The role of CSF and SAS trabeculae in head/brain injuries: A new local/global and solid/fluid modeling

Blunt and rotational head impacts due to vehicular collisions, falls and contact sports cause relative motion between the brain and skull. This increases the normal and shear stresses in the interface region consisting of cerebrospinal fluid (CSF) and subarachnoid space (SAS) trabeculae. The relative motion between the brain and skull can explain many types of traumatic brain injuries (TBI) including acute subdural hematomas (ASDH). ASDH is caused by the rupture of bridging veins that transverse from the deep brain tissue to the superficial meningeal coverings.; The complicated geometry of the SAS trabeculae makes it impossible to model all the details of the region. Investigators have simplified this layer with solid elements, which may lead to inaccurate results. The goal of this research was to investigate the role of the CSF and SAS trabeculae in the failure of the cerebral blood vessels, ASDH, during blunt and rotational head impacts. Two global models, namely global solid model (GSM) and global fluid model (GFM), were constructed. The relative displacement between the brain and skull was determined from GSM. To determine the CSF pressure and considering the fluid-solid interaction, CSF was replaced by an equivalent fluid. The viscosity of the equivalent fluid was found to mimic the head/brain system. That is, through a damping analysis on an experimental study performed on human cadavers, the damping ratio of the system was evaluated. The damping ratio was used to calculate the equivalent viscosity of the system. The two global models were subjected to two types of load known to create injuries, a blunt impact and a rotational impact. To study the mechanism of the injury, the relative displacement between the brain and skull along with the equivalent fluid pressure were implemented into a new local solid model (LSM). The strains of the cerebral blood vessels were determined from LSM. These values were compared with their relevant experimental ultimate strain values. The results showed an agreement with the experimental values indicating that the applied loads are strong enough to create ASDH.; It has been shown that this research provides a reliable tool to relate the head impacts to ASDH. This contributes to the knowledge of the head/brain biomechanics underlying the understanding of ASDH.