Three-dimensional finite element analyses of unilateral pedicle screws fixation in lumbar spine

English Keywords:Lumbar spine  Finite element model  Pedicle screw  Unilateral fixation  Lumbar fusion

English Abstract:

  【Abstract】　Objective：To construct a normal L3-L5 spinal segment model by using finite element method and investigate the biomechanical characteristics of unilateral pedicle screws fixation.Method：A three-dimensional finite element model of an intact L3-L5 segment was constructed by using computed tomography scans of a healthy male.The commercially available finite element program Geomagic Studio 9.0，Simpleware　2.0 and Abaqus 6.7 were applied to model.Based on the intact L3-L5 model（INT），new models were generated by simulating unilateral pedicle screws fixation and posterolateral fusion model（M1），unilateral pedicle screws fixation with a single cage insertion model（M2），and bilateral pedicle screws fixation with a single cage insertion model（M3）.500N preload was added on the superior surface of the L3 vertebral body，followed by load of 10N·m torque to simulate L4/5 flexion-extension，lateral bending and axial rotation，the L4/5 angular variation and stress distribution in pedicle screw and cage under different load were documented.Result：The angular variation in M1，M2，and M3 decreased significantly compared with normal，the angular variation in M3 showed similar with that in M2 under all direction except right lateral bending and extension，and M1 showed less stability under lateral bending and axial rotation.The pedicle peak stress in M1 was markedly higher than that in M2 and M3，especially high on left lateral bending and extension.The pedicle peak stress in M2 was markedly higher than that in M3，and the cage peak stress in M2 was higher than that in M3 on all direction.Conclusion：Unilateral pedicle screws fixation cannot provide sufficient stability in lateral bending and axial rotation，pedicle screws endure more stress.Unilateral pedicle screws plus cage instrumentation can restore the stability as well as share the stress of pedicle screws.