Wednesday, December 12, 2018

Brain & Spine Disorders

Occipitocervical Instability


Occipitocervical dislocation (dislocation of the head from the neck) injuries are relatively rare and account for approximately 1% of all injuries involving the cervical spine. However, these injuries are often severe and, therefore, tend to be fatal. In fact, they are thought to be underdiagnosed. Multiple ligaments are responsible for structural support at the occipitocervical junction.  The extent of damage to these ligaments determines the type of fixation (usually surgical) that is required.

There are a variety of ways to determine instability at the occipitoatlantal or atlantoaxial joints. Plain radiography (X-rays) is usually the first-line imaging modality. Findings related to occipitoatlantal translation, lateral atlas displacement, or atlantoaxial translation can raise suspicions of instability. Computed tomography (CT) improves definition of these articulations and can also detect rotational subluxation. Magnetic resonance imaging (MRI) can help determine ligamentous injury, especially of the transverse atlantal ligament. However, it should be used with caution as the sole modality for determining stability because it is highly sensitive to any type of soft tissue injury.

Other causes of occipitocervical instability include rheumatoid disease and severe degenerative neck diease.  Instability may also occur following surgery of the upper cerical spine (generally for a tumor). 

The evolution of occipitocervical fixation with advancing technology and progressive construct stability has allowed treatment of more complex craniocervical instabilities with a higher success rate and less cumbersome postoperative immobilization. Initial on-lay fusion and simple wire techniques required periods of traction followed by a halo. Rod and wire constructs were more stable, but continued to have difficulty preventing axial loads due to the rods pistoning through the sublaminar wires. Plate and screw constructs were the first truly stable types of occipitocervical fixation, but depended upon fixed hole-hole distances in the plate, which made proper insertion of the screws sometimes difficult. Also, these devices do not have a rigid connection of the screw to the plate. Modern screw-rod devices allow independent insertion of the screw anchors as well as stable connection to the longitudinal rod.

Surgical Indications

The most common causes of occipitocervical instability are rheumatoid arthritis with vertical migration of the odontoid and trauma to the ligamentous structures of the craniocervical junction. Tumors and infections may also cause destruction of the stabilizing elements.

Neck Pain (Overview)
Neck Pain & Disorders (Cervical Spine)

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