Researchers have found that intentional and unintentional head impacts in soccer are independently associated with moderate to very severe central nervous system (CNS) symptoms.
Michael L. Lipton, MD, PhD, from the Albert Einstein College of Medicine in Bronx, New York, and colleagues recruited 222 amateur soccer players from a substudy of the Einstein Soccer Study to complete a total of 470 online HeadCount questionnaires at baseline and every 2 weeks for the study duration. The recall questionnaires asked about soccer practice and games, heading (a soccer technique that uses the head to control the ball) and unintentional (ball to head, head to head, head to goalpost) head trauma, and the frequency and severity (from mild to very severe) of CNS symptoms.
The mean number of headings every 2 weeks was 44 for men (median 18) and 27 for women (median 9.5); 37% of men and 43% of women reported one or more unintentional head impacts. Symptoms related to heading the ball were reported in 20% (93 out of 470) of the questionnaires.
After controlling for unintentional head impacts, the researchers found that intentional heading in the highest quartile was significantly associated with CNS symptoms (odds ratio [OR] 3.17; 95% CI, 1.57-6.37).
After controlling for intentional heading, participants with 2 or more unintentional head impacts were also at increased risk for CNS symptoms (OR 6.09; 95% CI, 3.33-11.17), as were those with 1 unintentional head impact (OR 2.98; 95% CI, 1.69-5.26).
“These findings suggest that soccer players experience repeated concussive and not simply subconcussive impacts,” the investigators wrote.
The researchers added that the risk of moderate to severe CNS symptoms was substantially higher (OR of 8.36) for the 17.6% of 2-week episodes that had 2 or more unintentional head impacts vs the 20.2% of the 2-week episodes with a single head impact (OR of 3.6).
“More specifically, if a soccer player [had] one unintentional head impact, there was a 47% probability (17.6%/[17.6% + 20.2%]) of having another such event in the same 2-week interval,” the researchers wrote. “It may thus be sensible to intervene with timely coaching when such events occur as a step to reduce the risk of a subsequent event.”
The researchers concluded that in the future, it will be important to examine whether more subtle, transient CNS changes, determined by variations in performance on neuropsychological tests, occur in the absence of severe CNS symptoms. They also noted that because there is evidence of short-term impact on the CNS caused by head exposure in soccer, future research on long-term effects is warranted.
- The researchers examined a relatively young population of adult soccer players in the northeastern United States and therefore cannot generalize their findings to other populations, such as young children or adolescents who may experience different patterns of exposure and may only play soccer during one season per year.
- The researchers cannot generalize their findings to college or professional players.
- It is possible that neck measures are meaningful in more vulnerable players, such as younger or less-experienced players.
- Recall bias or reverse causation is possible, but the researchers conducted their study questionnaires to minimize this and noted that their results match with previous findings.
Stewart WF, Kim N, Ifrah CS, et al. Symptoms from repeated intentional and unintentional head impact in soccer players [published online February 1, 2017]. Neurology. doi:10.1212/WNL.0000000000003657