Finite Element Analysis of Spinal Cord Injury in the Rat

Abstract

A three-dimensional (3D) finite element model (FEM) that simulates the Impactor weight-drop experimental model of traumatic spinal cord injury (SCI) was developed. The model consists of the rat spinal cord, with distinct element sets for the gray and white matter, the cerebrospinal fluid (CSF), the dura mater, a rigid rat spinal column, and a rigid impactor. Loading conditions were taken from the average impact velocities determined from previous parallel weight-drop experiments employing a 2.5-mm-diameter, 10-g rod dropped from either 12.5 or 25 mm. The mechanical properties were calibrated by comparing the predicted displacement of the spinal cord at the impact site to that measured experimentally. Parametric studies were performed to determine the sensitivity of the model to the relevant material properties, loading conditions, and essential boundary conditions, and it was determined that the shear modulus had the greatest influence on spinal cord displacement. Additional simulations were performed where gray and white matter were prescribed different material properties. These simulations generated similar drop trajectories to the homogeneous model, but the stress and strain distributions better matched patterns of acute albumin extravasation across the blood-spinal cord barrier following weight-drop SCI, as judged by a logit analysis. A final simulation was performed where the impact site was shifted laterally by 0.35 mm. The off-center impact had little effect on the rod trajectory, but caused marked shifts in the location of stress and strain contours. Different combinations of parameter values could reproduce the impactor trajectory, which suggests that another experimental measure of the tissue response is required for validation. The FEM can be a valuable tool for understanding the injury biomechanics associated with experimental SCI to identify areas for improvement in animal models and future research to identify thresholds for injury.

Critical values of mechanical stress and strain during traumatic cervical spinal cord injury: Clinical study with the use of Finite Element Modelling

“…Moreover, in the experiment with FEM application they proved that the mechanical load induced by the injury correlates equally strongly with the size of the blood-spinal cord barrier damage. [5] This constituted a principle for undertaking an attempt of FEM application in the analysis of clinical tSCI…”

“…Based on the results reported by Maikos et al [5] it may be concluded that the knowledge about the values and distributions of stress and deformation, which are noted at the moment of SCI, may enable determination of the range of primary and secondary injury. [6,7] This would possibly allow the precise and reliable predicting of actual extent of tSCI and remote neurological after-effects of the secondary injury.…”

“…[16][17][18] Numerous studies on the distribution of spinal cord deformations at the moment of injury were conducted in the past. [3,5,[19][20][21][22] According to our knowledge there was no clinical study describing critical values of mechanical stress and strain for the cervical spinal cord performed previously.…”

Cervical ossification of the posterior longitudinal ligament: factors affecting the effect of posterior decompression

“…23 Although intraspinal stress caused by behavior or compression of the spinal cord was examined by Czyz et al, who developed 3-dimensional spinal cord models, and Maikos et al and Greaves et al, who developed models of the vertebral body and spinal cord, they did not mention the clinical effects of decompression, postoperative assessment, etc. [24][25][26][27] In another study, we had developed a compression model and a posterior decompression model of C-OPLL and performed analysis to demonstrate that intraspinal stress increases with the progression of kyphosis. However, in this study, only the kyphotic angle was made worse.…”

An Experimental and Numerical Investigation of the Mechanical Properties of Spinal Cords

“…The dural sac, with much higher values of Young's modulus and Poisson's ratios lower, when compared to the both kinds of matter, protects them from the high stress and, by doing so, also protects from the spinal cords rupture. In order to analyze the influence of the cerebrospinal fluid, when modeling the mechanisms of the spinal cord's injury, the next model includes such structures, as: the dura mater, the CSF, as well as, the white and gray matters, similar to what has been done by Maikos [53]. The CSF has been modeled using bulk modulus 6.67 kPa, Poisson's ratio 0.49 [53].…”