Elsevier

Journal of Biomechanics

Volume 45, Issue 7, 30 April 2012, Pages 1265-1272
Journal of Biomechanics

Biomechanical correlates of symptomatic and asymptomatic neurophysiological impairment in high school football

https://doi.org/10.1016/j.jbiomech.2012.01.034Get rights and content

Abstract

Concussion is a growing public health issue in the United States, and chronic traumatic encephalopathy (CTE) is the chief long-term concern linked to repeated concussions. Recently, attention has shifted toward subconcussive blows and the role they may play in the development of CTE. We recruited a cohort of high school football players for two seasons of observation. Acceleration sensors were placed in the helmets, and all contact activity was monitored. Pre-season computer-based neuropsychological tests and functional magnetic resonance imaging (fMRI) tests were also obtained in order to assess cognitive and neurophysiological health. In-season follow-up scans were then obtained both from individuals who had sustained a clinically-diagnosed concussion and those who had not. These changes were then related through stepwise regression to history of blows recorded throughout the football season up to the date of the scan. In addition to those subjects who had sustained a concussion, a substantial portion of our cohort who did not sustain concussions showed significant neurophysiological changes. Stepwise regression indicated significant relationships between the number of blows sustained by a subject and the ensuing neurophysiological change. Our findings reinforce the hypothesis that the effects of repetitive blows to the head are cumulative and that repeated exposure to subconcussive blows is connected to pathologically altered neurophysiology.

Introduction

An estimated 3.8 million sports-related traumatic brain injuries (TBIs) occur in the United States every year (Langlois et al., 2006), many of which are concussions (Gessel et al., 2007). Repeated concussions have been linked to early-onset Alzheimer's disease (Guskiewicz et al., 2005), depression (McCrory et al., 2009), dementia (Guskiewicz et al., 2005), and chronic traumatic encephalopathy (McKee et al., 2009). Currently the medical cost of TBI in the United States is approximately $60 billion per year without considering the increase in TBI associated with recent military conflicts. Yet despite the prevalence of concussions and the serious long-term consequences, the link between the injury biomechanics and the ensuing pathophysiology remains poorly characterized (Goldsmith and Monson, 2005, McCrory et al., 2001).

Talavage et al. (2010) recently reported observation of neurophysiological changes in high school football players without observable symptoms of concussion. The reported finding of degraded neurological performance in the absence of classical symptoms of concussion is consistent with prior observation of chronic traumatic encephalopathy (CTE) in the absence of history of concussion in three ex-NFL players, as reported in (Field Hearing: Legal Issues Relating to Football Head Injuries, 2010, Omalu et al., 2005, Omalu et al., 2010). More recent discussion in the neuropathology community has implicated repetitive sub-concussive events as a significant source of accrued damage (Field Hearing: Legal Issues Relating to Football Head Injuries, 2010, McKee et al., 2009).

With the challenges of neural injury detection and the potential consequences if TBI goes unrecognized, it is critical that scientists, engineers, and medical professionals develop a better understanding of the mechanical events that lead to neurophysiological changes, how those events may accumulate over time, and how this accumulation affects healing processes. Toward this goal, neurophysiological changes and the biomechanical history of a cohort of high school football athletes were tracked for two seasons using instrumented helmets, functional magnetic resonance imaging (fMRI), and computer-based neuropsychological testing. This study expands upon our previous work (Talavage et al., 2010) by examining how the head collision histories of the athletes correlate with the observed changes in their neurophysiology, with the hypothesis being that the number and location of blows is directly correlated to the neurophysiological changes exhibited by the athlete.

Section snippets

Methods

All research methods were approved by an Institutional Review Board prior to the initiation of the study. Parental consent and participant assent were obtained from all subjects. The study is still ongoing, and the data reported here represents the aggregate data from two football seasons (2009 and 2010) (Talavage et al., 2010). In brief, the study consists of a cohort of high school football athletes for whom a neurophysiological and neuropsychological baseline was established in the

Results

There was no significant difference in the median peak linear acceleration for any of the three groups (Kruskal–Wallis, χ2=1.28, p>0.52, Fig. 1 and Table 2); however, a significant difference in the median total number of blows was found (Kruskal–Wallis, χ2=6.1, p<0.05, Table 2). Subsequent pairwise tests indicated that the COI−/FOI+ group sustained more blows than the COI−/FOI− group (Tukey–Kramer, p<0.05).

The number of side blows sustained by each of the groups (Fig. 2) was significantly

Discussion

The purpose of this study was to characterize the magnitude, location, and number of blows sustained by athletes participating in high school football and to establish correlations between these blows and ensuing changes in neurophysiology. According to Talavage et al. (2010), three distinct impairment groups are observable among high school football athletes: those with clinically observed impairment and functional impairment as measured by fMRI and neuropsychological testing (COI+/FOI+),

Conflict of interest statament

The authors declare that they have no financial interest in this study or its outcomes.

Acknowledgments

This work was supported by grants from the Indiana State Department of Health Spinal Cord and Brain Injury Research Fund, General Electric Healthcare, and through the National Science Foundation and National Defense Science and Engineering Graduate Fellowships. The authors thank Jeff Clevenger for his assistance in collecting helmet telemetry data and coordinating weekly battery changes. Finally, the authors thank Dr. Gregory G. Tamer, Jr., and Dr. Ruwan D. Ranaweera for their assistance with

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    Sources of Support: Indiana State Department of Health Spinal Cord and Brain Injury Research Fund; General Electric Healthcare; The National Defense Science & Engineering Graduate Fellowship (NDSEG) Program.

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