Subconcussive head impact exposure and white matter tract changes over a single season of youth football

Purpose: To examine the effects of subconcussive impacts resulting from a single season of youth (age range, 8-13 years) football on changes in specific white matter (WM) tracts as detected with diffusion-tensor imaging in the absence of clinically diagnosed concussions. Materials and Methods: Head impact data were recorded by using the Head Impact Telemetry system and quantified as the combinedprobability risk-weighted cumulative exposure (RWE_cp). Twenty-five male participants were evaluated for seasonal fractional anisotropy (FA) changes in specific WM tracts: The inferior fronto-occipital fasciculus (IFOF), inferior longitudinal fasciculus, and superior longitudinal fasciculus (SLF). Fiber tracts were segmented into a central core and two fiber terminals. The relationship between seasonal FA change in the whole fiber, central core, and the fiber terminals with RWE_cp was also investigated. Linear regression analysis was conducted to determine the association between RWE_cp and change in fiber tract FA during the season. Results: There were statistically significant linear relationships between RWE_cp and decreased FA in the whole (R² = 0.433; P = .003), core (R² = 0.3649; P = .007), and terminals (R² = 0.5666; P , .001) of left IFOF. A trend toward statistical significance (P = .08) in right SLF was observed. A statistically significant correlation between decrease in FA of the right SLF terminal and RWECP was also observed (R² = 0.2893; P = .028). Conclusion: This study found a statistically significant relationship between head impact exposure and change of FA value of whole, core, and terminals of left IFOF and right SLF's terminals where WM and gray matter intersect, in the absence of a clinically diagnosed concussion.