Cervical spine involvement occurs in about 90% of patients with rheumatoid arthritis. All rheumatoid arthritis patients should have a cervical spine examination. The physician should begin with getting cervical spine x-rays because this helps to diagnose atlantoaxial instability. Early aggressive medical treatment can decrease this risk. C1-C2 instability is common and can occur in up to 80% of cases. C1-C2 instability occurs due to transverse ligament pathology. Flexion/extension views will be beneficial for patients with rheumatoid arthritis, especially preoperative x-rays. If it looks bad, stabilize the spine before performing total hip or total knee procedures. Discover the C1-C2 instability and fix it first before doing elective total hip procedure. The normal A.D.I. in adults is less than 3mm. A.D.I. more than 3.5 mm indicates instability of the upper cervical spine may be present. A.D.I. more than 7mm indicates disruption of the alar ligament and these patients can have cervical spine myelopathy. The Atlanto-Dental Interval (A.D.I.) is an unreliable predictor of paralysis. The posterior atlanto-dental interval is a better screening test that can predict spinal cord injury. If the Posterior Atlanto-Dental Intreval (P.A.D.I.) is less than 14mm, this can predict a spinal cord injury. An MRI should be obtained. Surgery is performed if the A.D.I. is more than 10mm or if the P.A.D.I. is less than 14mm. Surgery is done by C1-C2 fusion.
Clinically, the C1-C2 instability could give neck pain, headache, and myelopathy with abnormal gait, paresthesia, and difficulty in fine motor control. Basilar Invagination occurs in about 40% of patients with rheumatoid arthritis. Basilar impression (invagination) occurs if the odontoid process tip is 5mm or more above Chamberlain’s line. In this case, do occiput to C2 fusion, plus or minus odontoid resection. Subaxial subluxation occurs in about 20% of patients and the indication for surgery is neurological compromise. If the space available for the spinal cord is less than 14mm, then do surgery (posterior fusion). Surgery is usually not successful with severe types of neurologic impairment.
Surgery should be performed if the patient has severe pain, neurological deficit, and x-rays showing that the P.A.D.I. is less than 14mm. Surgery should also be performed in cases of superior odontoid migration and subaxial subluxation with the sagittal canal diameter being less than 14mm. If the posterior atlanto-dental interval is more than 14mm, the patient will demonstrate significant motor recovery after surgery.