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