Laird Harrison

April 09, 2014

SAN FRANCISCO — The more hits a football player's head takes during a season, the more changes show up on MRI of the player's brain, even in the absence of concussion, a new study shows.

Researchers used data from helmet sensors to estimate the risks associated with all impacts to the head sustained by 24 young players during a season, then compared these risks to the white matter changes in the players' brain visible by diffusion tensor imaging. They found a very close correlation.

"We all kind of took a step back and said, 'Wow,'" said Alexander Powers, MD, an assistant professor of neurosurgery at Wake Forest Baptist Medical Center in Winston-Salem, North Carolina.

Dr. Powers presented their findings here at the American Association of Neurological Surgeons (AANS) 82nd Annual Meeting.

Brain Development

In recent years, reports that many professional US football players have chronic traumatic encephalitis have raised concerns about the game. The worry has led to recent rule changes aimed at reducing the likelihood of head and neck injuries at all levels of the sport.

However, few researchers have evaluated the effects of the game on young athletes, although millions of children and teenagers play football at ages when their brains are undergoing sensitive development.

Dr. Powers and his colleagues performed MRI on the brains of 19 Jr. Pee Wee, 17 Pee Wee, and 40 high school players before the football season. They used diffusion tensor imaging, a refinement of MRI particularly sensitive to changes in white matter.

Then they placed Head Impact Telemetry System (HITS) sensors in the players' helmets and measured impacts over the course of games and practices for 1 complete season.

They reasoned that hits can vary in their effects depending on whether the acceleration is linear or rotational and on other factors. They estimated the probability and seriousness of the harmful effects caused by the impacts they recorded, creating a measurement of "risk-weighted cumulative exposure" (RWE).

Players who had the most hits were not necessarily the players who had the highest RWEs.

The researchers eliminated 2 players who had concussions from the study because they were interested in measuring the effects of impacts that did not cause concussion.

At the end of the season, they scanned the players' brains again. They found statistically significant correlations between changes in players' white matter and their RWE.

For example, they found an r2 of 0.4949 for the relationship of fractional anisotropy to RWE, which was statistically significant (P = .0001). The relationship was hardly changed by adjustment for age, body mass index, and the time between scans.

"Similar brain MRI changes have been previously associated with mild traumatic brain injury," said Dr. Powers.

Contribution to Understanding

In comments on the study during the AANS session, John E. Bailes, MD, from the University of Chicago Pritzker School of Medicine in Illinois, said the statistical power of the study was limited by its small number of participants.

"Also they use the HITS system, which has been under criticism for its accuracy," he said.

However, the study contributes to understanding of the relationship of brain trauma and football by pointing out the importance of impacts that don't result in concussion, he said. This could lead to helpful changes in practice styles, rules, and playing techniques to improve safety, said Dr. Bailes.

Neither Dr. Powers nor Dr. Bailes has disclosed any relevant financial relationships.

American Association of Neurological Surgeons (AANS) 82nd Annual Meeting. Abstract 702. Presented April 8, 2014.


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