Biomechanical Comparison of Corticopedicular Spine Fixation versus Pedicle Screw Fixation in a Lumbar Degenerative Spondylolisthesis Finite Element Analysis Model

Objective To compare the stability of a corticopedicular posterior fixation (CPPF) device to traditional pedicle screws for decompression and fusion in adult degenerative lumbar spondylolisthesis. Methods Finite element analysis (FEA) was used in a validated model of grade 1 L4-L5 spondylolisthesis to compare segmental stability following laminectomy alone, laminectomy with pedicle screw fixation, or laminectomy with CPPF device fixation. A 500N follower load was applied to the model and different functional movements were simulated by applying a 7.5Nm force in different directions. Outcomes included degrees of motion, tensile forces experienced in the CPPF device, and stresses in surrounding cortical bone. Results At maximum loading, laminectomy alone demonstrated an 1° increase in flexion range of motion from 6.35° to 7.39°. Laminectomy with pedicle screw fixation and CPPF device fixation both reduced spinal segmental motion to ≤1° at maximum loading in all ranges of motion, including flexion (0.94° and 1.09°), extension (-0.85°and -1.08°), lateral bending (-0.56° and -0.96°), and torsion (0.63°and 0.91°), respectively. There was no significant difference in segmental stability between pedicle screw fixation and CPPF device fixation during maximum loading with a difference of ≤0.4° in any range of motion. Tensile forces in the CPPF device remained ≤51% the ultimate load to failure (487N) and stress in surrounding cortical bone remained ≤84% the ultimate stress of cortical bone (125.4 MPa) during maximum loading. Conclusion CPFF fixation demonstrated similar segmental stability to traditional pedicle screw fixation while tensile forces and stress in surrounding cortical bone remained below the load to failure.