Anterior Atlantoaxial Membrane

membrana atlantoaxialis anterior

The anterior atlantoaxial membrane is a broad, dense fibrous sheet connecting the inferior border of the anterior arch of the atlas to the anterior surface of the body of the axis. It represents the continuation of the anterior longitudinal ligament at the C1-C2 level and is reinforced centrally by the anterior atlantoaxial ligament, a rounded cord corresponding to the anterior longitudinal ligament proper.

Region: Neck

Biomechanics

Function & Actions

Limits extension at the atlantoaxial joint, reinforces the anterior C1-C2 joint capsule, and together with the posterior atlantoaxial membrane provides anterior and posterior soft tissue boundaries of the C1-C2 articulation.

Clinical Relevance

Clinical Notes

The anterior atlantoaxial membrane is assessed as part of craniocervical instability workup in rheumatoid arthritis and ankylosing spondylitis, where inflammatory erosion of the C1-C2 joints and anterior membrane contributes to atlantoaxial instability. Rupture of this membrane occurs in high-energy atlantoaxial rotatory subluxation. The anterior membrane and ligament are relevant landmarks in anterior surgical approaches to the upper cervical spine.

Pathology

Common Injuries & Conditions

Atlantoaxial Instability in Rheumatoid Arthritis

Synovial inflammatory erosion of the atlantoaxial joints and anterior atlantoaxial membrane allows anterior subluxation of C1 on C2, visible as an increased atlanto-dens interval greater than 3 mm on lateral flexion radiograph, potentially compressing the spinal cord and requiring posterior C1-C2 fusion.