Lordotic Influence of Pedicle Screw Fixation on the Initial Stability of a Single Spinal Motion Segment with an Anterior Interbody Cage

Circumferential lumbar fusion using an interbody cage and pedicle-based screw fixation is particularly indicated for complex lumbar spinal lesions involving major instability, flatback deformity, and failed disc surgery to restore lumbar lordosis and provide a high union rate with acceptable functional outcomes. To test the complementary efficacy of polyaxial pedicle screw on the anterior interbody cage, a biomechanical testing was performed on a simulated single-level spinal fusion model under a compressive flexural load to measure various parameters including construct stiffness, rod strain, cage strain, and percentage of the contact area between the interbody cage and vertebrae. This synthetic polyethylene model was posteriorly instrumented with polyaxial or monoaxial pedicle screws, also linked with the connecting rods at 0∘,7∘,14∘and 21∘sagittal contours, to compare the effects of different sagittal alignments on each construct. For each subgroup, either a wedge-shaped interbody cage was placed anteriorly or no cage was used in order to determine its supportive role on the construct. When an anterior interbody cage was added in the monoaxial pedicle screw group, there were significant differences in construct stiffness among various patterns of the contoured rods. However, in the polyaxial pedicle screw group, the addition of interbody cage increased the whole construct stiffness with only minor differences among all patterns of the contoured rods. A significant correlation of percentage of the contact area emerged between the vertebrae and an interbody cage under the lordotic influence of posterior pedicle-based screw designs and various rod contours. Also, interbody cage strain was inversely related to rod strain. Polyaxial screw fixation produced nearly equal percentages of the contact area among all constructs with different sagittal alignments, and optimized the initial stabilization effect of the interbody cage for preserving lumbar lordosis and intervertebral disc height.

並列關鍵字

interbody cage ； pedicle screw ； synthetic model ； contoured rod ； lumbar lordosis

國際替代計量

全文下載

主題瀏覽