As participation in high school sports continues to increase, ATs will continue to be heavily relied upon to diagnose and treat concussions. Sport-related injury surveillance systems can provide the scientific data needed to calculate injury rates, monitor patterns of injury, and identify risk factors. For example, our data demonstrated differences in sport-related concussion among sports and between the sexes and levels of play (ie, high school versus collegiate). By identifying patterns that could predict concussions, we may be able to reduce concussion rates through targeted, evidence-based interventions.
In our study, concussions represented 8.9% of all high school sport-related injuries. This amount is higher than the 5.5% reported by authors12
of a study of high school athletes conducted a decade ago using similar definitions of injury and exposure and the 7.5% reported in authors of a more recent North Carolina study who included all concussions regardless of time loss.9
One potential explanation is that the prior research included sports not included in our study, such as girls' field hockey12
and track and field,9
which have relatively low concussion rates. However, the higher concussion rate reported here may reflect an increased awareness of, and subsequent diagnosis and treatment of, concussions.22
Educational campaigns, such as the distribution of the “Heads Up: Concussion in High School Sports” tool kit by the Centers for Disease Control and Prevention, National Center for Injury Prevention and Control,23
have increased awareness of concussion symptoms among coaches, athletes, and parents. In general, contact with another person appears to be the risk factor responsible for most of the concussions among high school athletes (). Full-contact sports (eg, football and wrestling) as well as partial-contact sports (eg, soccer and basketball) had the highest competition-related rates of concussion.
In sports both sexes played in, high school girls had higher rates of concussion than boys. This trend, which was also seen among college athletes (), has been noted previously.11,12
In our study, sex differences in risk factors for concussion were also noted. In soccer, contact with the ground or with the ball was a more frequent cause of concussion in girls than boys (). Comparing baseball and softball, boys were more likely than girls to sustain a concussion after being hit by a pitch, a finding possibly attributable to the different pitching styles and balls. In soccer, more boys suffered concussions goaltending, whereas more girls sustained concussions defending. In basketball, more boys sustained concussions while rebounding and chasing loose balls, whereas more girls sustained concussions defending and ball handling. Such differences may be attributable to differences in the style of play.
One possible explanation for the observed sex differences in concussion rates is biomechanical differences. Barnes et al24
suggested that differences in concussion symptoms between male and female soccer players may be due to smaller head to ball ratios or weaker necks. Queen et al25
demonstrated that in children, an increased head mass resulted in decreased linear acceleration of the head. In a study of collegiate soccer players,26
females had 26% less total mass in their head and neck than males. In another recent study,27
females demonstrated greater angular acceleration and displacement of the head and neck. This movement was despite the earlier activity of the sternocleidomastoid muscle in females, which should have acted to stabilize and decrease acceleration and movement of the head.27
Although this acceleration may not play as great a role in soccer players, who learn to resist such forces with the head in practice and competition,26
tests using accelerative forces large enough to observe sex differences in soccer players have not yet been performed.26
Nevertheless, head and neck acceleration differences between the sexes may play a role in other sports.
Cultural explanations may also play a role in the observed sex differences in concussion rates. Traditionally, US society has tended to be more protective of female athletes.28
This may lead coaches, ATs, and parents to treat head injuries in female athletes more seriously or to delay their return to play. Similar cultural tendencies may encourage male athletes to play despite injuries or to avoid reporting injuries, particularly in certain sports. Thus, some boys suffering from head injuries may not report their symptoms for fear of being removed from play.29
A reluctance to report injury was demonstrated in high school football players30
: only 47.3% of players claiming to have suffered a concussion reported their injury. Underestimating the seriousness of the injury, not wanting to be withdrawn from competition, and not being aware of having suffered a concussion have been cited as reasons for underreporting concussion injury.30
We found that although rates of concussion were higher among collegiate athletes, concussions represented a higher proportion of all injuries sustained by high school athletes. This finding is contrary to the work of several authors,16,17
who reported that rates of concussions were higher among high school athletes than collegiate athletes. The potential for more playing time, lower-quality protective equipment, and lower skill level were suggested as reasons why a higher rate of concussion might be expected among high school athletes.16
Conversely, collegiate athletes play at a faster, more competitive level and are bigger and stronger than high school athletes,11
which some argue may increase the former's risk of concussion. The truth likely lies somewhere in between, and it may be that a lower level of skill leads to a higher proportion of concussions compared with other injuries at the high school level. Furthermore, greater intensity of play at the collegiate level may predispose those athletes to a higher rate of concussion, as well as increase the rate of other injuries and lower the proportion of all injuries that are concussions. Recently, however, only small differences were noted between head impact in high school and collegiate football players.31
Thus, the higher rates of concussion at the collegiate level may stem from the intensity of play leading to a greater number of impacts rather than greater force of impact.
