Magnetic resonance imaging in the evaluation of patients with rheumatoid arthritis and subluxations of the cervical spine. 
We used magnetic resonance imaging (MRI) to examine 21 patients with rheumatoid arthritis and vertebral subluxations of the cervical spine, in whom neurologic symptoms and signs indicated spinal cord compression.  Based on neurologic signs, the patients were assigned to 1 of 3 classes: class I, no objective signs of cervical myelopathy (9 patients); class II, only 1 objective sign of cervical myelopathy (4 patients); or class III, 2 or more objective signs of cervical myelopathy (8 patients).  Atlantoaxial subluxation (20 patients) and subluxations below C2 (6 patients) were detected equally well by MRI and radiography.  MRI revealed physical distortion of the spinal cord in all class III patients with compressive myelopathy.  This distortion was found less frequently in class II and class I patients (3 patients), and the difference was statistically significant (P less than 0.005, class III versus class I and class II).  No correlation was found between the vertebral dislocation (measured in millimeters) on plain radiographs and the presence of cord distortion on MRI.  Myelography in class III patients showed that passage of contrast medium was blocked at the same level as the cord distortion seen on MRI.  These findings suggest that MRI can serve as a useful, noninvasive procedure in the diagnosis and management of rheumatoid arthritis patients in whom compressive cervical myelopathy is suspected.