Mechanisms and variances of rotation-induced brain injury: a parametric investigation between head kinematics and brain strain.

There lacks a comprehensive understanding of the correlation between head kinematics and brain strain especially deep-brain strain, partially resulting the deficiency of understanding brain injury mechanisms and the difficulty of choosing appropriate brain injury metrics. Hence, we simulated 76 impacts that were focused on concussion-relevant rotational kinematics and evaluated cumulative strain damage measure (CSDM) and average strain that could represent brain strain distribution. For the whole brain, axial rotation induced the highest CSDM, while lateral bending produced the lowest CSDM. However, for the deep-brain components, lateral bending produced the highest CSDM to the corpus callosum and thalamus. We further confirmed that brain strain was mainly produced by rotational kinematics, for which the effect of rotational deceleration could not be ignored with the deceleration influencing CSDM20 up to 27%. Our data supported that peak rotational velocity correlated to brain strain with an average R2 of 0.77 across various impact directions and different shapes of loading curves. The correlation between peak rotational velocity and brain strain reached to an average R2 of 0.99 for each specific impact direction. Our results supported using direction-specific peak rotation velocity for predicting strain-related brain injury. Additionally, we highlighted the importance of investigating whole-brain and deep-brain strain, as well as considering rotational deceleration.