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Six Degree-of-Freedom Measurements of Human Mild Traumatic Brain Injury

An Erratum to this article was published on 30 October 2015


This preliminary study investigated whether direct measurement of head rotation improves prediction of mild traumatic brain injury (mTBI). Although many studies have implicated rotation as a primary cause of mTBI, regulatory safety standards use 3 degree-of-freedom (3DOF) translation-only kinematic criteria to predict injury. Direct 6DOF measurements of human head rotation (3DOF) and translation (3DOF) have not been previously available to examine whether additional DOFs improve injury prediction. We measured head impacts in American football, boxing, and mixed martial arts using 6DOF instrumented mouthguards, and predicted clinician-diagnosed injury using 12 existing kinematic criteria and 6 existing brain finite element (FE) criteria. Among 513 measured impacts were the first two 6DOF measurements of clinically diagnosed mTBI. For this dataset, 6DOF criteria were the most predictive of injury, more than 3DOF translation-only and 3DOF rotation-only criteria. Peak principal strain in the corpus callosum, a 6DOF FE criteria, was the strongest predictor, followed by two criteria that included rotation measurements, peak rotational acceleration magnitude and Head Impact Power (HIP). These results suggest head rotation measurements may improve injury prediction. However, more 6DOF data is needed to confirm this evaluation of existing injury criteria, and to develop new criteria that considers directional sensitivity to injury.

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We thank the Stanford Department of Athletics (Palo Alto, CA) for enabling this research, notably Scott Anderson, Director of Athletic Training, and Mike Gleeson, Video Director. We thank Kevin Bui and Bradley Hammoor for work in processing the event video, Joseph Schooler for coordinating human subject protocols, and Maria Malone for device manufacturing and deployment. We thank X2 Biosystems (Seattle, WA) for early device prototypes and continual support. We thank Roy Englebrecht Promotions (Newport Beach, CA) and B Street Boxing (San Mateo, CA) for help with subject recruitment. The study was supported by the National Institutes of Health (NIH) National Institute of Biomedical Imaging and Bioengineering (NIBIB) 3R21EB01761101S1, David and Lucile Packard Foundation 38454, Child Health Research Institute of Stanford University, and NIH UL1 TR000093 for biostatistics consultation.

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None of the authors had any conflict of interest regarding this manuscript.

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Correspondence to David B. Camarillo.

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Associate Editor Joel D. Stitzel oversaw the review of this article.

Electronic supplementary material


Supplemental Fig. 1. Distribution of 6DOF head impact measurements by sport. Kinematics histograms were plotted for the non-injury American football, boxing, and mixed martial arts head impacts. The distributions of each sport were similar for all measures. In the left-right and coronal directions, the LOC injury was very high percentile. For the other directions, the LOC injury was less distinguishable from non-injury. The self-reported injury was generally less distinguishable than the LOC injury. (PDF 22 kb)


Supplemental Fig. 2. Distribution of head impact acceleration directions. Rotational histograms of head impacts are plotted in each plane for maximum translational acceleration (), and maximum rotational acceleration (B). Head impacts occurred over a broad spectrum of directions. In each plane, the injuries lie in directions where only a small percentage of noninjuries occurred, supporting the use of multidimensional analysis to helps distinguish injury from non-injury. (PDF 33 kb)

Supplemental Movie 1. Video of American football mTBI impact. Video of the head impact was recorded at 40 frames s−1 and is compared to an animation of the device recordings. Time synchronized measurements of translational acceleration and angular acceleration are shown below. (MOV 9403 kb)

Supplemental Movie 2. Video of a mixed martial arts non-injury head impact. Video of the head impact was recorded at 1300 frames s−1 and is compared to an animation of the device recordings. Time synchronized measurements of translational acceleration and angular acceleration are shown below. (MOV 9280 kb)

Supplemental Movie 3. Simulation of brain during loss of consciousness (LOC). A finite element simulation of an LOC head impact (Methods) reveals maximum tensile strain of 30% occurs at t = 30 ms in the corpus callosum and brainstem. Damage to these regions is thought to affect perception and consciousness. Sagittal and coronal views of the brain are provided in the video. (MOV 20295 kb)

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Hernandez, F., Wu, L.C., Yip, M.C. et al. Six Degree-of-Freedom Measurements of Human Mild Traumatic Brain Injury. Ann Biomed Eng 43, 1918–1934 (2015).

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  • Concussion
  • Mild traumatic brain injury (mTBI)
  • Instrumented mouthguard
  • Six degree-of-freedom (6DOF) kinematics
  • Finite element model
  • Brain strain