Measuring Head Kinematics in Football: Correlation Between the Head Impact Telemetry System and Hybrid III Headform
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Over the last decade, advances in technology have enabled researchers to evaluate concussion biomechanics through measurement of head impacts sustained during play using two primary methods: (1) laboratory reconstruction of open-field head contact, and (2) instrumented helmets. The purpose of this study was to correlate measures of head kinematics recorded by the Head Impact Telemetry (HIT) System (Simbex, NH) with those obtained from a Hybrid III (HIII) anthropometric headform under conditions that mimicked impacts occurring in the NFL. Linear regression analysis was performed to correlate peak linear acceleration, peak rotational acceleration, Gadd Severity Index (GSI), and Head Injury Criterion (HIC15) obtained from the instrumented helmet and HIII. The average absolute location error between instrumented helmet impact location and the direction of HIII head linear acceleration were also calculated. The HIT System overestimated Hybrid III peak linear acceleration by 0.9% and underestimated peak rotational acceleration by 6.1% for impact sites and velocities previously identified by the NFL as occurring during play. Acceleration measures for all impacts were correlated; however, linear was higher (r 2 = 0.903) than rotational (r 2 = 0.528) primarily due to lower HIT System rotational acceleration estimates at the frontal facemask test site. Severity measures GSI and HIC were also found to be correlated, albeit less than peak linear acceleration, with the overall difference between the two systems being less than 6.1% for either measure. Mean absolute impact location difference between systems was 31.2 ± 46.3° (approximately 0.038 ± 0.050 m), which was less than the diameter of the impactor surface in the test. In instances of severe helmet deflection (2.54–7.62 cm off the head), the instrumented helmet accurately measured impact location but overpredicted all severity metrics recorded by the HIII. Results from this study indicate that measurements from the two methods of study are correlated and provide a link that can be used to better interpret findings from future study using either technology.
KeywordsHead impact Concussion Biomechanics Football
The authors gratefully acknowledge the funding for this study provided by the National Institutes of Health (R01HD048638). HIT System technology described in this study was developed with support from the National Institutes of Health (R44HD40743 and R01HD048638) and from Riddell, Inc. (Chicago, IL). Helmets and associated hardware were also provided by Riddell, Inc. The study protocol was developed in conjunction with the National Football League’s Committee on Mild Traumatic Brain Injury, which provided funding to Biokinetics to operate the linear impactor. Following data collection at the said facility, data from both systems were mutually exchanged. Additional Contributions: David Viano, as co-chairman of the NFL’s mTBI Committee at the time of this data collection, approved the initial protocol and funding to Biokinetics, but he did not participate in data collection, analysis, or interpretation of the data. At his request, following primary data collection and analysis by Simbex and Biokinetics, impact sites A′ and A′′ were added to the test protocol. These data were collected 7 months after the initial testing. The interpretation of the material presented within this communication is solely that of the authors and not necessarily reflective of the sponsor’s views. The authors would like to thank Mr. Chris Withnall and Mr. Michael Wonnacott from Biokinetics and Associates, Ltd who provided technical expertise when needed and assisted with data collection. In addition, the authors would like to thank Joseph Crisco from Brown University for assisting with data interpretation.
Conflict of Interest
Jonathan Beckwith, Jeffrey Chu and Richard Greenwald, as employees or as beneficial owner of Simbex, have a financial interest in the HIT System technology used in this study.
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