Abstract
PurposeTo explore the feasibility of sacral-2-alar (S2-alar) screw placement by measuring the length, diameter, and angle of the screw trajectory on computed tomography (CT).MethodsThis study selected 100 Han-nationality adults in northern China with a normal spine and pelvis. CT data were imported into PHILIPS software for reconstructing the 3D digital images. The optimal S2-alar screw trajectory was imitated on CT. Parameters including the length of the screw trajectory, sagittal angle, coronal angle, distance between the entry point and the spinous process, and minimum diameter of the screw trajectory were measured to evaluate the application of S2-alar screws.ResultsIn total, 48 males and 52 females were included. The average length of the left screw trajectory was 47.18 ± 3.91 mm. The sagittal angle was 29.06 ± 4.00°. The coronal angle was 13.31 ± 6.95°. The distance between the entry point and the spinous process was 21.0 (3.7) mm. The minimum diameter of the screw trajectory was 17.1 (2.3) mm. The average length of the right screw trajectory was 45.46 ± 4.37 mm. The sagittal angle was 23.33 ± 4.26°. The coronal angle was 14.88 ± 6.84°. The distance between the entry point and the spinous process was 22.8 (2.9) mm. The minimum diameter of the screw trajectory was 16.9 (3.1) mm. In women, the average length of the left screw trajectory was 44.80 ± 3.66 mm. The sagittal angle was 32.14 ± 5.48°. The coronal angle was 16.04 ± 7.74°. The distance between the entry point and the spinous process was 21.8 (2.8) mm. The minimum diameter of the screw trajectory was 17.1 (5) mm. The average length of the right screw trajectory was 44.01 ± 3.72 mm. The sagittal angle was 25.12 ± 5.19. The coronal angle was 16.67 ± 8.34°. The distance between the entry point and the spinous process was 21.6 (2.7) mm. The minimum diameter of the screw trajectory was 17 (4.5) mm. As seen from the data, there were significant differences in the minimum diameter of the screw trajectory in both males and females. In females, there were also significant differences between the left and right sides in the coronal angle. Between males and females, there were statistically significant differences in the length of the screw trajectory. There were no statistically significant differences in the other parameters between males and females.ConclusionThe optimal screw trajectory of the S2-alar screw can be found on CT. The length and deflection angle of the screw meet the clinical requirements. This method is easy to perform and feasible for clinical application.
Highlights
IntroductionIn the treatment of moderate-severe lumbar spondylolisthesis and degenerative scoliosis deformity, standalone sacral-1 (S1) screws have a higher rate of fixation failure
Lumbosacral fusion procedures have been widely used in clinical practice
We found that the S2-alar screw trajectory became longer when the screw was placed on the sides of the sacral wings and had a larger angle in the sagittal plane
Summary
In the treatment of moderate-severe lumbar spondylolisthesis and degenerative scoliosis deformity, standalone sacral-1 (S1) screws have a higher rate of fixation failure. This is because (1) the stress of the distal screw is large; (2) the pedicle of the S1 vertebral. The clinical application of conventional sacral-2-alar (S2-alar) screws is limited due to their weaker pullout resistance. We found that the S2-alar screw trajectory became longer when the screw was placed on the sides of the sacral wings and had a larger angle in the sagittal plane. Prolongation of the bony screw trajectory correspondingly increases the pullout resistance and, in turn, has the effect of enhanced distal fixation. We measured the clinical data of Chinese S2-alar screws by computed tomographic (CT) scans to provide the basis for clinical application
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