Introduction. To introduce a new classification method and analyze related risk factor about lateral wall perforation associated with lower cervical pedicle screw and free-hand insertion technique. Methods. A Retrospective study was made to analyze 214 patients (1024 screws) with various cervical spine disorders, involved in pedicle screw instrumentation at C3-7 from July 2004 to July 2009. Researchers assessed the position of the screws in the pedicle by carefully probing intraoperatively and studying postoperative thin-slice computed tomography scan. Perforation of lateral wall was classified into two phases. Phase I refers to the burst of the pedicle by screw, which means that the length of screw threads penetrating the external cortex of pedicles on CT scan is 2 mm, whereas in Phase, the length is >2 mm. The Penetrated screws and related factors were analyzed though Backward Stepwise (Wald) Logistic regression. Results. During the follow-up, 2 screws were reported to be broken and 1 screw loosened. Of the screws inserted, total of 129 screws 12.60% have shown violated of lateral pedicle walls, included 101 screws (9.86%) causative of Phase I and 28 screws (2.73%) of Phase II. Two variance were deduced in the regression analysis, which concerned to ratio variance between inner and lateral walls, PRC 0.695, OR value = 2.003and angle difference variance between screws implanted and measurements preoperativePRC −1.542, OR value = 0.214). Conclusions. Free-hand lower cervical pedicle screw insertion in this series was comparatively safety. Phase I Penetration was believed to be safe of
