Biomechanical properties of the superior sagittal sinus-bridging vein complex

Finite element models (FEM) of the head are frequently used to simulate traumatic brain injury, leading to a better understanding of brain injury tolerance. The strength of a FEM of the head is dependent on the use of correct material characteristics, experimentally derived for each intracranial tissue, including parasagittal bridging veins (BV). These veins are prone to rupture in their subdural portion upon head impact, giving rise to an acute subdural hematoma (ASDH). The junction of these veins to the superior sagittal sinus (SSS) has been described as an area with distinct vein wall architecture. To understand the biomechanical characteristics of acute subdural hematoma, we studied the SSS-BV complex by loading it to failure in a tensile test. 37 BVs from 9 fresh cadavers were dissected, leaving small strips of SSS attached to the veins. The units were clamped on the SSS and the cortical end of the BV. Strain rates ranged from 0.1-3.8 s(-1). From force-time and strain-time histories, we calculated ultimate strain (epsilon(U)), ultimate stress (sigma(U)), yield strain (epsilon(Y)), yield stress(sigma(Y)) and Young's modulus (E). A mixed-model multivariate analysis of variance (MANOVA) was used to study correlations and strain rate sensitivity of these parameters. We found no strain rate sensitivity. The biomechanical response of the SSS-BV unit in this study was found to be stiffer than reported biomechanical behavior of bridging veins. We conclude that the SSS-BV junction plays an important role in bridging vein rupture, and warrants further investigation to provide FEM with correct material properties for bridging veins.