Comparison of Head Impact Exposure Between Concussed Football Athletes and Matched Controls: Evidence for a Possible Second Mechanism of Sport-Related Concussion

Brian D Stemper,Alison Brooks,Stefan M Duma,Thomas W Mcallister,Steven J Svoboda,Gerald Mcginty ,Kenneth L Cameron,Darren E Campbell ,John P Difiori,Christopher C Giza,Jonathan Jackson,Kevin M Guskiewicz,Alok S Shah,Steven Rowson,Steven P Broglio,Jaroslaw Harezlak,Larry Riggen ,Jason P Mihalik,Michael Mccrea

doi:10.1007/s10439-018-02136-6

Abstract

Studies of football athletes have implicated repetitive head impact exposure in the onset of cognitive and brain structural changes, even in the absence of diagnosed concussion. Those studies imply accumulating damage from successive head impacts reduces tolerance and increases risk for concussion. Support for this premise is that biomechanics of head impacts resulting in concussion are often not remarkable when compared to impacts sustained by athletes without diagnosed concussion. Accordingly, this analysis quantified repetitive head impact exposure in a cohort of 50 concussed NCAA Division I FBS college football athletes compared to controls that were matched for team and position group. The analysis quantified the number of head impacts and risk weighted exposure both on the day of injury and for the season to the date of injury. 43% of concussed athletes had the most severe head impact exposure on the day of injury compared to their matched control group and 46% of concussed athletes had the most severe head impact exposure for the season to the date of injury compared to their matched control group. When accounting for date of injury or season to date of injury, 72% of all concussed athletes had the most or second most severe head impact exposure compared to their matched control group. These trends associating cumulative head impact exposure with concussion onset were stronger for athletes that participated in a greater number of contact activities. For example, 77% of athletes that participated in ten or more days of contact activities had greater head impact exposure than their matched control group. This unique analysis provided further evidence for the role of repetitive head impact exposure as a predisposing factor for the onset of concussion. The clinical implication of these findings supports contemporary trends of limiting head impact exposure for college football athletes during practice activities in an effort to also reduce risk of concussive injury.

Highlights

Sport-related concussion (SRC) has become increasingly recognized as a significant public health issue,54 known to produce acute changes in brain function resulting in an array of postconcussive symptoms and functional impairments
The present analysis identified the role of repetitive head impact exposure as a moderator for concussive injury in some college football athletes
Results of this study demonstrated consistency with regard to the severity of repetitive head impact exposure between injured athletes and controls, with acceleration magnitudes of routine (50% percentile) and higher magnitude (75th and 90th percentile) head impacts varying by 5% or less between the two groups

Summary

Introduction

Sport-related concussion (SRC) has become increasingly recognized as a significant public health issue, known to produce acute changes in brain function resulting in an array of postconcussive symptoms and functional impairments. It has long been understood that the biomechanical mechanism of concussion is associated with head impact resulting in linear and rotational accelerations.. To investigate concussion biomechanics in a sports setting, electronic sensor systems were developed to quantify head impact accelerations. The most commonly used system is the Head Impact Telemetry (HIT) System, which consists of a series of accelerometers placed between the padding gaps of Riddell football helmets.. The HIT System was used to quantify head impact biomechanics associated with concussion in football, resulting in the development of injury risk curves using regression techniques.. The implicit assumption of these analyses is that the biomechanical onset of concussion (i.e., the concussive injury) was associated with a single head impact event. The single impact mechanism of concussion is supported by a wealth of experimental studies.

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