Comparison of Head Impact Exposure Between Concussed Football Athletes and Matched Controls: Evidence for a Possible Second Mechanism of Sport-Related Concussion.
Stemper BD, Shah A, Harezlak J, Rowson S, Mihalik JP, Duma SM, Riggen LD, Brooks A, Cameron KL, Campbell D, DiFiori JP, Giza CC, Guskiewicz KM, Jackson J, McGinty GT, Svoboda SJ, McAllister TW, Broglio SP, McCrea M; CARE Consortium Investigators.
Ann Biomed Eng. 2018. [Epub ahead of print]
Take Home Message: Athletes with a concussion had greater exposure to head impacts on either the day of injury or in the season leading up to the injury compared to peers matched on the same team and playing the same position.
Authors conducting biomechanical concussion research have suggested that repetitive head impact exposure (lifelong or recent) may increase a player’s risk for concussion due to a decrease in concussive tolerance. However, much of this prior research involved no control group, a small cohort of athletes with a concussion, or only one competitive season. Therefore, the authors collected head impact data from the 2015-2017 fall and spring seasons at 6 institutions (part of the NCAA CARE Consortium) to determine differences in repetitive head impact exposure between 50 college football athletes with a concussion compared to healthy peers (~4 per concussed). Each team’s medical staff diagnosed a concussion with a standardized concussion evaluation. The authors selected a control group by finding athletes without a concussion, who participated in 33% of the season, and who were exposed to the same practice and game conditions per team and position. Head impacts were measured using the HIT System, embedded in each athlete’s helmet. The authors calculated head impact exposure for each athlete using the number of recorded head impacts and cumulative injury risk (cumulative severity based on the linear and rotational acceleration data). During the 6 seasons a total of 424,059 head impacts were recorded. Interestingly, athletes without a concussion sustained 4,589 head impacts with greater acceleration (linear and rotational) than the average accelerations among athletes with a concussion (~71g’s), and 249,160 head impacts with acceleration greater than the lowest magnitude of a concussive impact. However, 72% of athletes with a concussion recorded greater exposure to head impacts on the injury date or the season leading up to that injury date when compared to their matched controls. The authors found that 43% of the athletes with a concussion had the most severe head impact on the day of injury compared to their matched peers. Additionally, 46% of athletes with a concussion had the most severe head impact exposure for the season leading to the date of injury compared to their matched peers.
This is one of the first studies to take a large cohort of athletes and compare athletes with a concussion to a large control group over a season. The authors found that a player with a concussion was more likely to have a greater exposure to head impacts on the day of concussion or season leading up to the concussion when compared to matched peers. The authors suggested that there may be a window of vulnerability and/or a time when concussion tolerance is low. This vulnerable window increases a player’s risk of concussion when exposed to a head impact; however, further research will be necessary to validate this finding. This will be particularly important to determine if the risk of concussion per head impact changes as a person is exposed to more impacts or if the current findings just show that the more times a head is impacted the more times there is a chance for concussion. It was also interesting to note that there were many high magnitude head impacts sustained by the control group, which suggests that finding a concussion threshold will be difficult. Researchers and medical professionals may need to re-assess the way head impact forces are used to assist in the identification of a potentially concussed athlete. Currently, medical professionals should be aware of the potential increased risk of injury an athlete may have due to repetitive head impacts. They should discuss with parents, coaches, and athletes the benefits of reducing head impact exposure through limiting contact practices.
Questions for Discussion: Should we consider limited contact practices not just in football but other sports as well (e.g., lacrosse, rugby, ice hockey)? Do you think we should still try and find a head impact threshold?
Written by: Jane McDevitt
Reviewed by: Jeffrey Driban
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This is definitely a very interesting article, I've never thought about the number of head impacts leading up to a concussion having an impact on vulnerability. I'm very interested to see where the research goes from here to see if there really is a benefit in trying to limit the amount of contact in certain sports to reduce the number of head impacts.
I'm sure it would be difficult to find and would take a lot of research, but I would also like to see if this leads to further investigation into how much force it actually takes to cause a concussion. I think determining this would really help in the future with developing better equipment that helps players from reaching that amount of force
Maybe I'm misinterpreting this, but couldn't this data simply suggest that those athletes that experience the most contact have the highest risk of concussion? As the have more exposures, it follows that they would have more concussions. This does not seem to suggest that repetitive impact in isolation increases risk of concussion.
Jacob,
I do think it was the authors intent with this article to measure the linear and acceleration forces that the brain can withstand, and at what force threshold would be the indicator for a concussion. However, I think the ranges athletes can withstand and other factors make it very difficult to measure. For example, how can we tweeze out who was ready for impact and who was not. If you were ready for impact you can activate neck musculature that would lessen the amount of shaking/whiplash the impact would have. I am not sure if there will be any piece of equipment that will prevent the brain shaking within the skull, but it would be nice to have an indicator to try and take the subjectivity out of initial diagnosis. Currently, if ATs do not see the impact and pull the athlete out to check then it is up to the athlete to identify if they are suffering from a potential concussion.
David,
Good point, I agree this data could just state that more exposure to impacts more risk of concussion.