Condition Overview
Atlantoaxial Dislocation (AAD), or C1-C2 instability, involves the loss of stability between the first and second vertebrae. Unlike lower spinal joints, the C1-C2 complex relies heavily on ligaments rather than bony interlocking, making it susceptible to severe displacement.
Instability allows the odontoid process (a peg-like projection of C2) to shift, which can compress the brainstem and upper spinal cord, leading to myelopathy or life-threatening respiratory failure.
Causes & Symptoms
Etiology
Linked to Down syndrome, Morquio syndrome, or os odontoideum (malformed C2 bone).
Trauma (accidents/falls) or inflammatory diseases like Rheumatoid Arthritis.
Clinical Presentation
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Severe Pain: Localized neck pain and suboccipital headaches.
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Sensory Issues: Vertigo, tinnitus, and numbness in the extremities.
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Motor Deficits: Progressive weakness, "electric shock" sensations (Lhermitte's sign), and myelopathy.
Diagnosis & Imaging
Confirmed diagnosis requires specialized imaging to assess both bone stability and soft tissue compression:
- CT Scans: The gold standard for defining bony anatomy and identifying fractures or congenital malformations.
- MRI: Essential for evaluating spinal cord compression, signal changes (myelomalacia), and ligamentous integrity.
- Dynamic X-rays: Flexion and extension views are used to measure the atlantodental interval (ADI) to confirm active instability.
Surgical Intervention
Surgery is indicated when instability causes neurological symptoms or poses a high risk of cord injury.
The treatment of choice. Screws are placed in the C1 lateral mass and C2 pedicle/pars, providing immediate rigid stability and high fusion rates.
Necessary if the instability extends to the junction between the skull (occiput) and the cervical spine.
In rare, irreducible cases, the odontoid process may be removed through the mouth to relieve direct compression on the cord.
Recovery & Prognosis
Fusion of C1-C2 typically results in a 50% reduction in neck rotation, as this joint is responsible for most of the "no" movement.
Modern posterior fusion techniques have excellent success rates in stabilizing the spine and preventing further neurological decline.
Potential complications include injury to the vertebral artery, infection, hardware failure, or non-union (failure of the bones to fuse).
