A MODIFIED FINITE ELEMENT MODEL OF A POROVISCOELASTIC INTERVERTEBRAL DISC

Abstract

The intervertebral disc (IVD) is the soft tissue between the vertebral bodies, which is responsible for transmitting multi-directional loads through the spine and to allow relative motion between the vertebral bodies. The IVD is composed of three distinct tissues, including the nucleus pulposus, annulus fibrosus, and the cartilaginous endplates. Each of these tissues has a characteristic composition and structure which provide them with unique mechanical properties. Among these, nucleus pulposus and annulus fibrosus due to their intricate time-dependent mechanical response has always been the topic of interest for the researchers. Here, we aimed at establishing a patient-specific 3D finite element (FE) model of human IVD based on the poroviscoelastic constitutive law. The main objective was to use the data of tensile stress-relaxation tests on the annulus and nucleus regions to find the poroviscoelastic material constitutive law. The model assumed that the disc is a two-phase body consisting of a water-saturated solid matrix. To do that, the available data in the literature was used as the primary material properties of our model. Thereafter, a set of compressive and tensile loadings was applied on the established patient-specific model of the IVD and the FE results of the poroviscoelastic model were compared to the experimental data. This allowed us to determine a new set of revised parameter values for the poroviscoelastic model which will have practical implications for any future FE studies.