A new analysis by Australian and international experts has found there is now conclusive evidence to support a causative link between repetitive head impacts (RHI) and chronic traumatic encephalopathy (CTE).
While sports bodies have long played down a cause and effect relationship between sports concussion and CTE, the new analysis using trusted ‘Bradford Hill criteria’ found robust evidence of a causal relationship, sufficient to confirm the hypothesis, its authors say.
The researchers from the University of Sydney and University of Melbourne, as well as academics from Harvard and Oxford say their findings show there is a need for urgent action from sports organisations, government officials and parents on sports concussion.
“We have the highest confidence in the conclusion that RHI causes CTE. We encourage the medical, scientific and public health communities to now act under the premise of a causal relationship and take immediate action to prevent CTE, minimise risk, and develop therapeutics to slow or stop disease progression,” they write.
In their paper, published in Frontiers of Neurology, they say that until now, policies on RHI and CTE have been guided by consensus statements from the controversial Concussion in Sport Group (CISG), chaired by Dr Paul McCrory. This group, which has questioned or dismissed the quality of evidence around repetitive head injury and long-term neurodegeneration, has been accused of bias through conflicts of interest and funding from corporate sporting groups.
“Developing consensus on CTE causation has important public health and medico-legal implications,” the authors said.
“If RHI causes CTE, then it becomes an environmentally caused brain disease that is preventable. If CTE is environmentally caused, then settings with exposure to RHI, which could include participation in some sports, may become regulated by governmental organisations that oversee workplace and public safety, and individuals and organisations could become financially liable for the care of those who develop CTE.”
In their analysis, the researchers examined the literature on RHI and CTE through the Bradford Hill criteria, which were developed to determine if one can justifiably move from an observed association to a verdict of causation.
The nine criteria include viewpoints such as strength of association, consistency, specificity, temporality, biological gradient, plausibility, coherence, experiment, and analogy.
While acknowledging the criteria could not be used as “indisputable evidence”, the review concluded that the incredible strength of association found, combined with robust evidence in all nine benchmarks “suggests an extremely high likelihood of a causal relationship”.