experience alone does not guarantee that a physician has been made aware of the change in climate regarding concussion in sport,1,7,8,41,42 and continuing medical education efforts should be geared toward universal understanding of this difficult topic. The era of players being allowed to resume participation on the same day of injury if their symptoms resolve on the sideline has well and truly passed. Likewise, the use of grading scales to attempt to quantify the severity of a concussive injury in order to predict timeframe for return to play has also been consigned to history. Unfortunately, such events and processes continue to be propagated, mostly due to lack of awareness. A compulsory annual education module (Rugby Smart) in New Zealand did result in a lower incidence of concussive injury in rugby,43 an idea that might well be replicated in other sports.
Concussion often occurs during participation in sports. Children and parents can choose a sport that they enjoy and benefit from while understanding the risks that participation entails. Contact and collision sports are not suitable for everyone; however, there is currently no good way to determine this suitability. Children with medical problems such as migraine headache, ADHD, or mood disorder may be at greater risk of severity from a concussive injury. There is no equipment that provides protection from a concussive injury, although other injuries may be prevented with use of helmets and mouth guards. A contact sport should be adequately coached and officiated, and opponents should be respected and the rules of participation honored. Parents, coaches, and athletes should be made aware of the signs and symptoms of concussion so they know when to discontinue participation and potentially avoid a cumulative injury. Pediatricians and physicians caring for child athletes should remain up-to-date on concussion recognition and management to aide their decision-making in determining return to play.