2024, Vol. 28 ›› Issue (24): 3789-3795

Finite element analysis of interspinous fixation-assisted endoscopic interbody fusion in treatment of severe lumbar spinal stenosis

Liu Jiang1, 2, 3, Zhang Hanshuo3, Ding Yiwei4, Jiang Qiang3, Li Tusheng3, Huang Jie3, Yang Guangnan3, Ding Yu1, 2, 3   

Abstract: BACKGROUND: In clinical application, simple interspinous fixation without additional interbody fusion has similar fixation effects to pedicle screw and rod fusion internal fixation, and can effectively reduce the range of motion of the responsible segment and the stress of the articular process. However, after simple placement of the new interspinous fusion fixation device BacFuse, the stress at the root of the spinous process is relatively concentrated, and the spinous fracture is prone to occur. If an intervertebral fusion cage is inserted in conjunction with interspinous fixation, Von Mises stress can theoretically be dispersed to reduce the risk of spinous fracture. However, there are few studies on biomechanics and finite element analysis.
OBJECTIVE: To observe the biomechanical stability of interspinous fixation-assisted endoscopic interbody fusion in the treatment of severe lumbar spinal stenosis.
METHODS: The normal finite element model M0 of the L4-L5 segment of the lumbar spine was established by Mimics, Geomagic, Solidworks, and ANSYS software based on the lumbar CT images of a 26-year-old adult male volunteer excluding spinal diseases. On the basis of M0, the immediate model M1 after endoscopic decompression combined with interbody fusion, the interspinous fixation device (BacFuse) model M2 after endoscopic decompression, and the interspinous fixation (BacFuse) model M3 after endoscopic-assisted interbody fusion were established. The same stress was applied to the upper surface of the L4 vertebral body in the four groups, and the lower surface of the L5 vertebral body was fixed and supported. The range of motion and the extreme Von Mises stress of the endplate bone and the posterior ligament complex of the vertebral body were analyzed under six working conditions of flexion, extension, left/right bending, and left/right rotation.   
RESULTS AND CONCLUSION: (1) Compared with model M0, the range of motion value of model M1 increased significantly under six working conditions. Model M2 and model M3 had a significant reduction in range of motion. (2) Compared with model M0, the maximum stress of the vertebral body in model M1 did not change significantly under the six working conditions. The maximum stress at the rear of the M2 vertebral body increased significantly. (3) Compared with model M1, the maximum stress of model M3 did not change significantly under the six working conditions. Compared with model M2, the maximum stress of model M3 decreased significantly. (4) Compared with the model M0, the extreme Von Mises stress of the L4 and L5 endplates of the model M1 was significantly increased. The extreme Von Mises stress in L4 and L5 endplates of models M2 and M3 decreased slightly. Compared with model M1, the Von Mises stress of the bone under the L4 and L5 endplate of models M2 and M3 was significantly reduced. (5) It is concluded that the implantation of BacFuse can effectively reduce the bone stress under the endplate during simple interbody fusion, decrease the risk of cage subsidence, diminish the risk of facet joint fracture on the decompression side, and provide a good stable environment for interbody fusion. The placement of an intervertebral fusion cage can reduce the stress of the root of the spinous process, which is beneficial to decrease the risk of fracture of the root of the spinous process.

Key words: severe lumbar spinal stenosis, spinal endoscopy, interspinous fixation, interbody fusion, biomechanics, finite element analysis