Summary Rheumatoid cervical spondylitis is seen in patients with rheumatoid arthritis (RA) and comprises 3 specific patterns of cervical spine instability, including atlantoaxial subluxation, basilar invagination, and subaxial subluxation Diagnosis is made radiographically with cervical spine flexion-extension radiographs and MRI studies to measure the degree of spinal cord compression Treatment may involve observation or decompression with instrumentation depending on patient neurologic status, degree of mechanical instability, and severity of spinal cord compression EPIDEMIOLOGY Present in 90% of patients with RA diagnosis often missed ETIOLOGY Cervical rheumatoid spondylitis presents with 3 main patterns of instability atlantoaxial subluxation most common form of instability basilar invagination subaxial subluxation Classification Ranawat Classification Class I Pain, no neurologic deficit Class II Subjective weakness, hyperreflexia, and dysesthesias Class IIIA Objective weakness, long tract UMN signs Patient is ambulatory Class IIIB Objective weakness, long tract UMN signs Patient is non-ambulatory Do NOT operate Presentation Symptoms symptoms and physical exam findings are similar to cervical myelopathy neck pain neck stiffness occipital headaches due to irritation of the lesser occipital nerve (a branch of the C2 nerve root) gradual onset of weakness and loss of sensation Physical exam hyperreflexia upper and lower extremity weakness ataxia (gait instability and loss of hand dexterity) Imaging Radiographs flexion-extension x-rays always obtain before elective surgery CT scan useful to delineate bony anatomy and for surgical planning MRI study of choice to evaluate the degree of spinal cord compression and identify myelomalacia General Treatment Nonoperative pharmacologic therapy pharmacologic treatment for RA has seen significant recent advances, which has led to a decrease in surgical intervention Operative spinal decompression and stabilization indications goal is to prevent further neurologic progression; surgery may not reverse existing deficits Atlantoaxial Subluxation Introduction present in 50-80% of patients with RA most commonly involves anterior subluxation of C1 on C2 (though lateral and posterior displacement may also occur) Mechanism caused by pannus formation between the dens and ring of C1, leading to the destruction of the transverse ligament and dens Radiographs controlled flexion-extension views to determine AADI and SAC / PADI AADI (anterior atlanto-dens interval) instability is defined as >3.5 mm of motion between flexion and extension views instability alone is not an indication for surgery >7 mm of motion may indicate disruption of alar ligament >10 mm of motion is an indication for surgery because of increased risk of neurologic injury PADI / SAC (posterior atlanto-dens interval / space available for cord) <14 mm is an indication for surgery because of increased risk of neurologic injury >13 mm is the most important radiographic measurement for predicting complete neural recovery after decompressive surgery Treatment nonoperative indicated in stable atlantoaxial subluxation operative posterior C1-2 fusion general indications for surgery AADI >10 mm (even if no neurologic deficits) SAC / PADI <14 mm (even if no neurologic deficits) progressive myelopathy indications for posterior C1-2 fusion able to reduce C1 to C2 (no need to remove posterior arch of C1) technique transarticular screws eliminate the need for halo immobilization obtain preoperative CT to identify the location of the vertebral arteries occiput-C2 fusion ± resection of posterior C1 arch indications used when atlantoaxial subluxation is combined with basilar invagination resection of C1 posterior arch for complete decompression leads to indirect decompression of anterior cord compression caused by pannus formation may be required if atlantoaxial subluxation is not reducible odontoidectomy indications rarely indicated used as a secondary procedure when there is residual anterior cord compression (due to pannus formation) that fails to resolve following a posterior spinal fusion pannus often resolves following posterior fusion alone, due to a decrease in instability Basilar Invagination Introduction also known as superior migration of odontoid (SMO) tip of dens migrates above the foramen magnum present in 40% of RA patients often seen in combination with fixed atlantoaxial subluxation Mechanism cranial migration of the dens results from erosion and bone loss between the occiput, C1, and C2 Imaging radiographic lines Ranawat C1-C2 index center of C2 pedicle to a line connecting the anterior and posterior C1 arches normal measurement in men is 17 mm and in women is 15 mm distance of <13 mm is consistent with impaction most reproducible measurement McGregor's line line drawn from the posterior edge of the hard palate to the caudal posterior occiput curve cranial settling is present when the tip of dens is >4.5 mm above this line can be difficult to measure when the dens is eroded Chamberlain's line line from dorsal margin of hard palate → posterior edge of the foramen magnum abnormal if the tip of dens lies >5 mm proximal to Chamberlain's line normal distance from tip of dens to basion of occiput is 4-5 mm often hard to visualize on standard radiographs McRae's line defines the opening of the foramen magnum the tip of the dens may protrude slightly above this line, but impaction is not present if the dens is below this line MRI cervicomedullary angle <135° suggests impending neurologic impairment Treatment operative occiput-C2 fusion indications progressive cranial migration (>5 mm) neurologic compromise cervicomedullary angle <135° on MRI transoral or anterior retropharyngeal odontoid resection indications brainstem compromise Subaxial Subluxation Introduction present in 20% of patients with RA often occurs at multiple levels often combined with upper cervical spine instability lower spine involvement is more common with: steroid use males seropositive RA nodules present severe RA Pathophysiology pannus formation and soft-tissue instability of the facet and Luschka joints Radiographs subaxial subluxation (of vertebral body) of >4 mm or >20% indicates cord compression cervical height index (body height/width) <2.0 is almost 100% sensitive and specific for predicting neurologic compromise Treatment operative posterior fusion and wiring indications >4 mm / >20% subaxial subluxation with intractable pain and neurologic symptoms Operative Complications Failure to improve symptoms outcomes are less reliable in Ranawat grade IIIB (objectively weak with UMN signs and nonambulatory) Pseudarthrosis 10-20% rate decreases with extension of the construct to the occiput Adjacent level degeneration