Explanation:
The transverse ligament of the atlas is the most important stabilizing structure of the atlantoaxial joint. It holds the dens of the axis against the anterior arch of the atlas and prevents anterior displacement of the atlas relative to the axis. Disruption of this ligament can lead to atlantoaxial instability and potential spinal cord compression. Conditions such as rheumatoid arthritis, trauma, and congenital anomalies may compromise this ligament. Radiologically, the atlantodens interval increases when the ligament is incompetent, particularly during flexion radiographs. Reference: Fielding JW et al., 'Atlanto-axial rotatory fixation', Journal of Bone and Joint Surgery (1977).