The transverse ligament of the atlas is the primary stabiliser of the atlantoaxial joint, holding the odontoid process firmly against the posterior surface of the anterior arch of the atlas and preventing forward displacement of C1 on C2. Its failure, from trauma or rheumatoid arthritis destruction, allows the odontoid process to migrate posteriorly into the spinal cord, a potentially fatal complication.
| Origin | Medial surface of the lateral mass of C1 (atlas) |
|---|---|
| Insertion | Medial surface of the opposite lateral mass of C1 |
| Actions | Holds the odontoid process of the axis against the anterior arch of the atlas, preventing forward subluxation of C1 on C2 |
|---|
Transverse ligament rupture from a high-energy axial load or flexion injury produces atlantoaxial instability that may compress the spinal cord. The space available for the spinal cord measured on lateral radiographs or CT, the Steel rule of thirds (one third dens, one third cord, one third space), determines the risk of cord injury. Rheumatoid arthritis causes transverse ligament destruction through chronic inflammation and is a leading cause of atlantoaxial instability requiring C1-C2 fusion.
Disruption from trauma or rheumatoid arthritis producing atlantoaxial instability with risk of odontoid compression of the spinal cord, requiring posterior C1-C2 fusion when instability is demonstrated on dynamic radiographs.
