Sports Medicine Research: In the Lab & In the Field: Concussive Threshold: TBD? (Sports Med Res)
Monday, April 29, 2013

Concussive Threshold: TBD?

Head impact exposure sustained by football players on days of diagnosed concussion

Beckwith J.G., Greenwald R.M., Chu J.J., Crisco J.J., Rowson S., Duma S.M., Broglio S.M., McCallister T.W., Guskiewicz K.M., Mihalik J.P., Anderson S., Schnebel B., Brolinson P.G., Collins M.W. Medicine and Science in Sport and Exercise. 2013; 45: 737-746

Take Home Message: Players sustained more head impacts and higher severity of impacts on days of diagnosed concussion compared to days with no diagnosed concussion. Also, peak linear acceleration was the best predictor of immediately diagnosed concussions.

Concussion prevention methods are difficult to develop because we lack an understanding of the relationship between head impact mechanics and subsequent concussions. We can improve our understanding by measuring impact forces during sporting events; however; most studies have only included a small number of athletes, which limited the ability to determine which biomechanical characteristics result in injury among football athletes. Therefore, the purpose of this study was to compare frequency and kinematic response of head impacts on days with and without a diagnosis of concussion and identify sensitivity and specificity of single-impact severity measures to diagnose concussive injuries. Football players from 8 colleges and 6 high schools wore instrumented [Head Impact Telemetry (HIT) system] helmets, which recorded measures of head impact exposure (i.e., frequency, location, and kinematic response of head impacts) during a 6-year period. A total of 161,732 head impacts were recorded over 10,972 player days among 95 football athletes diagnosed with a concussion. This yielded 105 cases of diagnosed concussions (8 players sustained 2 concussions and 1 player sustained 3 concussions). Seventy percent of the concussions occurred during a game or scrimmage. In 45 concussion cases the players were removed immediately after injury and diagnosed with a concussion. In the remaining 60 cases the athletes continued to play, which resulted in a delayed diagnosis. Measurements from the HIT system were compared between days with and without diagnosed concussion. The authors found that the frequency and severity of head impacts were greater on days with diagnosed concussion compared to days with no concussion diagnosis. For cases that were immediately diagnosed with concussion after head impact the magnitude of peak head acceleration was the most sensitive factor in detecting concussions. Peak rotational acceleration was the least sensitive measure to detect a concussion compared to all other kinematic measures.

This was the largest collection of real-time biomechanical data from head impacts within an athletic population associated with the diagnosis of concussion. The key findings presented in this study indicate that players sustain both a greater number and severity of head impacts on days with diagnosed concussion compared to days with no diagnosed concussion. However, it is important to remember that these findings are primarily applicable to football players that are immediately diagnosed with a concussion since the authors excluded the 60 cases with a delayed diagnosis of concussion. Athletes with a delayed diagnosis are important because the authors previously found that this is the majority of concussions and the mechanism of their concussion is not as easy to identify. It was also interesting to note that rotational acceleration was found to be the least sensitive of all the severity measures to detect an immediately diagnosed concussion since previous research suggested that poorer outcomes come from a rotational injury rather than from linear impacts. Finally, kinematic measurements on days without a concussion were almost identical to previously reported measurements among football players that had no diagnosed concussion, which demonstrates the repeatability of this method to assess concussion.. Overall, this data may help us develop better prevention methods (e.g., equipment, rule changes) or eventually help clinicians detect athletes exposed to dangerous head impacts. Do you think a rule change would help decrease the number of concussions? Do you think having a concussion threshold will help diagnose some concussions?

Written by: Jane McDevitt MS, ATC, CSCS
Reviewed by: Jeffrey Driban

Related posts:
Beckwith JG, Greenwald RM, Chu JJ, Crisco JJ, Rowson S, Duma SM, Broglio SP, McAllister TW, Guskiewicz KM, Mihalik JP, Anderson S, Schnebel B, Brolinson PG, & Collins MW (2013). Head Impact Exposure Sustained by Football Players on Days of Diagnosed Concussion. Medicine and Science in Sports and Exercise, 45 (4), 737-746 PMID: 23135363

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