[Anatomic study of the posterior laminar screw fixation on C7]

To measure anatomic data of laminar of C7 and evaluate the possibility of the placement of C7 laminar screw.

Twenty-two specimens of C7 were measured with an vernier caliper and a goniomete and finded out the anatomic data for prominent vertebra laminar screw placement. The indicators included the thickness of the superior, median and inferior part of C7 laminar (T1, T2, T3), the height of the laminar(H), the distance of the anchor point to the medial wall of C7 pedicle and the lateral wall of the lateral mass (L1, L2) and the angle between the axis of C7 lamina and sagittal plane(alpha).

The mean thickness of superior part of C7 lamina (T1) was (4.30 +/- 0.27) mm, (5.32 +/- 0.27) mm in median part (T2) with 27% (6 cases) of specimens thickness less than 4.50 mm and (4.78 +/- 0.26) mm in inferior part (T3). Both median part and inferior part were thicker than 4.50 mm. The mean height of C7 laminar (H) was (14.83 +/- 0.26) mm. The distance from the laminar anchor point to the medial wall of C7 pedicle (L1) and the lateral wall of the lateral mass (L2) was (26.99 +/- 0.48) mm and (41.60 +/- 1.10) mm respectively. The mean angle between the axis of C7 laminar and sagittal plane(alpha) was (49.3 +/- 1.1) degrees.

It is feasible to place screw in C7 laminar and this technique can be applied in 73% of Chinese. Compared with C7 pedicle screw technique, this technique is simple with little risk to the nerve and vascular structures.