<p><b>OBJECTIVE</b>To explore the location of the anterior border of facets and the posterior border of vertebral bodies in lower cervical spine,and to provide a quantitative data to evaluate the correct length of transarticual screws in lower cervical spine during procedure.</p><p><b>METHODS</b>One hundred standard lateral X-ray films and fifty CT films on cervical spine were used to measure the distance of the anterior border of facets and the posterior border of vertebral bodies in lower cervical spine. HS, HM and HI were defined as parameters, which means the distance between the anterior border of the superior (HS), median (HM) and inferior (HI) part of facets and the posterior border of corresponding vertebral bodies. The value will be negative if the anterior border of the facet located before the vertebral body.</p><p><b>RESULTS</b>'HS > HM > HI' was found in all facets in lower cervical spine. The anterior border of the facet in C(3,4) located before the posterior border of the vertebral body of C3. The anterior border of C(4,5) and C(5,6) was inclined to posterior. The anterior border of C(6,7) located after the posterior border of the vertebral body of C6. The pattern of HS increased from C(3,4) to C(6,7), the minimal (0 +/- 0.25) mm and the maximal (2.91 +/- 1.05) mm. The tendency of HM raised from C(3,4) to C(6,7), the minimal (-1.57 +/- 0.53) mm and the maximal (1.54 +/- 0.39) mm. The pattern HI added from C(3,4) to C(6,7), the minimal (-2.03 +/- 0.40) mm and the maximal (1.08 +/- 0.70) mm.</p><p><b>CONCLUSION</b>During the implantation of the transarticular screws, the tip of the screws should be 0-2 mm before the posterior border of the vertebral body of C3 at C(3,4), 0-2 mm after that of C4 at C(4,5), 0.5-2.5 mm at C(5,6) and 1-3 mm at C(6,7). The quantitative location between the anterior border of facets and the posterior border of the corresponding vertebral bodies can offer an indirect method to evaluate the correct length of transarticual screws in lower cervical spine during procedure.</p>