Effect of a pedicle screw fixation system on lumbar spinal segments: A finite element study

Abstract

Objective: Spinal implants have been used to stimulate fusion by surgical adjustment and correct abnormal alignment of the vertebral column. Spinal fusion can cause some spinal disorders and hence describing the changes in biomechanical forces would help to understand these complications. In this study, we used two lumbar mod-els. One of them is used without the fixed pedicle screw system, and the other one was used with that system. Therefore, we aimed to investigate the biomechanical effect of a pedicle screw fixation system on the lumbar functional spinal unit under applied forces. Material and Meth-ods: Computed tomography data of a scoliotic patient was used for the construction of the lumbar models. The second and third vertebrae (L2-L3) of the lumbar spine, two facet joints, an intervertebral disc, and ligaments were constructed. A screw fixation system was employed and Von-Mises stress analysis was carried out for both models. Results: The von Mises stress distribution results showed that the presence of fixed implantation transmitted the compressive forces to the screws and rods in all directions and decreased the stress levels considerably by al-lowing to stabilize the model. The upper side of the L2 vertebra was the most affected region in flexion and lateral bending. However, the pedi-cle region had the maximum affected area under applied loads in ex-tension and axial rotation. Conclusion: It was concluded that a fixed implant system preserves the maintenance of the vertebral column and decreases the stress on the adjacent spinal segments, especially for the intervertebral discs.