Sub-Concussive Hits: A Growing Concern in Youth Sports

Cause for concern

Since publication of the Purdue study, similar findings have been made by researchers at the University of Rochester Medical Center (URMC) (8). In measuring before-and-after data from the brains of a group of nine high school football and hockey players using diffusion tensor imaging (DTI), researchers found subtle evidence of axonal injury at the cellular level among six of athletes who were not diagnosed with concussion but sustained many sub-concussive blows during the normal course of play.  The abnormalities disclosed on post-season DTI scans among the players were closer to the the scan of the one player with diagnosed concussion than to the normal brains in the control group. Axons, which are like cables woven throughout brain tissue, swell up when traumatic brain injury occurs.

The imaging changes also strongly correlated with the number of head hits (self-reported by the athletes in a diary), the symptoms experienced, and independent cognitive tests, said lead author Jeffrey Bazarian, M.D., M.P.H., associate professor of Emergency Medicine at URMC. 

A 2013 study by researchers at URMC and the Cleveland Clinic (9) also found evidence of brain damage in college football players from sub-concussive hits in the form of elevated levels of a protein in the blood usually present only in the brain. The presence of the S100B protein triggers the release by the body of antibodies which can then leak back into the brain through the damaged blood-brain barrier, where they are thought to attack brain tissue.  The highest protein levels were found among players who sustained the most hits to the head during games and practices.   

The findings in the Rochester and Purdue studies support anecdotal evidence from other studies that football players not diagnosed with concussions nevertheless seem to suffer cognitive impairment. In other words, some players are injured, but don't know it (unlike players who know they are experiencing concussion symptoms but who, for a variety of reasons, fail to report such symptoms, which continues to be a chronic problem). 

The findings are troubling, says Larry J. Leverenz, PhD, ATC, of the Department of Health and Kinesiology at Purdue, because the players:

1. Escape detection.  Because they have not suffered damage to areas of the brain associated with language and auditory processing, they are unlikely to exhibit clinical signs of head injury (such as headache or dizziness), or show impairment on sideline assessment for concussion, all of which test for verbal, not visual memory, so "there is no way right now to identify" the group suffering sub-concussive blows to the head that may be dangerous.  Hence, they will likely continue participating in football-related activities, even when changes in brain physiology are present, which studies show likely increases the risk of future neurologic injury;
2. Don't know they are injured.  If working memory deficits are sufficiently small, a player may not be aware of the additional effort required to complete everyday tasks, and therefore not think to bring the problem to anyone's attention (although at least one of the players in the impaired group seemed to have figured this out, and played with better, heads-up technique the next season, reducing the number of hits he took to the forehead); and
3. Face an uncertain future.  Even though the players in the Purdue study who suffered short-term cognitive impairment from repeated sub-concussive blows exhibited results on fMRI and ImPACT tests administered before season #2 comparable to the baseline results before season #1, their return to baseline does not necessarily mean that there was 100% recovery.  It is possible that the damage will only be known over the long term, years later.

Commenting on the Purdue study for Sports Illustrated, Randall Benson, a neurologist at Wayne State University in Detroit, suggested that the Purdue researchers may have taken what amounted to a "real-time snapshot" of the early stages of the corrosive creep that wears away at the frontal lobe, a part of the brain involved in navigating social situations. Too much erosion and victims reach a breaking point - like former Steelers offensive lineman Terry Long, who died in 2005 from drinking antifreeze. "It's an insidious progression," Benson said, "and it's not obvious when you talk to [players]."

Is better detection the answer?

One approach to the problem of sub-concussive blows that escape detection via conventional means is to find new enhanced detection methods: If functional impairment could be detected on the sports sideline, a player, like those exhibiting more obvious concussion signs or complaining of symptoms consistent with concussion, could be removed from play.

