Finite element stress analysis of an intervertebral disc.

Abstract An axisymmetric finite element model is employed for the study of the behavior of an intervertebral disc under axial loading. By matching experimental results on the overall behavior of the disc, orthotropic linear material constants are obtained for the annulus fibrosis for various load levels. Results are then presented on the effects of material properties and geometry on the stress-distribution and intradiscal pressures. It is shown that: (1) an adequate representation of disc behavior requires the inclusion of material anisotropy; (2) material properties of the annulus obtained by direct measurement underestimate the stiffness of the material; (3) reasonable predictions of variations of disc stiffness with vertebral level can be made on the basis of geometry; and (4) degenerative changes associated with loss of elasticity have little effect on the intradiscal pressure, while annular tears result in reduced pressure in agreement with clinical observations.