An understanding of the anatomical relationships of the lateral masses of the cervical spine is very important to achieve proper screw placement. Since the surgeon visualizes only the posterior aspect of these masses, those structures that are immediately anterior to them are of prime concern when the screws are placed. The lateral mass (articular pillar) is the bulky lateral extension of the lamina and is connected to the vertebral body through the pedicles in an antero medial direction (Figs 1.1A and B).
The transverse process, which harbors the foramen transversarium in its medial part, is connected to the vertebral body through a thin strut. It is also connected to the lateral mass through a relatively thicker bony portion (Fig. 1.2). The lateral masses are called articular pillars (Fig. 1.3A), since the superior and the inferior articular processes are formed from these masses(Figs 1.3B and C).
The superior facets are usually not seen from 5posterior. Superior articular facet is oriented 35 degrees in sagittal plane; it increases gradually to 55° at C7 (Fig. 1.4).
The lateral masses of the C7 vertebra are relatively thinner than the other cervical vertebrae.
The margins of the lateral masses are defined superiorly and inferiorly by the facet joints, laterally by the extreme edge of the mass and medially by the lateral margin of the lamina (Fig. 1.5). The center point of the mass (Hillock) is the highest point and coincides with the summit of the facet.(Fig. 1.6).
The vital structures, the vertebral artery traveling through the foramen transversarium and the cranial nerve roots emerging from the spinal canal through the intervertebral foraman, are placed anterior to the lateral masses and are not seen from behind (Fig. 1.7).