Although current events in professional sports have highlighted the concerns of traumatic brain injury in athletes, clinical and scientific studies that guide decisions at the collegiate and professional levels are not directly translatable to the pediatric population. Also, the decisions about whether any concussion has occurred or the safety of a player to “return to play” are rarely guided by clinicians in the pediatric population. And the existing data about the effects of mild head injury and repeated head injury in the developing brain is difficult to investigate. There is a paucity of this information due to most animal models of head injury leading to significant mortality, requiring craniotomies, and employing younger animals. With growing information about postnatal neurogenesis in the mammalian brain, the ability to interrogate the effects of repeated head injury in the context of neurodevelopmental biology would provide valuable insights.
A recent article by Prins et al (Dev Neurosci Sept, 2010) created a closed head injury model for postnatal day-35 rats; single and repeat traumatic brain injury (1-day interval) were examined histologically for axonal injury and behaviorally by the novel object recognition task. The results from the current study demonstrate that an experimental closed head injury in the rodent with low mortality rates and absence of gross pathology can produce measurable cognitive deficits in a juvenile age group. The introduction of a second injury 24 hours after the first impact resulted in increased axonal injury, astrocytic reactivity, and increased memory impairment in the novel object recognition task [Figure 6 from the original paper].
Strong evidence exists regarding the risk of repeated traumatic brain injury and the acute risks of malignant cerebral edema as well as long term risks for neurodegenerative diseases and encephalopathy. Accordingly, strict guidelines have gradually become a prominent part of professional football as demonstrated by the National Football League's placement of posters in each locker room warning of the risks from repeated head injury. This also has been effectively implemented by greater influence of trainers as well as new changes in permissible tackling styles. Yet most concussions and subclinical head injury in sports occurs at the pediatric level which resides at the uniquely challenging intersection of no clinical supervision and the developing brain. Information guiding decisions on risks to the pediatric athletic population will most likely arise from preclinical data; specifically data on the “window of vulnerability” should improve the guidelines for children, who can continue to benefit from the value of athletic competition with reduced risk for neuropsychiatric injury.
Matthew J. Duenas