Cortical Bone Trajectory Screw Fixation in the Upper and Middle Thoracic Spine (T1-T8): An Anatomic and Radiographic Assessment

Abstract

To assess an alternative method of cortical bone trajectory (CBT) screw placement in the thoracic spine from T1 to T8 and to investigate the proper entry point, screw insertion angle, screw length, and diameter. Computed tomography images of 80 patients were used to measure all related parameters. Ten cadaveric spines were studied and 4.5-mm screws were inserted into both sides of the vertebrae. Computed tomography of all vertebrae previously inserted with CBT screws was performed and lateral or medial pedicle wall violation was checked. Of the inserted 160 CBT screws, 41.25% (66/160) penetrated the lateral pedicle wall, and the proportion of medial pedicle wall violation accounted for 0.625% (1/160). Maximal screw length tended to gradually increase from T1 to T8 (from 24.54 mm at T1 to 29.53 mm at T8). Compared with T4 and T5, maximal screw diameters of other thoracic levels were wider, ranging from 4.63 mm at T4 to 5.53 mm at T8. The greatest lateral angle was 8.66° in men and 8.39° in women at T8, whereas the smallest lateral angle was 4.97° in men and 4.67° in women at T1. The cephalad angle ranged from 17.23° at T7 to 31.50° at T1 and it was significantly larger in men at T7 (P < 0.05), T6 and T8 (P < 0.01). Based on the results of this study, we suggest that patients could be placed with 4.5× 25.0-30.0 mm CBT screws from T1 to T8 through the pedicle or pedicle rib unit.