The anatomic study on the feasibility of posterior pedicle screw fixation on atlas

Objective: To study the feasibility of posterior pedicle screw placement on atlas. Methods: with an electronic digital caliper, 50 dry atlas specimens were used to measure the dimension of lateral mass, pedicle and posterior arch. Results: The mean width and height of the mid-portion of the C 1 lateral mass were 12.78 mm and 12.95 mm, and that of the C 1 pedicle were 8.57 mm and 5.83 mm,respectively. The mean width of C 1 posterior arch under the vertebral artery groove was 8.46 mm, and the height of this portion, 3.88 mm for medial one-third and 4.25 mm for lateral one third. Conclusions: It is possible to insert a pedicle screw on atlas, and the thickness of C 1 posterior arch under the vertebral artery groove was the main restrictive and decisive factors for C 1 pedicle screw placement.