Atlantoaxial subluxation

[Gregory]

Atlantoaxial subluxation is misalignment of the 1st and 2nd cervical vertebrae, which may occur only with neck flexion.
(See also Evaluation of Neck and Back Pain.)
Atlantoaxial subluxation can result from major trauma or can occur without trauma in patients with rheumatoid arthritis, juvenile idiopathic arthritis, or ankylosing spondylitis. This disorder is very rare.
Atlantoaxial subluxation is usually asymptomatic but may cause vague neck pain, occipital headache, or occasionally intermittent (and potentially fatal) cervical spinal cord compression.