Comparison of biomechanical properties of single-segment and two-segment fusion for Denis type B spinal fracture / 中华骨科杂志

ABSTRACT

Objective To compare the biomechanical properties of single-segment and two-segment fusion for Denis type B spinal fracture.Methods Two female patients with Denis type B L1 vertebral fracture were enrolled in this study.The 45-year-old patient (Frankel B) underwent posterior reduction and fixation with pedicle screw system plus anterior two-segment fusion and the 41-year-old patient (Frankel C) underwent posterior reduction and fixation with pedicle screw system plus anterior one-segment fusion.The intervertebral fusion was achieved in both patients 1 year after operation.CT data of the two patients at 1 year after surgery was collected,including data of 41-year-old patient before and after removal of pedicle screws and data of 45-year-old patient without removal of pedicle screws.These three sets of data were imported into the Mimics software to establish T11-L2 three dimensional models.After construction of the models,they were imported into ANSYS software.An axial load (260 N) and 10 Nm torque were loaded to simulate the flexion,extension,lateral bending and rotation of the spine,respectively.Meantime,under above 6 kinds of motion form,the average displacement of the spine and the average Von Mises stress of T11-12 intervertebral disc were recorded and compared.Results There was no significant difference in the average displacement of the spine between two-segment fusion patient and single-segment fusion patient without removal of pedicle screws.However,under all motion forms,the average displacement of the spine of single-segment fusion patient after removal of pedicle screws was significantly higher than that before removal of pedicle screws and that of two-segment fusion patient.The average Von Mises stress of T11-12 intervertebral discs of two-segment fusion patient was significantly higher than that of one-segment fusion patient.Moreover,the average Von Mises stress of T11-12 intervertebral discs of single-segment fusion patient before removal of pedicle screw was higher than that after removal of pedicle screw.Conclusion Under the premise of satisfactory interbody fusion,removal of pedicle screws after one-segment fusion can increase spinal motion,reduce the stress of the adjacent intervertebral discs and delay disc degeneration.