The cervical spine often becomes involved early in the course of rheumatoid 
arthritis, leading to three different patterns of instability: atlantoaxial 
subluxation, atlantoaxial impaction, and subaxial subluxation. Although 
radiographic changes are common, the prevalence of neurologic injury is 
relatively low. The primary goal of treatment is to prevent permanent neurologic 
injury while avoiding potentially dangerous and unnecessary surgery. Strategies 
include patient education, lifestyle modification, regular radiographic 
follow-up, and early surgical intervention, when indicated. Magnetic resonance 
imaging is indicated when neurologic deficit (myelopathy) occurs or when plain 
radiographs show atlantoaxial subluxation with a posterior atlantodental 
interval < or =14 mm, any degree of atlantoaxial impaction, or subaxial stenosis 
with a canal diameter < or =14 mm. Surgery should be considered promptly for any 
of the following: progressive neurologic deficit, chronic neck pain in the 
setting of radiographic instability that does not respond to nonnarcotic pain 
medication, any degree of atlantoaxial impaction or cord stenosis, a posterior 
atlantodental interval < or =14 mm, atlantoaxial impaction represented by 
odontoid migration > or =5 mm rostral to McGregor's line, sagittal canal 
diameter <14 mm, or a cervicomedullary angle <135 degrees.