Atlantoaxial Instability (AAI)

Etiology

Ankylosing Spondylitis (see Ankylosing Spondylitis)
Enteropathic Arthritis
Psoriatic Arthritis (see Psoriasis)
Reiter’s Syndrome (see Reiters Syndrome)
Rheumatoid Arthritis (RA) (see Rheumatoid Arthritis)
- Physiology: transverse ligament inflammation, predisposes atlantoaxial subluxation
Systemic Lupus Erythematosus (SLE) (see Systemic Lupus Erythematosus)

Cartilage-Hair Hyperplasia
Cerebral Palsy (see Cerebral Palsy)
Chondrodysplasia Punctata
Congenital Scoliosis
Corticosteroid Therapy (see Corticosteroids)
Down Syndrome (see Down Syndrome)
- Physiology: tranverse ligament laxity
Dwarfism (see xxxx)
Head and Neck Infection (Especially Pharyngeal Infection) (see Deep Neck Infection)
- Physiology: transverse ligament inflammation, predisposing to atlantoaxial subluxation
Hypoplasia or Absence of Dens
Kniest Syndrome
Larsen Syndrome
Metatropic Dysplasia
Morquio Syndrome
Mucopolysaccharidoses
Neurofibromatosis (see Neurofibromatosis)
Odontoid Abnormalities
Os Odontoideum
Ossiculum Terminale
Osteogenesis Imperfecta
Pseudoachondroplasia
Scott Syndrome
Spondyloepiphyseal Dysplasia Congenita
Third Condyle
Trauma to Neck
Tumors
- Physiology: may cause fracture of body of the axis

Bony Odontoid Abnormalities: may be due to either abnormal odontoid development/ossification or fracture
Fracture of Body of the Axis: may occur with tumors
Transverse Ligament Laxity/Inflammation: may occur with RA and infections

Increased Risk of Spinal Cord Injury (see Acute Spinal Cord Injury and Chronic Spinal Cord Injury)