The human spinal cord : an improved physical model

Spinal cord injury is a devastating condition which can occur by impact of bone fragments during spinal fracture as well as from spinal motion which exceeds the normal physiologic range. The deformation undergone by the spinal cord during these injuries is currently poorly understood. This information is important for the validation of mathematical models of spinal cord injury and in the evaluation of animal models to determine if they are representative of human spinal cord injuries. An accurate surrogate physical model of the human spinal cord would allow measurement of the cord deformations during in vitro spine injury experiments. The objectives of this study were to develop a physical model of the in vivo human spinal cord. This included identifying a material which matches the in vivo modulus of elasticity of the spinal cord, testing its behaviour in uniaxial tension and transverse compression with and without the dura mater and the CSF present. QM Skin 30 elastomer was identified as the best surrogate material for the in vivo human spinal cord. The modulus of elasticity of QM Skin 30 in tension and compression matched that reported for the in vivo spinal cord. A burst fracture injury was simulated with the dura mater and CSF surrounding the surrogate cord indicating that this form of the surrogate cord is the best match for the in vitro bovine spinal cord in similar conditions. Uniaxial tension tests performed at different strain rates indicated that it is viscoelastic. However, the viscoelasticity of the surrogate cord is less than desired. A quasilinear viscoelastic and general linear model were presented to describe the relaxation and creep response. The surrogate cord developed in this study incorporates a range of mechanical properties which have been reported for the spinal cord but which have not all been included in one surrogate cord before now. By virtue of its concordance with in vivo spinal cord properties and our advanced understanding of its behaviour it is appropriate for in vitro spine experiments.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat