Review Question - QID 214134

A cervicomedullary angle <135° is suggestive of impending neurologic deterioration with basilar invagination and is an indication for surgical decompression and stabilization.

Rheumatoid arthritis (RA) is a polyarticular inflammatory arthropathy that has characteristic pathology in the cervical spine. Most patients with cervical spine involvement develop atlantoaxial instability, which is characterized by anterior atlanto-dens interval >3.5 mm with neurologic complications associated with posterior atlanto-dens interval <14 mm. Basilar invagination is another manifestation and is characterized as the superior migration of the dens into the foramen magnum leading to compression of the medulla oblongata. This can be signified radiographically by the tip of the dens appearing proximal to McRae's line (opening of the foramen magnum), the tip of the dens appearing >4.5 mm superior to McGregor's line (line drawn from posterior edge of the hard palate to the inferior edge of the occiput), or a cervicomedullary angle <135°. A cervicomedullary angle <135° is suggestive of impending neurologic impairment and should be addressed with surgical decompression and stabilization.

Stein et al. performed a retrospective study of the National Inpatient Sample of cervical fusion procedures performed for rheumatoid arthritis and the general population. They reported that there has been a significant decrease in atlantoaxial fusion and posterior cervical fusion for rheumatoid arthritis but an overall increase in an anterior cervical fusion in the general population. They concluded that the use of disease-modifying antirheumatic drugs (DMARDs) has decreased the need for cervical fusion due to rheumatoid arthritis and an increase in the incidence of degenerative disc disease that typically affects the general population.

Kim and Hilibrand reviewed the evaluation and management of cervical spine manifestations of rheumatoid arthritis. The authors stated that surgical treatment is recommended in the presence of progressive neurologic deficits, chronic neck pain in the setting of radiographic instability, basilar invagination, posterior atlantoaxial interval ≤14 mm, sagittal canal diameter <14 mm, or cervicomedullary angle <135°. The authors concluded that despite a high incidence of surgical complications, properly performed surgery can lead to marked neurologic recovery.

Illustration A is a lateral cervical spine radiograph that demonstrates the measurement of space available for cord (posterior atlanto-dens interval) and anterior atlanto-dens interval. Illustration B is a lateral cervical spine radiograph that demonstrates McGregor's line and the evaluation for basilar invagination. Illustration C is a sagittal T2 MRI of the cervical spine with the measurement of the cervicomedullary angle.

Incorrect answers:
Answer 1: A posterior atlanto-dens interval <14 mm is considered a surgical indication due to critical spinal cord compression.
Answer 2: An anterior atlanto-dens interval >10 mm is considered a surgical indication due to impending neurologic impairment.
Answer 3: Basilar invagination is present when the tip of the odontoid process is 4.5 mm proximal to McGregor's line.
Answer 5: Subaxial sagittal canal diameter <14 mm is considered a surgical indication due to impending neurologic impairment.