How is the cervical spine involved in Rheumatoid Arthritis?
Historically, the cervical spine is involved in 30% to 50% of RA patients, with C1–C2 the most commonly involved level. Fortunately, the rates of significant cervical spinal disease in RA are decreasing with modern therapy. Arthritic involvement of the cervical spine can lead to instability with potential impingement of the spinal cord; thus it is important for the clinician to obtain radiographs of the cervical spine before surgical procedures requiring intubation. It is important to note that cervical spine disease often parallels peripheral joint disease. The earliest and most frequent symptom of subluxation is pain radiating to the occiput. Pain, neurologic involvement, and death are the main concerns with subluxation. The patterns of cervical spine involvement include:
- • C1–C2 subluxation (60%–65% cases) can result in anterior (most common), lateral (rotary), and posterior (least common) atlantoaxial subluxation. Anterior subluxation at C1–C2 results in a widening of the gap between the arch of C1 and the odontoid of C2 (>3 mm). This is caused by synovial proliferation around the articulation of the odontoid process with the anterior arch of C1, leading to stretching and rupture of the transverse and alar ligaments, which keep the odontoid in contact with the arch of C1. The risk of spinal cord compression is greatest when the anterior atlantoodontoid interval is ≥9 mm, or the posterior atlantoodontoid interval is ≤14 mm.
- • C1–C2 impaction (20%–25% cases; sometimes referred to as superior migration of the odontoid) is the next most common form of cervical spine disease in RA. Destruction is between the occipitoatlantal and atlantoaxial joint articulations between C1 and C2, causing a cephalad movement of the odontoid into the foramen magnum, which may impinge on the brainstem. Overall, it has the worst prognosis neurologically, especially when the odontoid is ≥5 mm above Ranawat’s line.
- • Subaxial involvement (10%–15% cases) is the least common and typically involves C2–C3 and C3–C4 facets and intervertebral disks. This can lead to “stair-stepping” with one vertebrae subluxing forward on the lower vertebrae. Translation of more than 3.5 mm of one vertebra on the other is usually clinically relevant. Subaxial disease usually occurs later than other forms of cervical involvement