Editorial: Subconcussion in traumatic brain injury

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Recent scientific data and news stories in the lay press have challenged our ideas of how blows to the head in contact sports are diagnosed and treated. The classically held belief that concussed players can return to play as soon as they've regained their senses has given way to concepts such as “second impact syndrome” and “cognitive exertion.” Indeed, there is mounting evidence that mild brain trauma can result in changes in neural function and vascular reactivity far more extensive and long lasting than previously thought. Players suffering a concussion are now subject to much greater scrutiny by coaches, trainers, and medical staff. They must now undergo extensive neuropsychological test batteries, sideline tests, and detailed medical assessments before being allowed to return to the field of play. This is clearly to the player's benefit and makes contact sports a safer venture for these athletes.

Another issue associated with sports-related concussions is the topic in the following paper by Bailes et al., who begin with an examination of what constitutes a meaningful head injury.1 With current efforts aimed at reducing morbidity following concussion per se, it is theoretically possible that milder forms of head injury could have a deleterious effect on players, unrecognized under current criteria. These so-called subconcussive injuries are a bit tougher to accurately define. Not every incidental blow to the head is pathological. Bailes and colleagues define these injuries as cranial impacts or acceleration/deceleration injuries that do not result in a clinically diagnosed concussion. They argue that it is the cumulative effect of these smaller blows that can cause neurological dysfunction. They review the pertinent laboratory and clinical evidence, arguing that subclinical impacts to the head should not be ignored in our efforts to make contact sports safer and that the number of such impacts should be tracked and minimized. This, of course, is a tall order. The impacts are extremely difficult to quantify, and not every subconcussive injury has the same significance. Is a soccer “header” of the same import as a nonconcussive blow to the head in a football game? Indeed, is every soccer header to be considered the same, or does a change in angular acceleration of the head make a difference in how significant this is from a subconcussive standpoint? We already face significant challenges in trying to keep track of actual concussive injuries in contact sports; tracking those events resulting in subconcussive forces is likely to be truly formidable. Moreover, the notion that the mere number of these events is the most important determining factor of long-term injury vastly oversimplifies matters; it is likely that there are genetic differences in the players themselves, placing certain individuals at higher risk of long-term neurological dysfunction than others. Still, the concept of repetitive subconcussive brain injury is an important one. Efforts to get a better handle on the number, types, and degrees of severity of these injuries will go a long way to improving our understanding and protecting our young players from long-term harm. Bailes and colleagues are to be commended for focusing our attention and providing the readership with a thoughtful synthesis of current evidence on this problem.

Disclosure

The author reports no conflict of interest.

Reference

1

Bailes JEPetraglia ALOmalu BINauman ETalavage T: Role of subconcussion in repetitive mild traumatic brain injury. A review. J Neurosurg [epub ahead of print August 23 2013. DOI: 10.3171/2013.7.JNS121822]

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We appreciate Dr. Sagher's comments regarding our report on subconcussive impacts in contact sports. We agree with his points that identifying and tracking subconcussive impacts are difficult and that there is uncertainty in what potential each blow may represent in terms of brain injury at the cellular or ultrastructural level. Although our knowledge of sports concussions has grown during the last decade, it was initially counterintuitive that anyone who did not have a history replete with diagnosed concussions could possibly have the potential for cumulative or chronic degenerative disease processes of the brain. Research that has emerged during that time, both in the clinical realm and through laboratory investigation, supports the notion that deleterious effects may, in a minority of individuals, accrue without the presence of known concussions.

We believe that Dr. Sagher is correct in that there are probably genetic factors, such as polymorphisms in apolipoprotein E and interleukin-6, among others, that will play an important role in the susceptibility to and recovery from injury. Interestingly, studies by Breedlove et al.1 and Talavage et al.,2 which included preseason assessments and in-season monitoring of head impacts and brain function, revealed that only the number and location of hits predict neurophysiological changes. At first glance, these findings support the idea that brain tissue fatigues or becomes susceptible during repetitive impacts—like the rotator cuff in baseball pitchers. It suggests that there may be a number of hits per season or throughout a career that is relatively safe. As these kinds of data sets expand, however, it is likely that we will be able to determine the hits that cause damage or, more importantly, the magnitudes that do not cause damage. The latter finding would be extraordinarily useful because it could provide design criteria for helmets and other protective equipment.

Overall, the objective in our report was to describe our and others' research that points out this potential phenomenon and the differences between concussion and other cranial hits that could, given the right circumstances, result in subacute or chronic detrimental brain effects. As more advanced technology becomes available, reliable, and affordable, we may be able to measure applied forces, along with other biometrics, constituting a “smart helmet” concept. Rather than continuously reacting to injuries and their sequelae, it may become advantageous for the caretakers' plan of care to be more proactive. We believe that the existing science is more than theoretical, and it is hard to imagine that total career or lifetime exposure is not going to become a meaningful and perhaps actionable number for those who experience thousands of blows to the head in the course of sports participation. Future research will tell if preventative strategies, such as limiting exposure, will help to ensure that even minor subclinical injury is not detrimental.

References

  • 1

    Breedlove ELRobinson MTalavage TMMorigaki KEYoruk UO'Keefe K: Biomechanical correlates of symptomatic and asymptomatic neurophysiological impairment in high school football. J Biomech 45:126512722012

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  • 2

    Talavage TMNauman EBreedlove ELYoruk UDye AEMorigaki K: Functionally-detected cognitive impairment in high school football players without clinically-diagnosed concussion. J Neurotrauma [epub ahead of print]2013

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Article Information

Please include this information when citing this paper: published online August 23, 2013; DOI: 10.3171/2013.4.JNS13538.

© AANS, except where prohibited by US copyright law.

Headings

References

  • 1

    Bailes JEPetraglia ALOmalu BINauman ETalavage T: Role of subconcussion in repetitive mild traumatic brain injury. A review. J Neurosurg [epub ahead of print August 23 2013. DOI: 10.3171/2013.7.JNS121822]

    • Search Google Scholar
    • Export Citation
  • 1

    Breedlove ELRobinson MTalavage TMMorigaki KEYoruk UO'Keefe K: Biomechanical correlates of symptomatic and asymptomatic neurophysiological impairment in high school football. J Biomech 45:126512722012

    • Search Google Scholar
    • Export Citation
  • 2

    Talavage TMNauman EBreedlove ELYoruk UDye AEMorigaki K: Functionally-detected cognitive impairment in high school football players without clinically-diagnosed concussion. J Neurotrauma [epub ahead of print]2013

    • Search Google Scholar
    • Export Citation

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