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Median atlantoaxial joint

The median atlantoaxial joint is a pivot synovial joint located between the dens (odontoid process) of the axis (C2) and the anterior arch of the atlas (C1). It consists of two articulations: one between the anterior surface of the dens and the posterior surface of the anterior arch of C1, and the posterior dens joint with the transverse ligament of the atlas, which stabilizes rotational movement. This joint allows axial rotation of the head, enabling side-to-side “no” movements. The median atlantoaxial joint is reinforced by the transverse, alar, and apical ligaments, and its integrity is crucial for maintaining stability of the craniocervical junction.

Synonyms

  • Atlanto-dens joint

  • Odontoid joint

  • Median C1-C2 joint

  • Pivot joint of the atlas and axis

Function

  • Facilitates axial rotation of the head and neck

  • Provides stability to the craniovertebral junction

  • Distributes forces between C1 and C2 during motion

  • Maintains alignment of the odontoid process with the anterior arch of the atlas

MRI Appearance
T1-weighted images:

  • The median atlantoaxial joint appears as a thin linear hypointense space between the dens (odontoid process) and the anterior arch of C1

  • Surrounding ligaments, including the transverse ligament, appear low signal intensity, providing contrast against the bone marrow of C1 and C2

  • Pathological changes, such as inflammatory arthritis or pannus formation, may appear as intermediate to hyperintense tissue with or without contrast enhancement

T2-weighted images:

  • The joint space remains hypointense, while synovial fluid, edema, or inflammatory tissue appears hyperintense, highlighting pathology

  • Useful for evaluating ligamentous injury, synovitis, or pannus formation in rheumatoid arthritis

STIR (Short Tau Inversion Recovery):

  • Fat suppression enhances edema or inflammatory changes

  • Normal joint and ligaments remain low signal, while abnormal fluid collections, edema, or pannus appear bright hyperintense

CT Appearance

  • The median atlantoaxial joint appears as a narrow space between the anterior arch of C1 and the dens of C2, often seen as a well-corticated articulation

  • The dens, anterior arch, and transverse ligament insertion sites are clearly visualized

  • Surrounding air (pharyngeal space) provides natural hypodense contrast, delineating the joint margins

  • CT is ideal for detecting fractures of the dens, anterior arch, or subluxation, as well as osseous erosions from inflammatory or degenerative disease

MRI images

Median atlantoaxial joint axial

MRI images

Median atlantoaxial joint