Investigation of the effects of repetitive subconcussive head impacts on white matter in soccer players with multi-shell diffusion tensor imaging

Objective: To determine the long-term microstructural changes in the white matter caused by repetitive subconcussive head impacts in soccer players playing in different field positions (goalkeeper, midfield or defense) in the regional amateur league. Materials and Methods: Seventeen young male soccer players who had played amateur league soccer for at least 10 years were included in the study: 17 for the defender group, 12 for the midfield group, and 13 for the goalkeeper group. Ondokuz Mayıs University Scientific Research Projects Coordination Unit approved the study as a thesis project (PYO.TIP.1904.22.014) and provided the necessary financial budget. In addition to conventional MRI sequences, all participants underwent SWI to evaluate microbleeding foci and Multi-Shell Diffusion Tensor Imaging to evaluate microstructural abnormality. Operator-independent TBSS was used for data analysis. CogniFit™ General Cognitive Assessment (GCA) test was used to assess cognitive functions. Results: Intergroup differences for microstructural changes were most pronounced between the defense group and the midfield group. In the defense group, we found decreased FA and ICVF and increased MD and RD in the right IFOF, right CST and left SLF; increased MD and RD and decreased ICVF in the bilateral ATR, right cingulum, forceps major, bilateral ILF, right SLF, left CST and left IFOF; increased MD in the left cingulum; and increased RD in the bilateral UF compared to the midfield group. Smaller differences were found between defense-goalkeeper and midfield-goalkeeper positions. When the goalkeeper group was compared with the defense group, we found a decrease in left ATR, forceps minor and FA values in the left cingulum in the defense group. When the goalkeeper group was compared with the midfield group, we found a significant decrease in AD values in the right CST, right cingulum, right IFOF and right SLF in the midfield group. No significant difference was found between the groups in neurocognitive tests. Conclusion: This study demonstrated decreases in ICVF values in multiple white matter tracts indicating decreased axonal density, decreases in FA indicating decreased axonal integrity, increases in MD indicating decreased axonal density and myelinization, decreases in AD reflecting axonal damage, and increases in RD indicating impaired myelin sheath integrity. Among all comparisons, defenders had the worst and goalkeepers the best measurements. Differences were most pronounced for ICVF, followed by RD and FA. Differences were less extensive for MD and much more limited for AD. The fact that the increase in RD affected more regions than the decrease in AD suggests that demyelination is an important factor among the pathological changes in defenders, who are thought to be exposed to more head impacts than midfielders. The lack of significant differences in neurocognitive test scores between the groups suggests that imaging measurements can reveal pathologic changes in tissue before the onset of functional symptoms.