Finite Element Application in Prediction of Suitable Material Properties for an Arthroplastic Lumbar Disc

Diseases of lumbar spine and associated diseases of the intervertebral disc are a major focus of contemporary spinal care. Low back pain, in fact, is becoming in the recent years one of the most diffuse chronic pathologies. Ascribed to the prevalence of low back pain- mostly caused due to disc degeneration, and limitations of current treatments, arthroplasty has been propounded for replacing the degenerated disc. A three-dimensional finite element model (FEM) of the L3-L4 motion segment using ABAQUS v 6.9 has been developed. The annulus fibrosus of the model is idealized as an inhomogeneous composite of an isotropic ground substance, reinforced by helically oriented collagen fibers. The model took into account the material nonlinearities and is imposed different loading conditions. In this study, the model is validated by comparison of its predictions with several sets of experimental data. Disc deformation under compression and segmental rotational motions under moment loads for the normal disc model agreed well with the corresponding in vivo studies. We determined the optimal Young's modulus as well as the Poisson's ratio for the artificial disc under different physiologic loading conditions by linking ABAQUS with MATLAB 2010.a. The results of the present study suggest that a well-designed elastic arthroplastic disc preferably has an annulus modulus of 19.1 MPa and 1.24 MPa for nucleus section and Poisson ratio of 0.41 and 0.47 respectively. Elastic artificial disc with such properties can then achieve the goal of restoring the disc height and mechanical function of intact disc under different loading conditions and so can reduce low back pain.