Biomechanical Evaluation of Cortical Bone and Traditional Trajectories for Lumbar Single Level Segment Fixation

Abstract Background: The aim of this study was to evaluate the biomechanical stability of a lumbar internal fixation system with 3 different fixation techniques by the establishment of a three-dimensional finite element (FE) model of lumbar single level fixation.Methods: A three-dimensional osseoligamentous nonlinear FE model of osteoporosis lumbar 4-5 (male, aged 57 years, height 170 cm, weight 70 kg, bone mineral density T value -2.8SD) was built to detect the biomechanical stability of an internal fixation system with the following 3 screw trajectories: traditional pedicle screw trajectory fixation (TT), cortical bone trajectory (CBT) screw and hybrid pedicle screw fixation (CBT + TT). The location and area of maximal equivalent stress and the angular displacement of this lumbar model with different screw trajectories were measured in anterior bending, posterior extension, lateral bending and during rotation.Results: The angular displacement of this lumbar model with the 3 different screw trajectories was similar, all of which could restrict the angular displacement of lumbar vertebrae. The maximal equivalent stress was located at the border of the CBT screw and rod, with the hybrid screw fixation technique in axial rotation. Conclusion: The use of CBT and TT screws in lumbar internal fixation had similar stability. The CBT screw could be an alternative solution to lumbar short-segmented fixation, but temporary immobilization would be required to avoid the failure of CBT screw fixation due to the increasing stress in position of extensive lateral bending and rotation.