Finite element analysis of the biomechanical changes following unilateral laminotomy for bilateral decompression in lumbar spine

English Keywords:Unilateral laminotomy and bilateral decompression  Biomechanics  Finite element analysis  Lumbar

English Abstract:

  【Abstract】 Objectives: To evaluate the biomechanical state of the L4-L5 segment after unilateral laminotomy for bilateral decompression(ULBD) surgery using finite element analysis, providing a theoretical basis for the treatment of lumbar degenerative diseases with ULBD. Methods: Thin-slice CT scan data from the lumbar spine of a healthy volunteer were extracted, and high-fidelity three-dimensional finite element methods were applied to establish normal L4-L5 model, post-ULBD surgery model, and post-lumbar fenestration(LF) surgery model. The L5 vertebral body′s lower endplate was fully fixed in all the models, and a 500N axial load was applied at the L4 upper endplate, along with a 10N·m bending moment load in six directions of flexion, extension, left lateral bending, right lateral bending, left rotation, and right rotation. Comparative analysis of the biomechanical characteristics such as intervertebral disc compression height, intervertebral range of motion(ROM), stress distribution within the intervertebral disc, and facet joint pressure was conducted under different loads for the three models. Results: The ROMs under six directions of movements were within the range of the measured results of previous cadaveric studies, verifying that the normal model was valid. Under the 500N axial load, the intervertebral disc compression heights for the normal model, post-ULBD and post-LF surgery models were 0.74mm, 0.85mm, and 0.85mm, respectively. With an additional 10N·m bending moment load, the intervertebral ROM in flexion, extension, left lateral bending, right lateral bending, left rotation, and right rotation for the normal model were 6.1°, 4.2°, 5.1°, 4.6°, 2.9°, and 2.6°, respectively; for the post-ULBD model, they were 6.5°, 4.8°, 6.0°, 5.2°, 3.2°, and 2.9°, respectively; and for the post-LF model, they were 6.4°, 4.6°, 5.6°, 5.1°, 3.0°, and 2.8°, respectively. There was no significant difference in the stress distribution within the intervertebral disc for the three models, with the maximum von Mises stress occurring at the outer annulus fibrosus on the compressed side of the disc. The maximum von Mises stress in the intervertebral disc for the normal model under flexion, extension, left lateral bending, right lateral bending, left rotation, and right rotation was 0.52MPa, 0.66MPa, 0.81MPa, 0.87MPa, 0.46MPa, and 0.40MPa, respectively; for the post-ULBD model, it was 0.64MPa, 0.76MPa, 1.06MPa, 1.13MPa, 0.60MPa, and 0.64MPa, respectively; and for the post-LF model, it was 0.65MPa, 0.80MPa, 1.00MPa, 1.06MPa, 0.66MPa, and 0.65MPa, respectively. Significant facet joint contact pressure was observed under left and right rotation, with the normal model showing contact pressure of 60N and 69N, the post-ULBD model showing 30N and 87N, and the post-LF model showing 79N and 120N. Conclusions: After ULBD surgery, there is an increase in lumbar intervertebral disc compression height, intervertebral ROM, stress within the intervertebral disc, and facet joint pressure. Compared with LF surgery, ULBD has a smaller impact on the biomechanical stability of the lumbar segment.