This study, like all studies, had limitations. Eligibility was limited to high schools with NATA-affiliated ATs. Thus, although schools were selected to be nationally representative with respect to geographic location and school size, our findings may not be generalizable to schools without an AT. However, the increased quality of data provided by these medically trained reporters justified this inclusion criterion. Another potential limitation was our definition of injury.
Only time-loss injuries that came to the attention of the school's AT were included in the study. In addition, low-grade concussions that were not accurately diagnosed and concussions that did not keep the athlete out of play for at least 1 day were not captured. Therefore, concussion rates among high school athletes are likely actually higher than those reported here. Another potential limitation was the definition of an A-E as 1 athlete's participation in a practice or competition, rather than the more precise approach based on the minutes an athlete was exposed.32
This definition was necessitated by our use of ATs as reporters because it was not possible for high school ATs to be simultaneously present at all athletic practices and competitions to collect such detailed exposure data. Additionally, our definitions of injury and A-E mirrored the definitions used in the NCAA ISS, which enabled us to directly compare concussion rates among high school and collegiate athletes. Finally, although we used a weighting factor to estimate national numbers of high school concussion injuries, we were unable to apply weighting factors to the standard error when calculating confidence intervals and P
values because the NCAA ISS values were not based on national averages.
The rates of concussion among high school and collegiate athletes shown in this study are higher than those previously reported.8,11,12
Competition-related concussion rates were highest among full-contact sports (football and wrestling) and partial-contact sports in which player-to-player contact often occurs (ie, soccer and basketball). We found the rates of concussions among high school athletes were lower than those among collegiate athletes, whereas concussions comprised a greater proportion of total injuries among high school athletes. Additionally, for sports both sexes played, the rate of concussion as well as the proportion of all injuries attributable to concussions was higher among females. With an estimated 135
901 concussions occurring nationally among high school athletes participating in these 9 sports during the 2005–2006 academic year, we must attempt to identify methods for preventing these serious sports injuries.
Although the risk of sport-related concussion does not outweigh the many benefits of sport participation, preventive interventions should be implemented to decrease concussion rates to the lowest possible levels. Development of effective sport-related concussion preventive measures depends upon increasing our knowledge of concussion rates, patterns, and risk factors. Future studies are needed to further investigate potential interventions such as educational programs,23
improved protective equipment, increased conditioning, enhanced enforcement of sporting rules, and policy changes33
that might prevent concussions at both the high school and collegiate levels. For example, while enhanced officiating and rule changes may reduce sex differences in concussion rates by addressing differences in style of play, improved protective gear may need to account for biomechanical differences. Additionally, improved concussion management driven by a better understanding of concussion symptoms and symptom resolution time may reduce the long-term sequelae of concussions. We support current guidelines regarding concussion diagnosis, treatment, and athletes' return to play, but additional research is necessary to determine the validity of self-reported symptoms29
and symptom resolution as viable determinants of return to play. Furthermore, because no consensus as to the effects of multiple concussions exists,3–5
we believe caution should be exercised when clearing athletes with multiple concussions to return to play. Such caution may be especially pertinent to high school athletes who suffered concussions and then continue to play in college.