[The anatomical feasibility analysis of posterior laminar screw fixation techniques in upper thoracic vertebrae]

To investigate the anatomical feasibility and the technique of T(1)-T(3) crossing laminar screws fixation in the adult population.

There were 33 dry upper thoracic vertebras specimen which included respectively T(1), T(2), T(3) were studied. Spinous process height (Hs), bilateral laminar height (H), length of superior laminar screws (Ls), length of inferior laminar screws (Li), bilateral thickness of laminar (TL) and crossing angle the laminar (A) were measured. On the basis of modified Kretze's technique, T(1) crossing laminar screws implantation was performed under visual control. The crossing laminar screws position were evaluated by X-ray and visualizing.

The mean Hs of T(1) was the highest which was (15.7 ± 1.6) mm; the mean H of T(3) was the highest which was (18.7 ± 1.1) mm; the TL and A of T(1) were (6.3 ± 0.9) mm and 101.8° ± 4.5°, that of T(2) were (6.9 ± 1.0) mm and 101.9° ± 4.3°, that of T(3) were (6.5 ± 0.9) mm and 102.9° ± 4.4°, respectively. There were no significant differences between the values of the H and TL on left and right sides (P > 0.05). The Ls of T(1), T(2), T(3) were shorter than Li of that [(31.7 ± 2.4) mm vs. (37.3 ± 2.3) mm, (25.8 ± 2.2) mm vs. (32.3 ± 2.7) mm, (25.3 ± 2.7) mm vs. (31.2 ± 2.9) mm, respectively]. There was significant statistically difference between the values of the Ls and Li on the same vertebra (P < 0.05). The mean TL of T(2) was the thickest, which was significant statistically thicker than that of T(1) (t = 8.876, P < 0.01), which was not significant statistically thicker than that of T(3) (t = 1.919, P > 0.05). The T(1) crossing laminar screws were successfully placed, without impingement of the spinal canal.

It is feasible to place T(1), T(2), T(3) crossing laminar screws in most people. This study provides anatomic guidelines to allow for accurate screw selection and insertion.