Quantitative anatomy of the cervical facet and the posterior projection of its inferior facet.

For this study, 41 cervical spines from C3 to C7 were directly evaluated. Anatomic evaluation of the cervical superior and inferior facets included the facet height, width, and angulation relative to the coronal plane. The projection of the inferior facet on the posterior aspect of the lateral mass was constructed and measured, and the dimensions of the lateral mass were evaluated. In general, the male linear parameters were larger than the female parameters, but the male angular dimensions were smaller than those of females. The posterior projection height of the inferior facet was found to be 7.4-9.0 mm from C3 to C7 for both sexes and was approximately 2 mm larger than half the height of the lateral mass. C6 and C7 had relative larger superior and inferior facet angles. The lateral mass was thinner at the level of C6-7. This study indicated that there may be a risk of violating the inferior articular facet and the related superior articular facet of the most caudal facet joint if a screw starting at the midpoint or below the midpoint of the lateral mass is directed perpendicular to the posterior aspect of the lateral mass at the level of C3-7.