Force of hit won't predict concussion severity

NEW YORK (Reuters Health) - The severity of concussions sustained by football players can't be predicted by how hard they are hit, or where the hit occurs, new research shows.

The findings suggest "there are likely other contributing factors that influence the occurrence of a concussion as well as the rate of recovery after the concussion," such as a player's having had a concussion in the past or several recent, smaller blows to the head, Dr. Kevin M. Guskiewicz of The University of North Carolina in Chapel Hill and colleagues say.

Sport-related concussions, sustained by 300,000 US children, teens and young adults every year, are now seen as a "major public health concern," Guskiewicz and his team note. "Deciding when an athlete can safely return to participation after a concussion is perhaps the most challenging task of any sports medicine clinician," the researchers add in the journal Neurosurgery.

To better understand how severity of head impact relates to the likelihood of concussion, Guskiewicz and his team conducted three studies of Division I football players who had acceleration-measuring embedded in their helmets.

Some sports medicine investigators have suggested that an impact must be 70 to 75 times the force of gravity (g) or greater for a concussion to occur.

In the first study, the researchers looked at 88 players over three seasons, during which time 13 concussions occurred at impacts ranging from 60.51 to 168.71 g. They found no relationship between the force of an impact or where an athlete's head was hit and the severity of his symptoms. They also found no association between the size or location of the hit and players' brain function and postural stability after the injury.

In the second study, Guskiewicz and his colleagues looked at balance and neurocognitive performance in players after impacts above 90 g during practices and games. Twenty-two athletes who sustained impacts of 90 g or above showed no decline in their cognitive performance or balance, the researchers found.

In the third study, the researchers had 76 players wear accelerometer-equipped helmets for two seasons. On average, players sustained impacts of 21 g to 23 g. Less than 0.35 percent of the injuries that exceeded proposed thresholds for concussion actually resulted in concussion, they found.

The bottom line, Guskiewicz said, is that concussions are multifactorial.

"Football players receive concussions by impacts to the head that occur at a wide range of magnitudes, and clinical measures all appear to be largely independent of impact magnitude and location," Guskiewicz noted in a statement.

"People see massive hits and think, 'that's the one!' and ignore more trivial blows," the researcher added. "Now we know that these trivial hits may be just as serious as the harder ones."

SOURCE: Neurosurgery, December 2007.