CT Based Anatomical Evaluation of Pre Vertebral Structures With Respect to Vertebral Body Using a Clock Face Analogy
Study Design. Retrospective Chart and CT Scan Review Objective. To define the relationship of the pre vertebral structures for each level to assist in easier intraoperative visualization. Summary of Background Data. Vascular and visceral injuries from pedicle screws are well known. This study will define the relationship of the pre vertebral structures for each level to assist in avoiding potential complications. Methods. Pre and post operative CT scans were reviewed to define the pre vertebral structures in relation to a clock face. On reformatted axial slices, a clock face was superimposed so that the left transverse process (TP) represented 8 o'clock and the right TP represented 4 o'clock. The positions of the TP on the clock face did not change with rotation of the vertebra. Results. 108 patients had pre operative CT scans. 78 had post operative CT scans. Median age was 15 years, median Cobb angle was 50deg, fused were 12, with 21 fixation points. 6324 axial CT slices were reformatted and analyzed. The trachea was located at 12 o'clock at T1, 1 o'clock at T2 T4, and between 12 and 1 o'clock at T5. The esophagus starts as a midline structure at 12 o'clock from T1 T2, moves to 11 o'clock from T3 T6, and further to 10 o'clock from T7 T9. The aorta starts at 10 o'clock at T5 T6, moves left at T7 T8 to 9 o'clock, and returns to 10 o'clock from T9 T11. It appears at 11'clock at T12, and at 12 o'clock from L1 L4. In about a third of cases, it is at 1 o'clock from L1 to L4, where it bifurcates. Conclusions. This CT based anatomical study provides a simple reference frame to help surgeons visualize the vital structures at each level. This three dimensional visualization is facilitated by fixing the position of TP on the clock face. Knowledge of this anatomical relationship can help avoid direct injury, and is easier to recall intra operatively. Level of Evidence: 3
Spine