June 15, 2021
Imaging shows even mild head impacts can have long-term neurological effects.
Repeated head impact exposure (HIE) over time can cause neurological changes in athletes who play contact sports even if the event doesn’t lead to a concussion.
In a study published Tuesday in the Journal of Neurosurgery: Pediatrics, investigators from Wake Forest School of Medicine and the University of Texas Southwestern in Dallas shared the results of their longitudinal study that showed concerns over sports-related head injuries – particular in football – are warranted.
Their findings reveal that the amount of HIE is positively associated with the change in a player’s neuroimaging metrics. Exposure did not need to be severe in order to cause a long-term impact. Overall, their work contributes to long-standing research efforts that have examined the lifelong impacts, including neurological degradation, of head injuries in contact sports.
“Our findings further support ongoing efforts to reduce the number of head impacts in football practices,” said Jillian Urban, Ph.D., MPH, assistant professor of biomedical engineering at Wake Forest.
According to existing research, there is wide variability in the amount of head injuries players can sustain in a single season. Players between ages 10 and 13 can experience between 26 and 1,003 head impacts, and high school students can have more – between 129 and 1,258. Most do not result in concussions or even any acute signs or symptoms, but the worry remains that repetitive sub-concussive impacts can still cause brain damage in these athletes, the team said.
For this study, Urban’s team followed a group of 47 youth football players between 2012 and 2017. Each player participated in at least two or more consecutive season, and they all wore specially designed helmets, during practices and games, that included the Riddell Head Impact Telemetry System™ that measures linear and rotational head accelerations that occur during a head impact. The captured data was transmitted in real-time via radio waves to a data collection unit on the sidelines.
Imaging data from two football athlete subjects showing a comparison between abnormal voxels from the season with the higher 50th percentile number of impacts per practice session and abnormal voxels from the season with the lower 50th percentile number of impacts per practice session. The season with the lower impact frequency in practice sessions was associated with fewer abnormal voxels compared to the season with a higher impact frequency in practice sessions for both athletes.
All total, the collected data included 109 football athlete-seasons and 41,148 head impacts. The team examined the number of impacts, 50th percentile of impacts per season, 95th percentile peak linear and rotational accelerations, and risk-weighted cumulative exposure that looks at head impact frequency and magnitude over a single season. None of the events resulted in a concussion, the team said.
The investigators captured diffusion tensor imaging (DTI) MRI scans on 19 of the athletes both pre- and post-season for two consecutive football seasons. They compared those results to DTI images taken four months apart of a control group of 16 athletes who participated in non-contact sports, such as swimming, tennis, and track. Urban’s team examined the images for abnormal white matter voxels – those in which DTI scalar values increased or decreased significantly throughout the season.
Based on their data and analysis, the team determined that the number of HIE fluctuated between seasons, as did the abnormal voxel changes. But, they did identify a significant positive correlation between changes in the number of head impacts per practice session and every DTI scalar metric. In addition, they pinpointed significant positive correlations between changes in 50th percentile impacts per practice session and 50th percentile impacts per football session (both practices and games) and DTI scalar metrics.
The DTI trends, they noted, changed for individual players from season to season. This could be due to changes in teams, coaching practices, or positions played.
“These results suggest that, among individual athletes, increases in HIE from one season to the next were associated with a greater number of abnormal voxels and that decreases the HIE were associated with fewer numbers of abnormal voxels from one season to the next,” the team said. “There are a growing number of studies showing significant associations between HIE metrics and both neuroimaging and cognitive function during single-season evaluations of youth through collegiate football players, even in the absence of a clinically diagnosed concussion.”
In light of these findings, the team said, efforts should be made to reduce the number and frequency of head impacts for players, particularly in practice where the majority of them occur. Limiting these events could reduce the number of abnormal imaging findings from season-to-season.
“In an upcoming study, we plan to engage stakeholders in the youth football community to develop and test practical solutions informed by the biomechanical data we collect on field to reduce head impacts in practice,” Urban said.