Anatomic and clinical evaluation of the location relation between C1 pedicle and C_2 lateral mass / 中华骨科杂志

ABSTRACT

Objective To study the relevant position of atlas pedicle to axis lateral mass, set up a technique of C1 pedicle screw placement with the lateral mass of axis as an anatomic landmark, and evaluate the reliability of the present screw placement technique by clinical practice. Methods 50 paired atlas and axis specimens were used to measure the distance from the sagittal midline to the medial border, the midpoint (the middle point of the mediolateral border) and the lateral border of C1 pedicle and C2 lateral mass. Furthermore, the distance between the medial border of C1 pedicle and that of C2 lateral mass, the distance between the midpoint of C1 pedicle and that of C2 lateral mass and the distance between the lateral border of C1 pedicle and that of C2 lateral were calculated respectively. The technique of C1 pedicle screw fixation was established. Using the present landmark technique, C1 pedicle screws were placed in 6 patients of atlantoaxial instability, including 5 males and 1 female averaged 41 years old, with os odontoideum in 1, odontoid hypoplasia in 3, and old odontoid fractures in 2. Results The medial border, the midpoint and lateral border of C1 pedicle was averaged (1.37?0.51) mm, (1.60?0.61) mm and (2.15?0.60) mm medial to C2 lateral mass, respectively. The entry point of C1 pedicle screw in present technique was defined as the method of making a vertical line through the midpoint of C2 lateral mass, and the entry point was 3 mm under the cross point of the superior rim of C1 posterior arch with the vertical line. 12 C1 pedicle screws were placed exactly in all 6 patients, and no neural or vascular injury was observed. The postoperative radiographs and CT scans verified all of C1 screws with a good position. Conclusion There is a steady anatomic relation between C1 pedicle and C2 lateral mass, the C2 lateral mass could be as a convenient anatomic landmark to determine the location of C1 pedicle and the position of C1 pedicle screw entry point.