Nonlinear Viscoelastic Behavior of Human Cervical Spine Ligaments

Introduction—Spinal ligaments play an important role in spine biomechanics. Accordingly, a precise understanding of ligament mechanical properties is requisite for accurate modeling of the local and global behavior of the spine. Spinal ligaments exhibit nonlinear stressstrain relationships and viscoelastic material behavior. Current literature on the viscoelastic response of cervical spine ligaments has focused on forces and displacements experienced during trauma and often utilize the quasi-linear viscoelastic (QLV) theory proposed by Fung to describe this behavior. While researchers have shown success using QLV theory to model relaxation behavior of spinal ligaments at a single magnitude of applied strain, this theory does not allow the relaxation function to vary according to the applied strain. Throughout normal spine movements, ligaments undergo varying levels of applied strain. The lack of information about the viscoelastic behavior of spinal ligaments under multiple magnitudes of applied strain prevents the development of mathematical models to accurately approximate spine behavior. This work investigates the viscoelastic behavior of cervical spine ligaments under varying levels of applied strain.