Impact of cement-augmented pedicle screw instrumentation on adjacent segments degeneration in single or double-level lumbar spinal fusion: a finite element analysis

English Keywords:Lumbar instrumentation  Pedicle screw  Cement-augmented  Adjacent segments degeneration  Finite element analysis

English Abstract:

  【Abstract】 Objectives: To compare the impact of pedicle screw(PS) fixation and cement-augmented pedicle screw(CAPS) fixation on adjacent segment degeneration(ASD) in single or double segment posterior lumbar fusion. Methods: An intact finite element model of L3-S1 segment was established by using CT scan data of a normal male volunteer. After verifying the validity of the intact model, the solid and fenestrated pedicle screws were scanned by a three-dimensional scanner to construct the screw models. Then, the PS fixation and CAPS fixation models were established respectively. A 400N vertical axial pre-load was imposed on the L3 superior surface and a 7.5N·m moment was also applied on the L3 superior surface to simulate 6 different physiological motions: flexion, extension, left bending, right bending, left rotation, and right rotation. The differencesof intervertebral disc/facet joint Von Mises stress and range of motion(ROM) on adjacent segments were compared between the models. Results: The validity study showed that the ROM of the intact model in all directions was similar to previous cadaveric studies. In single-level lumbar spinal fusion group, the intervertebral disc and facet joint Von Mises stress and ROM on adjacent segment were slightly lower in PS group than in CPAS group. In double-level lumbar spinal fusion group, the intervertebral disc and facet joint Von Mises stress and ROM on adjacent segment were lower in PS group than in CPAS group. The stress distributions of intervertebral disc on adjacent segments were similar in the two lumbar instrumentation groups, which were mainly on the edge of annulus fibrosus. Conclusions: The biomechanical analysis showed that, CAPS could increase ROM and stress of adjacent segment when compared with CPS, especially in double-level segments fusion, which might accelerate the adjacent segment degeneration.