Lifetime exposure to cumulative force of repeated head impacts is strongly associated with CTE
By Maya Chawla. This article was initially published in the 7/14/23 edition of our Concussion Update newsletter; please consider subscribing.
While brain injury prevention in sports has largely focused on concussion, a groundbreaking study published in Nature Communications revealed that the development and severity of CTE are associated with the duration of play and the cumulative force of all repetitive head impacts (RHIs). The charts from the study were reproduced in a New York Times article, in which authors Ken Belson and Benjamin Mueller note that "Those players who absorbed the most cumulative force from head hits had the worst forms of C.T.E.." For one element of the study, authors Daniel H. Daneshvar et al. looked at the concussion history of the brain donors in the study; they found no association between CTE status and the number of concussions they self-reported. There was no association between the number of self-reported concussions and CTE severity for those who had CTE.
Daneshvar and colleagues designed the first "position exposure matrix" (PEM) for American football using data from 34 accelerometer studies. They applied the PEM to the brains of 631 deceased football players diagnosed with CTE who had donated their brains to the Boston University Unite Brain Bank. The PEM retrospectively quantifies the cumulative RHI exposure of football players by position via approximating the total linear and rotational acceleration from impact forces in addition to the total number of RHIs. In addition to their PEM analysis, the study authors looked at stand-alone metrics in relationship to CTE pathology, including position played, duration of playing career, and number of concussions. The only factors with a statistically significant association with CTE pathogenesis were duration of play and PEM-derived measures of cumulative head impact intensity.
A more refined understanding of the aspects of RHI force involved in CTE can guide us in improving care and protection of our athletes. Possible manifestations of this include treating subconcussive hits with more caution in sideline assessments or, as described in the New York Times article, reducing or eliminating contact from practice. Keeping track of head impact history, especially information related to impact forces, may be useful in monitoring athletes' risk, and a PEM such as the one used in this study may be used to do so. Beyond athletics, this study's implications can potentially protect many more populations who experience RHIs, including individuals experiencing intimate partner violence and military personnel exposed to repeated blasts.
This study is evidence that repetitive subconcussive head impacts are implicated in CTE development and should be given more gravity. Repetitive occurrence of force imparted to the brain tissue increases the risk for CTE, regardless of whether the magnitude of each is enough to cause a concussion. Future research should continue expanding the demographics beyond male football players at high levels of competition. Still, this study reflects great progress in our ability to characterize CTE and predict risk, giving us valuable insights to protect the safety of athletes' careers and lives.
