The feasibility of short-segment Schanz screw implanted in an oblique downward direction for the treatment of lumbar 1 burst fracture: a finite element analysis

Background To evaluate the biomechanical properties of short-segment Schanz screw implanted in an oblique downward direction for the treatment of lumbar 1 burst fracture using a finite element analysis. Methods The Universal Spine System (USS) fixation model for adjacent upper and lower vertebrae (T12 and L2) of lumbar 1 vertebra burst fracture was established. During flexion/extension, lateral bending, and rotation, the screw stress and the displacement of bone defect area of the injured vertebrae were evaluated when the downward inserted angle between the long axis of the screws and superior endplate of the adjacent vertebrae was set to 0° (group A), 5° (group B), 10° (group C), and 15°(group D). There were 6 models in each group. Results There were no significant differences in the maximum screw stress among all the groups during flexion/extension, lateral bending, and rotation (P > 0.05). There were no significant differences in the maximum displacement of the bone defect area of the injured vertebrae among all the groups during flexion/extension, lateral bending, and rotation (P > 0.05). Conclusion Short-segment Schanz screw implanted in an oblique downward direction with different angles (0°/parellel, 5°, 10°, and 15°) did not change the maximum stress of the screws, and there was a lower risk of screw breakage in all groups during flexion/extension, lateral bending, and rotation. In addition, the displacement of the injured vertebra defect area had no significant changes with the change of angles.