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Episode 64: Study Demonstrates Causal Link Between Repetitive Head Impacts and CTE

In this week’s episode of Brain Injury Insider, host Michael Kaplen discusses important news about a new study which demonstrates a clear causal link between repetitive head impacts and CTE.

Is the sky falling? 

You bet it is, and it couldn’t happen soon enough to prevent brain damage caused by repetitive head trauma.

This week, I received a group email from a noted defense attorney who defends colleges, universities, professional teams, children’s football leagues and other groups being sued for sports related brain injuries caused by inadequate supervision, failing to remove athletes from play when a concussion or a suspected concussion happens, permitting athletes to return to play before they are symptom free, endorsing and permitting dangerous conduct, and failing to provide athletes, coaches, trainers and other responsible for health and safety with proper education about the risks and dangers of concussions and the long term consequences.

The email said this attorney received numerous inquiries from his clients concerned about a recent study which found conclusive evidence that repeated head trauma leads to chronic traumatic encephalopathy (CTE), an incurable brain disease and how this study would affect current and future sports related brain injury litigation.

The attorney’s answer was, Don’t worry, the sky isn’t falling”.  My response to this attorney was, “You Better Wear a Helmet”

First some background:

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with a history of repetitive head impacts.  CTE was described in boxers as early as the 1920s and by the 1950s it was widely accepted that hits to the head caused boxers to become “punch drunk.”   It has been conclusively established that CTE found in the brains of boxers is caused by repetitive head trauma.

CTE can only be definitively diagnosed following a neuropathological examination.  In reviewing the brains of deceased athletes, neuropathologists have found CTE in the brains of football players, hockey players, soccer players, and most recently rugby players.  The pathological changes in the brains of these players are the same as the damage found in the brains of boxers.  CTE has been found in all ages of players exposed to repetitive head trauma.

CTE is a progressive neurological disease resulting in cognitive, behavioral, and emotional injuries.   The disease is found in brains which have a buildup of abnormal tau protein that can disable neuropathways and lead to a variety of clinical symptoms. These include memory loss, confusion, impaired judgment, aggression, depression, anxiety, impulse control issues and sometimes suicidal behavior.

The study by noted researchers and clinicians from nine universities and the prestigious Concussion Legacy Foundation determined athletes in contact sports are 68 times more likely to develop CTE than the general public. The study is entitled:  “Applying the Bradford Hill Criteria for Causation to Repetitive Head Impacts and Chronic Traumatic Encephalopathy “  The study is published in the journal, Frontiers of Neurology, July 2022 and can be found online at

The study utilized the Bradford Hill criteria, a widely accepted scientific framework to determine if one can justifiably move from an observed association to a verdict of causation and concluded there is a definitive link between repetitive head trauma and CTE.

Sports organizations including the NFL, are members of the Concussion in Sports Group (CISG), a global consortium of sports organizations which has denied a causal link, between repeated head hits and CTE. 

The research paper strongly criticizes the CISG for using what is described as faulty methodology and being funded by the very organizations it is supposed to police.

The denials are similar to those of the tobacco industry who for years denied the link between tobacco and lung cancer.

The researchers are calling on sports and government bodies to implement prevention and mitigation efforts, especially for children, who are “too young to legally consent to any potential long-term risks.”

Chris Nowinski, one of the study authors, co-founder and CEO of the Concussion Legacy Foundation said the study’s findings should be a wake-up call to all youth sports about taking head contact out of the game, whether heading in youth soccer or tackling in youth football

So is the sky falling?   Determining causation between repetitive head trauma and CTE has significant legal consequences for professional and amateur sports leagues and will affect state and federal regulation of sports, and more particularly contact sports.  

Lawsuits by athletes in the in the past claiming CTE was caused by repetitive head trauma against Pop Warner Football, the National Collegiate Athletic Association, and The National Football League, the National Hockey League have met with limited success because of the inability to prove a definite link. 

This study may change judicial attitudes towards proof of causation, and future cases may establish a causal connection between repeated blows to the head and the development of CTE.

The study may also change the attitude of parents in permitting children to engage in sports such as football and ice hockey.

Additionally, this study will cause legislative bodies to look closely at efforts to limit head contact in sports including mandating tag football in place of tackle football for children, limiting the number of concussions a player can sustain before being permanently barred from further participation and imposing more educational requirements on coaches and trainers.

Audio version

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