Trends in concussion on high school sports: A prospective 11-year study
Lincoln AE, Caswell SV, Almquist JL, Dunn RE, Norris JB, and Hinton RY. Am J Sports Med. 2011 May;39(5):958-63.
It is important to understand injury incidence by sport because it provides information about participation risk as well as factors they may influence injury risk. Historically, the highest rates of sport concussions have been reported in contact sports such as football, soccer, and ice hockey. In sports with both genders (e.g., soccer), females tend to have similar or higher concussion injury rates compared to males. In the current study, the authors prospectively reported concussion injury in athletes from 25 public high schools from 1997 to 2008. Certified athletic trainers were data collectors that used the Standardized Assessment of Concussion (SAC) and ImPACT to determine concussion occurrence during games and practices.  Exposure (game or practice) and injury data were reported by sport (12) over an 11-year period. The authors reported a total injury rate of 0.24 concussions per 1000 exposures with a 4.2 fold increase over the 11-year period (0.12 in 1997 to 0.49 in 2008). Football accounted for over half the concussions and highest injury rate (0.60 concussions per 1000 exposures), followed by women’s soccer (0.35 concussions per 1000 exposures). When examining sports with males and females, girls had higher concussion rates in soccer, basketball, and softball/baseball.
I thought this was a very good study for two reasons. First, personnel trained in injury identification (certified athletic trainers) collected data in a standardized manner using a concussion definition. Athletic trainers know concussion pathomechanics well and interact with the athletes daily, increasing the likelihood of identifying changes in athlete behavior due to injury. Second, concussion data were presented as injury rates (injury occurrence per number of opportunities or exposures). This is more meaningful than presenting only injury occurrence data. The injury rate data suggest that on a high school football team with 50 players with 5 events per week for 16 weeks, an athletic trainer should expect approximately 2 to 3 concussions. 
Two interesting study findings were that concussion injury rate increased during the course of the study and female high school athletes tended to have higher concussion injury rates compared to male counterparts. The increase in injury rates may represent a true increase in the rate of concussions or the enhanced ability of athletic trainers to identify concussions secondary to the improved dissemination of guidance on concussion detection and management as well as the use of sideline tests (e.g., SAC). Athletic trainers involved with the study may have also become more sensitive in detection methods. For example, if the athletic trainer saw a potential concussive event, then they may have questioned the athlete versus waiting for the athlete to initiate the conversation (which is appropriate a clinical action). 
This study will continue to fuel the debate regarding gender differences in concussion risk. Mechanically, female athletes may have less ability to stabilize and protect the brain from injury due to less head mass and neck muscle strength versus their male counterparts. Based on Sir Isaac Newton’s 2nd law, Force = Mass x Acceleration, the lower the mass (and strength) the greater the head acceleration and injury risk upon head impact force. Regardless of sex, the study results indicate the need for awareness of the clinician during all sporting events as concussions can occur in any sport.  
Written by: Ryan Tierney
Reviewed by: Jeffrey Driban