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-T12thoracic 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-T12from 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-T12were (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.