Numerical study of intervertebral prosthesis

Lumbar interbody fusion is a lumbar surgical procedure that consists of replacing the intervertebral disk with a stiff prosthetic device (the fusion cage), with the purpose of promoting bone growth in between the two vertebrae and finally fuse them into one single rigid unit. The numerical studies described in this paper are oriented to clarify the mechanical behavior of the new vertebral configuration after the fusion cage has been installed. The geometrical model includes vertebrae L5 and S1 and has been directly generated from radiological images, with individual representation of the stiffer cortical bone on the surface and the softer trabecular bone in the interior, as well as two kinds of prosthesis devices in between the two vertebrae. The resulting stresses are discussed on the basis of a hyperbolic Mohr-Coulomb failure criterion in comparison to traditional von Mises