Design and Mechanics of TLIF/ELIF Implants

Lumbar interbody fusion is the standard treatment for degenerative disc disease. This study served to compute the stress levels and load transfer in a composite structure, consisting of fusion implant, bone-graft that finally becomes fusion-bone, and rods of the dorsal stabilisation. The implant was represented by different materials and the fusion process was simulated by increasing Young's moduli of the bone-graft / fusion-bone component. Fusion implants with a low Young's modulus produce a higher stress and load in the bone-graft / fusion-bone which is advantageous for the fusion, but subject the rods of the dorsal stabilisation to bending stress additionally to axial stress which bears the risk of pedicle screw failure.