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
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
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 increase 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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