RESUMEN
<p><b>OBJECTIVE</b>To evaluate the screw pull-out strength of posterior C2 when the screw is fixed to C2 through the trans-pedicle or lateral mass or trans-laminar unicortically or bicortically,so as to provide biomechanical basis for the clinical application of posterior C2 screw fixation technique.</p><p><b>METHODS</b>The pedicle screw,the lateral mass screw or the laminar screw was separately anchored into 30 fresh C2 specimens unicortically or bicortically. The screw pull-out strength of different fixation was tested and compared with the others.</p><p><b>RESULTS</b>The average pull-out strength of C2 bicortical pedicle screw was (1255.8 +/- 381.9) N, the strongest during all the methods. The mean pull-out strength of C2 unicortical pedicle screw, C2 bicortical lateral mass screw and C2 bicortical laminar screw were (901.8 +/- 373.3) N, (776.1 +/- 306.8) N and (640.8 +/- 302.9) N respectively,with no statistical difference.</p><p><b>CONCLUSION</b>Pedicle screw should be the first choice for the posterior fixation on axis. C2 lateral mass screw fixation and C2 laminar screw fixation can be another supplement choice and the screw had better be placed bicortically.</p>