Analysis Of The Influence Of Lumbar Decompression On The Stress Distribution Of Different Grades Of Disc Degeneration Using The Finite Element Method

BackgroundA large number of biomechanical study confirmed that lumbar decompression and fusion may lead to changes in biomechanical properties and promote the accelerated degeneration of the adjacent segment; However, little literature on the influence of lumbar decompression on the stress distribution of adjacent disc degeneration was found.ObjectivesTo investigate stress distribution of nucleus pulposus and annulus fibrosus matrix in different grades of disc degeneration after discectomy and posterior laminectomy using the finite element method(FEM).MethodsThree FEMs of lumbar spinal segment (L3-L5) in different grades of disc degeneration(healthy,mild,moderate and severe) were established:intact spine, L4-L5 left discectomy and L4-L5 total laminectomy. According to in vitro test methods, every model was loaded with pure moments of 10-Nm in the three main anatomic planes and with axial preload of 400N. The bottom of the L5 vertebral body was fixed. The range of motion (ROM) of L3-L5 segment,von Mises stress in the nucleus pulposus and annulus fibrosus matrix of L3-L4 disc were investigated.ResultsCompared to healthy disc, the mildly degenerated disc indicated an increase of range of motion in the intact spine and decrease in the other disc degeneration. The range of motion of left bending and flextion increased in L4-L5 left discectomy model and in L4-L5 total laminectomy respectively. Both L4-L5 left discectomy and L4-L5 total laminectomy model indicated an increase of range of motion of axial rotation. The von Mises stress of the nucleus pulposus increased in the mildly degenerated disc and moderately degenerated disc. The von Mises stress of the nucleus pulposus in the severely degenerated disc decreased compared to the other grades,but was still higher than that of healthy disc. The mildly degenerated disc indicated an increase of the von Mises stress in annulus fibrosus matrix. The stress in the annulus fibrosus matrix was also increased in the L4-L5 left discectomy model during left bending motion. The axial stress was higher in the L4-L5 total laminectomy than in the L4-L5 left discectomy.ConclusionsThe results support different lumbar spine decompression contribute to stress distribution changes in the different grades of disc degeneration. This result is also useful in the future clinical work.