Biomechanical correlates of symptomatic and asymptomatic neurophysiological impairment in high school football.
Breedlove EL, Robinson M, Talavage TM, Morigaki KE, Yoruk U, O’Keefe K, King J, Leverenz LJ, Gilger JW, Nauman EA. J Biomech. 2012 Feb 28 [Epub ahead of print].
Perhaps we’ve been looking at it all wrong. Concussions may not just be the result of a single blow, but instead several subconcussive blows may lead to a concussion. Instead of looking at the magnitude of a single hit in search of a concussion “threshold,” research should begin to focus on the number and location of hits an athlete endures and their consequences. Breedlove et al recently did just this, while also trying to establish correlations between hits and changes in neurophysiology. Over 2 football seasons a cohort study was performed using high school athletes (21 athletes throughout season 1, 25 athletes throughout season 2, which included 14 from the first season). Prior to the start of the season, a neurophysiological and neuropsychological baseline was established for all subjects using ImPACT and functional magnetic resonance imaging (fMRI). These tests were also performed in-season, and post-season. Additionally, during the seasons, all participants’ head impacts were monitored using the Head Impact Telemetry (HITTM) System. The participants were divided into certain injury groups based on “clinically observed impairment” (COI, any signs and symptoms found by the clinician that would indicate a concussion) and “functionally-observed impairment” (FOI, any changes that were detected by neuropsychological testing and fMRI) standards. The authors identified a group with no clinical findings but positive FOI results. Furthermore the results showed this group sustained more blows to the head than the group with no clinical or functional impairments. The group with clinical and functional impairments, and the group with no clinical findings, but mixed functional results, had an association relating history of blows to structures of the basal ganglia, cerebellum, and limbic structures. This particular study also identified strain patterns resembling those, which have been believed to be a part of the biomechanical process that commences the sequelae of concussion.
One of the many reasons why this study is so interesting is that some of its findings correlate to previous research with chronic traumatic encephalopathy (CTE). In the past, neurodegeneration in the basal ganglia, cerebellum, and limbic structures has been found in patients with CTE. These structures are where most athletes in this study experienced the majority of their blows. Because of their function, degeneration in this location may be the cause of emotional and behavioral disorders found in those with CTE (McKee 2009). Furthermore, the lasting strain effects found within the subjects may contribute to mechanical fatigue. Introducing these involved structures, which may have not fully healed, to continued subconcussive blows, may be what causes the outward symptoms of concussion to occur. Because of their lasting effect, subconcussive blows may also lead to the development of CTE (McKee 2009), or at the very least signs of impaired brain function based on fMRI results in this study. So how long does the tissue of the brain take to recover from impacts? Future research should focus on the rate at which the brain heals from different and multiple blows, to determine accurate return to play guidelines. Overall, this study proposes insightful data including the observation that athletes lacking outward symptoms may still be experiencing functional deficits as demonstrated by fMRI. Based on this, should athletes, recovering from a concussion, be held out of play even after their physical symptoms have resolved and they have passed all exertional tests? Likewise, now understanding that multiple subconcussive blows may lead to a concussion, how should this affect current playing decisions; should athletes only be allowed to take a number of hits before being pulled from the field?
Written by: Jacqueline Phillips
Breedlove EL, Robinson M, Talavage TM, Morigaki KE, Yoruk U, O’Keefe K, King J, Leverenz LJ, Gilger JW, & Nauman EA (2012). Biomechanical correlates of symptomatic and asymptomatic neurophysiological impairment in high school football. Journal of biomechanics PMID: 22381736