Sports-related concussions have received considerable attention for both their immediate and long-term consequences, leading to rules changes and comprehensive concussion protocols to increase athlete safety. When a concussion is suspected, the current standard of care is to remove the athlete from play and use a variety of neurocognitive assessment tools to try and diagnose the severity of observable or self-reported symptoms. However, a significant body of research has revealed that physiological changes in the brain resulting from the accumulation of many small direct or indirect head impacts, none of which on their own trigger any concussion symptoms, can also lead to neurological injuries and long-term degenerative neural disorders such as CTE. Physiological and behavioral impairments that can be caused by such “sub-concussive” head impacts have now been thoroughly documented using structural and functional brain imaging, neurophysiological testing, cognitive and behavioral testing, on-field monitoring and computer simulations of head impact biomechanics, neural cell cultures and atomic force microscopy, animal studies, and human brain autopsies. The results all highlight an urgent need for more effective tools to monitor young athletes and their collegiate and professional counterparts, so that sub-concussive injury risks can be tracked and minimized over time.
HEAD IMPACT INJURIES IN CONTACT SPORTS TODAY
In a recent collaboration funded in part by an NFL / GE Healthcare Head Health Challenge grant, researchers from Protxx and the University of California Santa Barbara (UCSB) Brain Imaging Center combined powerful new high-angular-resolution diffusion spectrum MRI (DSI) brain imaging techniques and novel wearable head impact monitoring techniques to observe the onset, spatial distribution, and temporal evolution of both transient and persistent changes in neural tissues resulting from cumulative sub-concussive head impact exposure in NCAA athletics. Although the vast majority of routine head impacts were found to be well below thresholds above which single impacts have a high probability of triggering concussion symptoms, routine cumulative daily impact loads were often well above these thresholds.
A threshold cumulative daily head impact exposure dose was also observed, above which DSI imaging revealed the onset and accumulation of wide-spread changes in neural tissues throughout the season. A similar threshold behavior has also been observed in recent studies that directly measured the forces required to morphologically deform axons, mechanically break microtubules in axons, impair axonal transport, trigger focal axonal swelling, and eventually compromise axonal survival. The corresponding threshold forces fall well within the range predicted by finite element models to be generated by routine sub-concussive head impacts in many athletic activities.
Correlating Impact Exposure With Clinical and Performance Data
The above threshold behavior as a function of cumulative head impact power underlies the Protxx head impact dosimeter, a small wearable device that can provide objective remove-from-play guidance before cumulative head impact exposures exceed potential neural damage thresholds. The Protxx dosimeter functions as a very sensitive "seismometer for the brain", registering impacts that can lead to deformation of neural tissues, and warning when cumulative exposures approach damage thresholds.