Determination of thoracic pedicle screw parameters by superior facet in normal adults: an imaging study

doi:10.3969/j.issn.2095-4344.2017.35.008

Abstract

Abstract:

BACKGROUND: In the existing thoracic pedicle screw fixation technique, superior facet or combined with transverse process and the imaginary transverse and sagittal section are used as the reference mark of pedicle screw entry point and angle, respectively, which still remain controversial. Because of the effect of position deviation and subjective judgment during surgery, screw misplacement and severe complications often occur, which limit the clinical application and promotion of the technique. At present, it is very important to select a single bony mark, which is not affected by the patient’s position, and is easy to judge, as the reference mark of screw entry point and angle.

OBJECTIVE: To explore the feasibility of taking superior facet as a single bony mark to determine thoracic pedicle screw parameters in normal adults by measuring 3D reconstruction CT image and it’s corresponding relationships.

METHODS: 3D reconstruction CT images of the thoracic spine in 30 normal adults were selected and the basic parameters, entry angle parameters and entry depth parameters were directly determined on specific reconstructed CT images of T₁-T₁₂.The basic parameters included the vertical distance from the entry point to the midline, the vertical distance from the outer edge of superior facet to the midline and superior facet base width. Entry point parameters were indirectly calculated by the basic parameters, including transversal point-facet distance, entry point ratio and sagittal point-facet distance, which was the horizontal distance from entry point to outer edge of superior facet, the ratio of transversal point-facet distance to superior facet base width, and the longitudinal distance from entry point to the base of superior facet. Entry angle parameters included transversal axis-facet angle and sagittal axis-facet angle, which is the transversal and sagittal angle between the axis of pedicle and the surface of facet. Entry depth parameter included safety screw length, which is the distance from entry point to anterior vertebral cortex along the axis of pedicle. Mean and standard deviation were counted and statistics difference was compared.

RESULTS AND CONCLUSION: (1) Using CT technology of 3D reconstruction, T₁-T₁₂ thoracic transversal section through bilateral pedicle axis, transversal section through the base of the superior facet, which parallel to the bilateral pedicle axis, and oblique sagittal section through homolateral pedicle axis were successfully obtained. (2) The statistical results of the basic parameters were as follows: the left and right vertical distances between T₁-T₁₂ from the entry point to the midline were (14.6±2.6) and (14.5±2.5) mm, the vertical distance from the outer edge of superior facet to the midline were (15.7±1.9) and (15.7±2.0) mm, and superior facet base width were (8.8±1.3) mm and (8.8±1.1) mm, respectively. There was no significant difference in the measured values between two sides of the above parameters (P=0.343, 0.214, 0.467). (3) The statistical results of pedicle screw parameters were as follows: the left and right transversal point-facet distance between T₁-T₁₂ were (1.2±1.3) and (1.3±1.4) mm, entry point ratio were (14.3±17.0)% and (13.6±16.1)%, sagittal point-facet distance were (3.4±0.8) and (3.3±0.9) mm, transversal axis-facet angle were (92.4±4.7)° and (92.6±5.0)°, sagittal axis-facet angle were (91.8±4.1)° and (91.7±3.6)°, and safe screw length were (40.7±4.8) and (40.4±4.6) mm, respectively. There was no significant difference in the measured values between two sides of the above parameters (P=0.073, 0.084, 0.310, 0.265, 0.241, 0.175). (4) These results indicate that taking thoracic superior facet as a single anatomic landmark to determine pedicle screw parameters is simple and feasible in normal adults, and they correlate with each other, which can be used as a new method for choosing screw parameters.

中国组织工程研究杂志出版内容重点：人工关节；骨植入物；脊柱；骨折；内固定；数字化骨科；组织工程

Key words: Thoracic Vertebrae, Bone Nails, Internal Fixators, Tissue Engineering

CLC Number:

R318

Lu Zheng-hao, Li Ji-peng, Zhou Jing-hua, Wang Wei-guo. Determination of thoracic pedicle screw parameters by superior facet in normal adults: an imaging study[J]. Chinese Journal of Tissue Engineering Research, 2017, 21(35): 5622-5629.