As Dr. Leverenz noted, the problem with sideline assessment tools in current use, such as the Standardized Assessment of Concussion (SAC) and the Sports Concussion Assessment Tool 2 (SCAT2), is that they test verbal memory, not the visual memory that he and the Purdue researchers found impaired in the functionally, but not clinically impaired, players who experienced at least short-term neurologic trauma from repeated, sub-concussive hits to the head.

All too often, even hits hard enough to cause an athlete to experience signs of concussion that can be observed by sideline personnel, or which cause the athlete to experience symptoms of concussion, go undetected, either because the signs are simply missed by sideline personnel or because the athlete fails to report them (a 2010 study⁷ of Canadian junior hockey players, for example, found that, for every concussion self-reported by the players or identified by the coaches or on-the-bench medical personnel, physician observers in the stands picked up seven) - a persistent problem that, given the "warrior" mentality and culture of contact and collision sports, is not going to go away any time soon, if ever. 

One way to increase the chances of detection is to install sensors in players' helmets or mouth guards to alert sideline personnel to head impact exposure, either from a single, forceful hit, or from less forceful but repetitive blows, that has the potential to result in brain injury, which helps to identify athletes who should be removed for evaluation on the sports sideline and, if found to have a suspected brain injury, referred for further evaluation and banned from a return to play.⁶ 

Hit limits 

But better detection does nothing to prevent such brain trauma, or at least reduce the risk, in the first place.  No matter how good the technology, no matter how good we get at identifying suspected concussions, the essential problem remains: the hits themselves. 

As a result, experts say, the focus must be on reducing the risk of concussions and sub-concussive brain trauma by reducing exposure to concussive and sub-concussive hits that athletes sustain during contact and collision sports.  

"The challenge," said Bazarian, the author of the Rochester study,⁸ "is to determine whether a critical number of head hits exists above which this type of brain injury appears, and then to get players and coaches to agree to limit play when an athlete approached that number."  

1. Talavage T, Nauman E, Breedlove E, et. al. Functionally-Detected Cognitive Impairment in High School Football Players Without Clinically-Diagnosed Concussion. J Neurotrauma. 2010; DOI: 10.1089/neu.2010.1512.

2.  Crisco JJ, Fiore R, Beckwith JG, et al. Frequency and location of head impact exposures in individual collegiate football players. J. Athl Train 2010;45:549-559.

3. Field M, Collins MW, Lovell MR, Maroon J. Does age play a role in recovery from sports related concussion? A comparison of high school and collegiate athletes. J Pediatr. 2003;414:546-553.

4. Pullela R, Raber J, Pfankuch T. et al. Traumatic injury to the immature brain results in progressive neuronal loss, hyperactivity and delayed cognitive impairments. Dev Neurosci 2006;28:396-409.

5. Stern R, Riley D, Daneshvar D, Nowinski C, Cantu R, McKee A. Long-term Consequences of Repetitive Brain Trauma: Chronic Traumatic Encephalopathy. Phys. Med. & Rehab. 2011;3;S460-S467. DOI:10.1016/j.pmrj.2011.08.008.

6. Greenwald R, Chu J, Beckwith J, Crisco J. A Proposed Method to Reduce Underreporting of Brain Injury in Sports. Clin J Sport Med 2012; 22(2):83-85.

7. Echlin P, Tator C, et al. A prospective study of physician-observed concussions during junior ice hockey: implications for incidence rates.  Neurosurg Focus 2010;29(5):E4.

8. Bazarian JJ, Zhu T, Blyth B, Borrino A, Zhong J.  Subject-specific changes in brain white matter in diffusion tensor imaging after sports-related concussion.  Magnetic Resources Imaging. 2012; 30(2): 171-180.

9. March N, Bazarian JJ, Puvenna V, Janigro M, Ghosh C, et. al. Consequences of Repeated Blood-Brain Barrier Disruption in Football Players. PLoS ONE 2013;8(3): e56805. doi: 10.1371/journal.pone.0056805.  

Posted April 6, 2012; most recently revised March 11, 2013