Design and analysis of infill density effects on interbody fusion cage construct based on finite element analysis

Degenerative Disc Disease is a condition of the spine when the intervertebral disc begins to collapse. This disease occurs in the human spine, especially in the lumbar spine, because the primary function of the lumbar spine is to support the weight of the body. There are many treatments for this disease, and one of the treatment methods is Posterior Lumbar Interbody Fusion (PLIF) surgery. There are few implications of the PLIF surgery, such as cage subsidence, cage failure, cage migration, and highly concentrated stress effect on the cage. The aim of the study was to develop an interbody cage that can be implanted into the spine and reduce the post-operative effects using the Finite Element Analysis (FEA) approach. In this study, various infill densities of the interbody cage were designed using Solidworks software and analyzed using Ansys software. Polylactic Acid (PLA) was assigned as a cage material. The cage was implanted between L4 and L5 to create the three dimensional (3D) model, in which the spine model was developed from extracted CT scan images using 3D Slicer software. The model was analyzed based on von Mises stress and maximum principal stress compared with the yield strength and ultimate tensile strength of the material, respectively. The 3D model was loaded with flexion, extension, axial rotation, lateral bending and compression to mimic the physiological motions of the spine. The analysis showed that the interbody cage with 50% infill density has been identified as the most appropriate design according to the acceptable range of stresses generated, fastest estimated printing time, and required the least amount of printing material.