Post Concussion cognitive declines and symptomatology are not related to concussion biomechanics in high school football players
Broglio SP, Eckner JT, Surma T, Kutcher JS. J Neurotrauma. 2011 Jun 6. [Epub ahead of print].
One of the most elusive quantities in brain injury research is the “kinematic threshold”. Kinematics is the description of motion using variables like linear and angular displacement, velocity, and acceleration. For many years researchers have tried to identify the amount of linear or angular head impact acceleration that, if exceeded, would indicate a concussive event. This proposed threshold has been reported as low as 60 to 80 gravitational units (g) for concussion and 200 g for severe brain injury. This would be a nice value to know as we try to create equipment and modify playing techniques to avoid this head kinematic threshold. One problem is that concussions are the result of many variables including impact location, magnitude, direction, injury history, gender, and impact history. This well performed study is unique in that the authors used the Head Impact Telemetry System to evaluate the relationship between head impact mechanics (i.e., time between session start and injury, time since the previous impact, linear acceleration, rotational acceleration, and severity profile, number of impacts) before and after the concussion occurrence on amount of clinical signs and symptoms (including cognitive performance). The authors evaluated 19 high school football athletes who sustained 20 diagnosed concussions over four seasons. Similar to previous research, there was no relationship between the kinematic measures and the concussion signs and symptoms.
As the authors note, this is interesting because the current results contradict the prevailing wisdom that the greater the head impact kinematics (i.e., linear or angular accelerations), the poorer the outcome (e.g., greater concussive symptoms). Is the size of the hit or number of hits not related to outcome? To be determined… Data analyses with more concussions may aid in answering this question. In the end, I think what this and previous evidence is telling us is that each athlete should be evaluated on an individual basis. That is, two players may react differently following similar impacts and clinicians should be on guard for brain injury not just based on the size of the hit, but also the player’s age, experience, injury history, size, gender, etc. In other words: use your judgment and instincts and be proactive in your sideline assessment.
Written by: Ryan Tierney
Reviewed by: Jeffrey Driban