Spontaneous subluxation of the first and second cervical vertebrae, in rheumatoid arthritis, treated with spinal fusion

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SPONTANEOUS dislocation of the atlas on the axis has been known as an entity for some time, the first case reported is thought to be that of Bell in 1830.1 Since then there have been numerous published reports of atlantoaxial subluxation, most recently in relation to rheumatoid arthritis.2–17

The atlantoaxial joint has two axes of motion; the transverse axis which passes approximately through the center of the annulus osteofibrosus and permits flexion and extension of about 10 degrees; and the vertical axis, which also passes through the center of the annulus osteofibrosus and allows rotation of about 47 degrees. The tectorial membrane limits flexion and extension, and the alar ligaments limit rotation. The annulus osteofibrosus is composed of the transverse ligament and the anterior arch of the atlas which encircles the odontoid process and prevents anteroposterior motion of it in relation to the atlas.

Pathogenesis and incidence

Rheumatoid arthritis affects the bursae located on either side of the odontoid process and also the joints of Luschka. The odontoid process itself can become eroded by the disease and the transverse ligament can then become secondarily loosened.

The transverse ligament must be weakened or destroyed in order for the odontoid process to be subluxated in relation to the axis.18 Apparently the only way that the odontoid process is consistently dislocated by trauma is by gallows hanging, with the knot placed in a submental position.19

Sharp and Purser17 in a population study reported an incidence of 64.1 subluxations per thousand patients with . . .



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