Soccer players who headed a ball above a threshold of 1,800 headings per year demonstrated poorer memory scores and those above thresholds of 885 to 1,550 hits, depending on location, suffered white matter abnormalities, researchers reported in a study published online June 11 in Radiology.
Sports-related head injury has been linked with multiple adverse consequences. However, despite the prevalence of heading in soccer, few studies have examined the clinical significance of subconcussive heading as a cause of brain injury. Players head the ball, on average, six to 12 times during competitive games, where balls can travel at velocities of 50 miles per hour or more. During practice sessions, heading drills, where the ball is headed repeatedly up to 30 or more times, are commonplace.
Michael L. Lipton, MD, PhD, medical director of MRI at Montefiore Medical Center in New York City, and colleagues devised a study to investigate the association between soccer heading and subclinical evidence of traumatic brain injury (TBI).
The researchers enrolled 37 amateur soccer players, 28 men and nine women, average age 30.9 years. Participants completed a questionnaire to estimate heading in the previous 12 months and lifetime concussions. They underwent a cognitive function test to assess psychomotor speed, attention, executive function and memory; and whole-brain MRI was performed to identify a link between heading and fractional anisotrophy (FA).
Results indicated a relationship between heading and FA at three locations in temporo-occipital white matter at thresholds of 885 to 1,550 headings per year. “Lower levels of FA were also associated with poorer memory scores, with a threshold of 1,800 headings per year.”
Lipton and colleagues suggested that intrinsic repair mechanisms mend low-level injury, as is the case in most patients with mild TBI. However, these mechanisms may be unable to compensate for cumulative injury beyond certain thresholds. “Virtually all subjects with exposures exceeding the threshold levels had low FA, suggesting that heading above some defined level may be generally unsafe.”
In addition, a subset of individuals with exposure below the threshold had FA and cognitive performance below the group mean, suggesting some individuals may be at higher risk after modest exposure, according to Lipton and colleagues.
Concussion history was not associated with FA or cognitive performance.
The researchers suggested several strategies to address these effects, including prospective monitoring of exposure to identify a cut-off point for curtailing heading, further study to identify risk factors for subclinical injury and additional research to develop evidence-based protective strategies for safe soccer play.