Biomechanical Comparison Between Posterior Long-Segment Fixation Short-Segment Fixation and Short-Segment Fixation With Intermediate Screws for the Treatment of Thoracolumbar Burst Fracture A Finite Element Analysis

Abstract

Background: Posterior long-segment (LS) fixation short-segment (SS) fixation and short segment fixation with intermediate screws (SI) have shown good outcomes for the treatment of thoracolumbar burst fractures. However limited data compared the biomechanical properties between LS fixation and SI. The purpose of this study was to compare the von Mises stresses on the pedicular screw system and bone between posterior LS fixation SS fixation and SI for the treatment of thoracolumbar burst fracture. Materials and Methods: The finite element model of thoracolumbar spines from T11 to L3 was created based on the computed tomography image of a patient with a burst fracture of the L1 vertebral body. The models of pedicular screws rods and locking nuts were constructed based on information from the manufacturer. Three models with different fixation configurations梩hat is LS SS and SI梬ere established. The axial load was applied to the superior surface of the model. The inferior surface was fixed. The stress on each screw rod and vertebral body was analyzed. Results: The motion of the spine in SS (0.5 mm) and SI (0.9 mm) was higher than in LS (0.2 mm). In all models the lowest pedicle screws are the most stressed. The stress along the connecting rods was comparable between SI and LS (50 MPa). At the fracture level stress was found at the pedicles and vertebral bodies in SI. There was relatively little stress around the fractured vertebral body in LS and SS. Conclusions: Posterior SI preserves more spinal motion than the LS. In addition it provides favorable biomechanical properties than the SS. The stress that occurred around the pedicle screws in SI was the least among the 3 constructs which might reduce complications such as implant failure. SI produces more stress in the fractured vertebral body than LS and SS which could potentially aid in bone healing according to the Wolff law. Clinical Relevance: SI has proved to be a biomechanically favorable construct and helps preserve the spinal motion segment. It could be an alternative surgical option for treating patients who present with thoracolumbar burst fractures. ? International Society for the Advancement of Spine Surgery.