Figures/Tables 3

2.2 测量者自身的测量误差进钉点至中线距离的变异系数：右侧为3.6%，左侧为2.9%；上关节突外缘至中线距离的变异系数：右侧为4.1%，左侧为3.7%；上关节突基底宽度的变异系数：右侧为1.8%，左侧为2.6%；横向点突距的变异系数：右侧为4.9%，左侧为4.7%；进钉点比率的变异系数：右侧为4.4%，左侧为4.7%；纵向点突距的变异系数：右侧为2.3%，左侧为3.8%；横向轴突角的变异系数：右侧为1.6%，左侧为2.0%；纵向轴突角的变异系数：右侧为3.1%，左侧为2.2%；螺钉安全长度的变异系数：右侧为4.1%，左侧为4.5%。 2.3 测量者间的误差进钉点至中线距离的变异系数：右侧为2.7%，左侧为3.3%；上关节突外缘至中线距离的变异系数：右侧为4.5%，左侧为4.4%；上关节突基底宽度的变异系数：右侧为2.0%，左侧为1.7%；横向点突距的变异系数：右侧为3.9%，左侧为4.8%；进钉点比率的变异系数：右侧为4.5%，左侧为3.9%；纵向点突距的变异系数：右侧为3.4%，左侧为3.1%；横向轴突角的变异系数：右侧为2.2%，左侧为2.8%；纵向轴突角的变异系数：右侧为1.6%，左侧为2.9%；螺钉安全长度的变异系数：右侧为4.4%，左侧为4.2%。所有变异系数均小于5%，提示测量者自身和测量者之间的误差较小，本组测量精确、可靠。以下数据为2名测量者反复测量3次所得的均值，基础参数的测量结果见表1，置钉参数的测量结果见表2。 2.4 基础参数 2.4.1 进钉点至中线距离 T1-T12左右两侧进钉点至中线距离分别为(14.6±2.6) mm和(14.5±2.5) mm，差异无显著性意义(P=0.343)。除了T2与T12、T3与T10、T4与T9、T5-T8，其余节段间的差异均有显著性意义(P < 0.05)。 2.4.2 上关节突外缘至中线距离 T1-T12左右两侧上关节突外缘至中线距离分别为(15.7±1.9) mm和(15.7±2.0) mm，差异无显著性意义(P=0.214)。除了T1与T2、T4与T9、T5-T8、T10-T12，其余节段间的差异均有显著性意义(P < 0.05)。 2.4.3 上关节突基底宽度 T1-T12左右两侧上关节突基底宽度分别为(8.8±1.3) mm和(8.8±1.1) mm，差异无显著性意义(P=0.467)。除了T2-T8、T10-T12，其余节段间的差异均有显著性意义(P < 0.05)。 2.5 置钉参数 2.5.1 进钉点参数横向点突距：T1-T12左右两侧横向点突距分别为(1.2±1.3) mm和(1.3±1.4) mm，差异无显著性意义(P=0.073)。在T1、T3与T12与其他节段比较，其余节段间的差异均无显著性意义(P > 0.05)。进钉点比率：T1-T12左右两侧进钉点比率分别为(14.3±17.0)%和(13.6±16.1)%，差异无显著性意义(P=0.084)。在T1、T3与T12与其他节段比较，其余节段间的差异均无显著性意义(P > 0.05)。纵向点突距：T1-T12左右两侧纵向点突距分别为(3.4±0.8) mm和(3.3±0.9) mm，差异无显著性意义(P=0.310)。除了T1-T3、T7-T12，其余节段间的差异均有显著性意义(P < 0.05)。 2.5.2 进钉角度参数横向轴突角：T1-T12左右两侧横向轴突角分别为(92.4±4.7)°和(92.6±5.0)°，差异无显著性意义(P=0.265)。除了T3与T12、T4-T11，其余节段间的差异均有显著性意义(P < 0.05)。纵向轴突角：T1-T12左右两侧纵向轴突角分别为(91.8±4.1)°和(91.7±3.6)°，差异无显著性意义(P=0.241)。除了T3-T11，其余节段间的差异均有显著性意义(P < 0.05)。 2.5.3 进钉深度参数螺钉安全长度：T1-T12左右两侧螺钉安全长度分别为(40.7±4.8) mm和(40.4±4.6) mm，差异无显著性意义(P=0.175)。除了T1-T3、T4-T10每相邻两节段、T11-T12，其余节段间的差异均有显著性意义(P < 0.05)。 "

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