Cadaveric study on axis anatomic landmark featured by the junction between lateral border of inferior articular process and posterior branch of transverse process for C2 pedicle screw fixation

English Keywords:Axis  Pedicle screw fixation  Anatomy

English Abstract:

  【Abstract】 Objectives: To describe the feasibility of C2 pedicle screw fixation by means of axis anatomic landmark confirmed by the junction between lateral border of inferior articular process and posterior branch of transverse process, and to provide a reference for its clinical practice. Methods: Morphometric measurements and radiological techniques were implemented in 30 adult embalmed cadaveric specimens. The junction between lateral border of inferior articular process and posterior branch of transverse process in axis was exposed to serve as anatomic landmark. The entry point of C2 transpedicular screw fixation was determined as 1-2mm lateral to the crossing point of two lines, a horizontal line through the anatomic landmark, and a vertical line through the midpoint of distance from the junction of pedicle medial and lateral border to lateral mass. The next five anatomic parameters were measured separately,including the width of posterior branch of transverse process, the distance from entry point to anatomic landmark, C2 nerve root, the inner and inferior wall of transverse foramen, the medial wall of vertebral canal. Finally, the total of 60 pedicle screws were inserted at the entry point with an angle of 25°-30° medial to the sagittal plane and 20°-25° superior to the axial plane. A 3-dimensional computed tomogram was checked ostoperatively to evaluate screw placement and to verify its angulation. Results: No statistical differences were found in all of anatomic parameters and screw angulations between left and right side(P＞0.05). Therefore, the overall mean data were gained by means of bilateral summation. The overall mean width of posterior branch of transverse process was 5.13±0.15mm. The overall mean distance from entry point to anatomic landmark, C2 nerve root, transverse foramen and vertebral canal was 5.73±0.62mm, 4.04±0.21mm, 5.32±0.49mm and 4.94±0.38mm respectively. The averaged screw angles specified as 28.4°±3.1° medially and 22.5°±2.9° superiorly. There were four screws shown to extend into transverse foramen and vertebral canal. The incidence of screw malposition was 6.7%(4/60). Moreover, four screws excess over the length of pedicle. Conclusions: The study shows that anatomic landmark stated above has definite assistance in locating the C2 entry point to achieve pedicle screw fixation. However, there still be a potential of screw malposition due to anatomic variation.