Atlas or C1 Vertebra, Posterior View

Description

Positioned at the craniovertebral junction, the atlas (C1) is highlighted in posterior view as a bony ring composed of anterior and posterior arches joined by thick lateral masses. Along the superior surface of the posterior arch, the sulcus arteriae vertebralis forms a distinct groove just medial to the posterior tubercle, marking the course of the vertebral artery as it turns toward the foramen magnum. Inferior to C1, the axis (C2) is identifiable by the dens projecting superiorly, while C3 through C7 align caudally with their spinous processes and transverse foramina arranged in a regular cervical column. No vertebral body at C1. Posterior anatomy of the atlas matters because the vertebral artery and accompanying venous plexus are exposed to injury at this segment during posterior C1 instrumentation, suboccipital decompression, and C1 lateral mass screw placement. The relationship between the posterior arch, lateral mass, and the vertebral artery groove helps clarify why an anomalous ponticulus posticus (arcuate foramen) can complicate screw trajectories and has been linked to cervicogenic headache and vertebrobasilar insufficiency in select cases. This view also reinforces the biomechanics of the atlantoaxial complex, where C1 rotates around the dens and stabilizing ligaments, a common site of instability in trauma and in rheumatoid arthritis. Educators can place this figure into gross anatomy labs, neuroanatomy blocks on vertebrobasilar circulation, and radiology teaching files when correlating posterior elements with CT bone windows. Spine surgeons and device teams will find it useful for presentations on C1-C2 fixation, safe zones around the vertebral artery, and preoperative planning discussions that reference posterior midline landmarks and the lateral mass corridor. Anatomical accuracy verified by SciePro's Medical Advisory Board.