Interarticularis Of The Vertebral Arch Of Axis, Posterior View

Description

Pars interarticularis of the axis (C2) occupies the narrow bony bridge between the superior and inferior articular processes, positioned posterolateral to the vertebral canal and continuous medially with the lamina. In this posterior view, the junction between lamina and articular pillar is emphasized, with the base of the bifid spinous process lying in the midline and the paired laminae converging toward it. The superior articular facets sit superiorly and slightly laterally, while the inferior articular facets lie inferiorly, forming the zygapophysial joints with C1 and C3 respectively. Cortical margins are sharply defined. It is a small target. Clinically, C2 pars anatomy matters because traumatic defects here underlie the classic “hangman’s fracture” (traumatic spondylolisthesis of the axis) in which bilateral fractures through the pars interarticularis separate the anterior C2 body from the posterior elements. This fixed posterior perspective supports teaching and preoperative planning by making the pars-to-lamina relationship easy to track, the nearby articular pillars obvious, and the limited osseous stock apparent for posterior fixation strategies such as C2 pars screws or alternative trajectories when the pedicle is unfavorable. Instructors can also pair this view with CT teaching to explain why pars fractures may be subtle on plain radiographs but conspicuous on posterior element assessment. Neuroanatomy and musculoskeletal anatomy courses can use the illustration to anchor the terminology of vertebral arch components (lamina, articular processes, and pars interarticularis) without distraction from surrounding soft tissues. Spine surgery and radiology publications can cite it when discussing classification and management of C2 posterior element fractures, screw placement corridors, and the distinction between pars defects and more lateral pedicle injuries. Anatomical accuracy verified by SciePro's Medical Advisory Board.