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

Jifeng Liu,Huanhuan Wang,Jianmin Lu,Sheng Yang,Chao Chen,Chunyang Xia,Fei Zhou

doi:10.1186/s13018-020-02024-7

Jifeng Liu, Huanhuan Wang + Show 5 more

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https://doi.org/10.1186/s13018-020-02024-7

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Abstract

BackgroundTo 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.MethodsThe 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.ResultsThere 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).ConclusionShort-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.

Highlights

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
With this method, the available reduction of burst fractured vertebra (LSC ≥ 7) and spinal canal decompression can be achieved without laminectomy even if when the spinal stenosis was severe, and it is better than the screw insertion parallel to the endplates, which hardly reduced the intraspinal bone fragments without laminectomy [5, 6]
The axial displacement of the injured vertebrae increased with the increase of the angle during flexion/extension, lateral bending, and rotation, but there was no statistical difference among the four groups (P > 0.05, Fig. 8)

Summary

Introduction

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. Burst fractures of the thoracolumbar spine often require surgical treatment; there is no uniform standard whether the stenotic spinal canal needs decompression or whether the intraspinal retropulsed bone fragments need to be removed for the fracture combined with nerve injury [1,2,3]. Short-segment Schanz screw fixation implanted in an oblique downward direction can achieve an upward and forward reduction of the anterior column, middle column, and the posterior column, resulted in a better reduction of the downward and backward retrodisplaced vertebra With this method, the available reduction of burst fractured vertebra (LSC ≥ 7) and spinal canal decompression can be achieved without laminectomy even if when the spinal stenosis was severe, and it is better than the screw insertion parallel to the endplates, which hardly reduced the intraspinal bone fragments without laminectomy [5, 6]

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