Stress changes of intervertebral disc after fusion of L4/5 facet joints: a finite element analysis

English Keywords:Lumbar  Three-dimensional finite element  Intervertebral disc  Facet fusion  Range of motion

English Abstract:

  【Abstract】 Objectives: A three-dimensional nonlinear finite element model of L3-L5 based on biomechanical characteristics was established, and to simulate the stress distribution of L4/5 intervertebral disc after the non-fusion and fusion of the bilateral lumbar facet joint of L4/5, also to analyze the L4/5 segment activity. Methods: A 27-year-old healthy adult male volunteer with 175cm height, 70kg weight and no previous history of low back pain was selected. The L3-L5 vertebral two-dimensional image data were obtained by scanning the T12-S1 vertebral body with 64 slice spiral CT. After simplification and smooth processing by Geomagic software, dividing surface and volume meshes by 3-matic software, and assignment by Mimics, the three-dimensional finite element model of lumbar facet joint with non-fusion or fusion was reconstructed finally after importing Ansys software. While the surface anisotropy activity of L5 vertebra constrained, a 500N surface load was given to the top surface of L3 vertebra and a moment of 7.5Nm was exerted to simulate the normal human 7 motion state, including vertical compression, flexion, extension, left and right flexion, left and right rotation. The stress distribution of L4/5 intervertebral disc after non-fusion and fusion, and the L4/5 segment activity was analyzed after operation. Results: The model was established, and the ranges of motion of L3/4 and L4/5 segments were corresponding to previous literatures on lumbar mobility. When compared to the facet non-fusion model, the posterior stress of facet fusion model decreased sharply and the activity of L4/5 segment was significantly reduced in each different motion state, and the difference was statistically significant(P<0.05). Conclusions: Lumbar facet joint fusion can be a good way to reduce the posterior stress of intervertebral disc, to maintain the stability of segment, to avoid the damage of the posterior intervertebral disc and the tear of annulus fibrosus.