Atlantoaxial widening of the right side of the atlantoaxial joint may be caused by atlantoaxial subluxation and ligamentous laxity. 1. Atlantoaxial subluxation: Atlantoaxial joint is the joint with the largest range of motion among the joints of the spine, and it is also a relatively unstable joint. Under external force, bone or ligament tears or ruptures may occur, and the distance between joints may become larger. As a result, imaging may reveal a widening of the right side of the atlantoaxial joint. 2. Ligamentous laxity: Most commonly seen in middle-aged and elderly people, the ligaments between the atlantoaxial joints become lax due to physiologic aging, which can also lead to a widening of the right side of the atlantoaxial joint. In addition to the above reasons, atlantoaxial joint occupying lesions such as tuberculosis, tumor, etc. can also lead to the above changes. It is recommended to go to the hospital for a complete examination to determine the cause of the disease and then give targeted treatment.