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Identification of viscoelastic property of intervertebral disc under flexion, extension and lateral bending.

Viscoelastic behavior of the functional spinal unit (FSU) under the application of moment is important for the biomechanical understanding of physiological and pathological aspects of spine. This paper presents a mechanical model on viscoelastic behavior of intervertebral disc connecting two vertebral bodies where a posterior element and surrounding tissues have been removed from FSU. The model, which is composed of a nonlinear spring and a linear Kelvin element in series, is proposed. Specimen of human lumbar intervertebral disc (L3-intervertebral disc-L4) are used for the experiment of the cyclic moment application of flexion, extension and lateral bending with constant loading rates. Simulations by the proposed model are compared with the experiment. It is suggested that the model is good for the prediction of viscoelastic behavior of the intervertebral disc.