Assessment of intervertebral disc degeneration-related properties using finite element models based on \(\uprho _H\)-weighted MRI data

Quantitative magnetic resonance imaging (MRI) provides useful information about intervertebral disc (IVD) biomechanical properties, especially those in relation to the fluid phase. These properties may improve IVD finite element (FE) models using data closer to physiological reality. The aim of this study is to investigate IVD degeneration-related properties using a coupling between MRI and FE modeling. To this end, proton density (\(\rho _H\))-weighted MRI sequences of a porcine lumbar IVD were carried out to develop two biphasic swelling models with hyperelastic extracellular matrix behavior. The first model is isotropic, and the second one is anisotropic and takes into account the role of collagen fibers in the mechanical behavior of the IVD. MRI sequences permitted to determine the geometry and the real porosity mapping within the disc. The differentiation between disc components (nucleus pulposus, annulus fibrosus and cartilaginous end plates) was taken into account using spatial continuous distributions of the mechanical properties. The validation of the FE models was performed through two steps: the identification of the model’s mechanical properties using relaxation compressive test and the comparison between the MRI after load porosity distributions and those numerically obtained using the set of identified properties. The results confirmed that the two developed FE models were able to predict the mechanical response of uniaxial time-dependent compressive test and the redistribution of porosity after load. A slight difference between the measured and the numerical local bulges of the disc was found. This study suggests that from the coupling between MRI imaging in different state of load and finite element modeling we can deduce relevant information that can be used in the assessment of the early intervertebral disc degeneration changes.