AKA atlantoaxial impaction. Erosive changes in the lateral masses of C1 → telescoping of the atlas onto the body of C2 causing ventral migration of C1 with resultant ↓ in AP diameter of the spinal canal. There is concomitant upward displacement of the dens. The posterior arch of C1 often protrudes superiorly through the foramen magnum. All of these factors lead to compression of the pons and medulla. Rheumatoid granulation tissue behind the odontoid also contributes to the brainstem compression. Vertebral artery and/or anterior spinal artery compression may also cause neurologic dysfunction.
The degree of erosion of C1 correlates with the extent of odontoid invagination.
Pain may occur as a result of compression of the C1 and/or C2 nerve roots. Compression of the medulla can cause cranial nerve dysfunction. Motor exam usually difficult because of severe polyarticular degeneration and associated pain. Sensory findings (all non-localizing): diminished vibratory, position, and light touch.
Between 1978 and 1984, Menezes et al., treated 45 rheumatoid arthritis patients who were symptomatic with “cranial settling.” This consisted of vertical odontoid penetration through the foramen magnum (9 to 33 mm), occipito-atlanto-axial dislocation, lateral atlantal mass erosion, downward telescoping of the anterior arch of C-1 on the axis, and rostral rotation of the posterior arch of C-1 producing ventral and dorsal cervicomedullary junction compromise. Cervicomedullary junction dysfunction has mistakenly been called “entrapment neuropathy,” “progression of disease,” or “vasculitis.” Occipital pain occurred in all 45 patients, myelopathy in 36, blackout spells in 24, brain-stem signs in 17, and lower cranial nerve palsies in 10. Four patients had prior tracheostomies. Four previously asymptomatic patients with “cranial settling” presented acutely quadriplegic. The factors governing treatment were reducibility and direction of encroachment determined by skeletal traction and myelotomography. Transoral odontoidectomy was performed in seven patients with irreducible pathology. All patients underwent occipitocervical bone fusion (with C-1 decompression if needed) and acrylic fixation. Improvement occurred during traction, implying that compression might be the etiology for the neurological signs. There were no complications. Thus, “cranial settling” is a frequent complication of rheumatoid arthritis; although it is poorly recognized, it has serious implications and is treatable 1).
May attempt with Gardner-Wells tongs. Begin with ≈ 7 lbs, and slowly increase up to 15 lbs. Some may require several weeks of traction to reduce.
Reducible cases: posterior occipitocervical fusion ± C1 decompressive laminectomy. Irreducible cases: requires transoral resection of odontoid. May perform before posterior fusion (but then must be kept in traction while waiting for posterior fusion).