C1 vertebra

The atlantoaxial joint is a pivot type of synovial joint located between the dens of the axis (C2 vertebra) and the anterior arch of the atlas (C1 vertebra), secured by ligaments, enabling rotational movement of the head. This joint plays a crucial role in allowing side-to-side head rotation, such as when shaking the head to say “no,” while maintaining stability in the upper cervical spine. This article explores the anatomical structure of the atlantoaxial joint, its physical functions, and its significance in neck mobility.

The CT scan image displays an axial view of the first cervical vertebra (C1), also known as the atlas, with a notable unfused posterior arch highlighted by the red arrow. This congenital anomaly represents a failure of proper fusion during embryonic development of the posterior neural arch components.