Finite Element Analysis Of Biomechanical Characteristics Of Transforaminal Lumbar Interbody Fusion

Lumbar fusion surgery is an effective treatment for lumbar spine lesions as lumbar spondylolisthesis, which transforaminal lumbar interbody fusion(TLIF)due to less trauma, less blood loss and faster recovery after surgery, is increasingly favored by spine surgeons. Since TLIF should remove one side of zygopophysis joints, the problems about clinical application value of the stability of the lumbar fusion, fusion rate and the impact of the biomechanical properties of the implanted instrument have become the research highlights.The three dimensional model of L4 to L5 lumbar motion segment and the surgical model of TLIF are established based on the CT images and combined with image processing software, which include cortical bone, cancellous bone, rear bony unit, fiber annulus matrix, collagen fibers, nucleus pulposus, cartilage endplate, seven kinds of ligaments and lumbar facet joints and other lumbar structure. Use the finite element method and make a comparative analysis between lumbar range of motion and the biomechanical characteristics of the stress and strain distribution of intervertebral cage and pedicle screw under status of flexion, extension, lateral bending and axial rotation. The main research contents and results are as below:1)Based on the Grid envelope, mesh lumbar model and realize all the grid nodes of the various parts combined together, build the three dimensional nonlinear finite element model of the human lumbar L4~5 segments. The results of normal lumbar model are similar to the research results of previous vitro experiments and the finite element analysis under the same conditions, and verify the validity of the established model.2)Research on the combination of implant method between pedicle screw system(unilateral or bilateral)and interbody fusion cage(1 or 2). The motion range of the model under different operations is reduced above 84% compared with normal model, and the stability is improved significantly. Bilateral pedicle screw fixed or two cages implanted can really share the stress of unilateral pedicle screw and single cage, but there are no statistically significant differences. From the stability of the postoperative and the stress distribution of implants, combined with the clinical, single cage oblique implanted with unilateral pedicle screw fixed can meet the clinical surgical results.3)Research on single cage implanted into intervertebral disc in different locations, when unilateral pedicle screw system fixed(left operating side). The motion range of the model under different operations is reduced above 82% compared with normal model, and the stability is improved significantly. The equivalent stress value of cage and pedicle screw is higher when the distance between them is longer. The stability of lumbar fusion and the stress of internal fixation show both of cage and pedicle screw achieve relatively good surgical results when cage is operating side implanted into intervertebral disc.This paper devotes to the research of implant approach and location of implanted instruments to treat lumbar spondylolisthesis by TLIF, analyze and evaluate the stability and the rate of lumbar fusion and the biomechanical properties of implanted instruments, so as to provide a theoretical basis to choose the right operation plan for clinic and optimize the design of implanted instruments.