Atlantoaxial instability

Atlantoaxial instability (AAI) is characterized by excessive movement at the junction between the atlas (C1) and axis (C2) as a result of either a bone or ligament abnormality.

It can be caused by congenital conditions, inflammatory conditions like rheumatoid arthritis, as a result of physical trauma, or infection. It has been associated with Down’s Syndrome, Morquio's syndrome, Marfan syndrome, and Ehlers-Danlos syndrome.

It often co-occurs with craniocervical instability (CCI).

In individuals without predisposing conditions, it is thought to be extremely rare.

Symptoms

 * Neck pain
 * Neck stiffness, torticollis
 * Spasticity
 * Radius are symptoms
 * Lack of coordination
 * Clumsiness
 * Gait changes, difficulty with gait
 * Sensory deficits
 * Neurogenic bladder
 * Spasticity, clonus, hyperreflexia
 * Paraplegia, quadriplegia
 * Muscle weakness
 * Decreased hand dexterity
 * Blurred vision
 * Occipital headache

Rheumatoid arthritis
Chronic inflammation can cause laxity and stretching of the transverse ligament, the formation of a pannus, as well as bone erosion.

Grisel’s syndrome
Grisel’s syndrome occurs following inflammation of the soft tissue as a consequence of surgery or infection, frequently an upper respiratory infection. It is primarily seen in patients ages 5-12 but can also be seen in adults. It usually presents with torticollis, neck pain, neck tilt, and stiffness. It can often be treated with conservative therapies such as physical therapy, traction, immobilization, antiinflammatories and treatment of any underlying infection.

Co-morbid conditions
AAI can cause vertebrobasilar insufficiency.

Diagnosis
AAI is defined as an atlantodental (or atlantodens or atlas-dens) interval (ADI) of greater than 3 mm in adults and of greater than 5 mm in children as measured on plain radiography. The ADI is the distance between the odontoid process and the posterior border of the anterior arch of the atlas.