Repetitive Head Injuries, Duration of American Football Play Tied to CTE Severity

The number and force of repetitive head injuries along with time played was associated with CTE severity in men who played American football.

The number and acceleration of repetitive head injuries and career duration are associated with chronic traumatic encephalopathy (CTE) severity in men who play American football. These are the findings of a study published in the journal Nature Communications.

Previous research suggests that a history of repetitive head impacts is associated with an elevated risk for CTE; but the factors of repetitive head injury exposure that underlie this relationship are unclear, according to researchers. Past analyses, from the Understanding Neurologic Injury and Traumatic Encephalopathy and the Framingham Heart Study datasets, have incorporated variables such as estimated number of head impacts, position played, level of play, and career duration. For the current study, the researchers leveraged more recent data from helmet sensors that measured head acceleration, both linear and rotational.

The researchers combined the older and newer datasets for 631 brain donors, through 2020, who had played American tackle football. Adapting a commonly used occupational exposure method, they created “position exposure matrices.” While the matrix for 1 risk model relied on the estimated total number of head impacts, another model also included the newer estimates of cumulative linear and rotational acceleration across players’ careers.

These results provide additional evidence that repeated nonconcussive injuries are associated with CTE pathology.

Logistic regression analyses were performed to determine how well each model predicted CTE diagnosis and severity; linear regression was used to compare model predictions of CTE-associated neurofibrillary tangle burden. Bayesian information criteria analysis was used to compare goodness of fit among the models, relative to the clinical data.

When analyzing models, the researchers found that models that incorporated linear (CTE diagnosis: odds ratio [OR], 1.20; 95% CI, 1.15–1.25; CTE severity: OR, 1.19; 95% CI, 1.12–1.26) or rotational (CTE diagnosis: OR, 1.22; 95% CI, 1.16–1.29; CTE severity: OR, 1.20; 95% CI, 1.13–1.28) acceleration most strongly predicted CTE status. Bayesian information criteria analysis also indicated that these models best fit the donors’ clinical and pathological CTE data.

Lower strengths of association were observed for the models that included only the total number of head impacts, or only cumulative duration of play. Playing position and level of play generally were not associated with diagnosis or severity of CTE, or with neuropathological burden.

On average, athletes died at age 59.7 (standard deviation [SD], 20.1) and played 12.5 years of football (SD, 5.9). A total of 180 athletes did not have CTE; 163 had low-stage CTE (stage I or II); and 288 had high-stage CTE (stage III or IV).

The researchers noted a direct association between mean duration of play and CTE severity. The mean duration of play for those without CTE was 9.5 (SD, 5.3) years; 11.6 (SD, 5.0) years for those with low-stage CTE; and 15.0 (SD, 5.7) years for those with high-stage CTE. Moreover, there was a direct correlation between the number of hits and total g-forces of those hits and CTE. Severity of CTE was associated with a greater number of hits and greater g-forces.

One study limitation was that football players who donate their brains tend to have a higher risk for CTE than the wider population of football players; this may limit generalizability. Also, data on head impacts related instead to military service or other contact sports were not available. Finally, the data do not reflect more recent changes in football play style.

“These results provide additional evidence that repeated nonconcussive injuries are associated with CTE pathology. This is in contrast to the emphasis on concussions that is often discussed in the medical and lay literature,” the researchers wrote. They concluded, “[I]f validated, could be used to identify changes to policy or gameplay that might limit CTE risk by decreasing cumulative exposure, such as by limiting duration of exposure, the number of exposures, and the magnitude of those exposures.”

Disclosures: Several study authors have declared affiliations with biotech, pharmaceutical, and/or device companies, as well as relevant legal commitments. Please see the original reference for a full list of the authors’ disclosures.

References:

Daneshvar DH, Nair ES, Baucom ZH, et al. Leveraging football accelerometer data to quantify associations between repetitive head impacts and chronic traumatic encephalopathy in males. Nat Commun. Published online June 20, 2023. doi:10.1038/s41467-023-39183-0