Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disorder that commonly affects the cervical spine. Three characteristic patterns of cervical instability result from rheumatoid involvement: atlantoaxial impaction (AAI), atlantoaxial subluxation (AAS), and subaxial subluxation (SAS). Treatment strategies include periodic assessment for clinical and radiographic progression, medical management, and early surgical intervention to prevent permanent neurologic injury.
Rheumatoid factor seropositivity
Greater initial C-reactive protein level
Advanced peripheral joint disease (specifically rapid loss of carpal height)
Predictors of Recovery
Degree of preoperative neurologic deficit associated with a strong predictor of postoperative neurologic status.
Any degree of AAI or cord compression on magnetic resonance imaging (MRI) is a significant risk for neurologic injury, and these conditions should be considered candidates for prophylactic decompression, stabilization, or both.
Posterior atlantodens interval less than 13 mm is associated with a greater rate of neurologic sequelae.
Less than 10 mm is associated with no neurologic recovery.
Most commonly accepted indications for surgical intervention include neurologic deterioration and intractable pain with spinal instability.
Surgery may also be warranted in situations without neurologic findings:
AAS with a posterior atlantodental interval less than or equal to 14 mm
AAI represented by odontoid migration more than 5 mm rostral to McGregor’s line
SAS with sagittal canal diameter less than or equal to 14 mm
Cervicomedullary angle less than 135 degrees
Use of preoperative halo traction has been recommended to reduce the degree of impaction and obviate the need for foramen magnum decompression or odontoid resection.
When traction is unsuccessful, symptomatic decompression with a transoral odontoid resection or C1 laminectomy, together with posterior stabilization, is required.
When AAS is reducible, a variety of posterior fusion techniques are available, with our preferred method of treatment being a C1-2 lateral screw technique.
When AAS is irreducible with symptomatic cord compression, a combination of posterior laminectomy and C1-2 fusion and stabilization should be considered.
Preoperative halo-vest immobilization can provide temporary stabilization and reduction of displacement, often with immediate improvement in neurologic deficits.
Reducible subluxations can be fused anteriorly or posteriorly.
Optimal treatment of irreducible subluxations is anterior decompression and fusion.
Excessive trauma caused by standard intubation has been associated with a 14% incidence rate of upper-airway obstruction after extubation. This rate can be reduced to 1% with fiberoptic assistance.
Skin lesions and corticosteroid use notably increase the rate of wound complications and infections.
Bone quality tends to be tenuous in the population, and aggressive instrumentation and meticulous arthrodesis techniques are essential to avoid catastrophic nonunions.
Rheumatoid arthritis (RA) is a chronic, inflammatory, autoimmune disorder characterized by polyarthritic disturbance of the peripheral joints and early involvement of the cervical spine. The frequency rate of cervical involvement ranges from 17% to 86%. The cause of the disease is unknown but is likely to be multifactorial with a relatively strong genetic component. Chronic synovial inflammation leads to progressive destruction of the joints, ligaments, and bone, particularly in the atlantoaxial region. Three characteristic patterns of instability resulting from rheumatoid involvement of the cervical spine may occur in isolation or in combination: atlantoaxial impaction (AAI), atlantoaxial subluxation (AAS), and subaxial subluxation (SAS). Each form of instability may lead to brainstem or spinal cord compression, or both, resulting in progressive neurologic deterioration and even death.
Rheumatoid involvement of the cervical spine is typically asymptomatic. Furthermore, radiographic evidence of instability does not correlate with neurologic deficits because 50% of patients manifest instability radiographically but not clinically. A careful physical examination is mandatory to reveal any subtle signs of neurologic involvement, which still occur in only 7% to 34% of patients. Occipital neuralgia, ear pain secondary to compression of the greater auricular branch of C2, facial pain as a result of trigeminal nucleus impingement, vertebrobasilar insufficiency, and myeloradiculopathy may be subtle neurologic findings.
Grading systems have been developed to assess disease severity, as well as treatment prognosis. The Ranawat grading system is widely utilized in clinical studies but has been criticized for lacking the ability to discriminate mild degrees of myelopathy ( Table 10-1 ). The Zeidman and Ducker modification of the Nurick myelopathy scale provides more differentiation with an assessment of gait and hand function ( Table 10-2 ). However, even this classification fails to account for severity of radiculopathic complaints, limiting its use in surgical decision making.
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The natural history of patients with RA with cervical involvement is one of variable progression. Fujiwara et al. have documented that over an average of 10.2-year follow-up of 161 patients, 57% of patients experienced development of radiographic evidence of subluxation. Other authors have quoted radiographic progression between 15% and 87%. Fortunately, clinical progression (10–57%) is less prevalent and does not appear to have a direct correlation with radiographic progression of disease. Risk factors for clinical progression include male sex, rheumatoid factor seropositivity, greater initial C-reactive protein levels, presence of subcutaneous nodules, advanced peripheral joint disease (specifically rapid loss of carpal height), and use of corticosteroids. Patients with any degree of AAI or cord compression on magnetic resonance imaging (MRI) are at significant risk for neurologic injury and should be considered strong candidates for prophylactic decompression or stabilization, or both.
Disease Pathology and Radiographic Evaluation
Plain radiography is an inexpensive and highly effective method of detecting instability and monitoring cervical rheumatoid disease progression. The most common subluxation in patients with rheumatism is AAS. AAS results from either an incompetent transverse ligament or from erosion of the dens and is accentuated in flexion. Subluxation may occur anteriorly in the majority of patients, laterally in 20%, and posteriorly in 10% ( Figs. 10-1 A, B ). AAS severity can be assessed by measuring the anterior atlantodental interval (AADI). The AADI is the distance from the anterior aspect of the dens to the posterior aspect of the anterior ring of C1 (see Fig. 10-1 A ). The reference value in adults is 3 mm, with a value greater than 5 mm indicative of instability. Notably, the posterior atlantodental interval (PADI) has been found to be a better predictor of neurologic injury because it reflects the potential space available for the spinal cord (except in situations of soft tissue canal expansion, i.e., rheumatoid pannus). The PADI is the distance between the posterior surface of the dens and the anterior edge of the posterior ring of C1 (see Fig. 10-1 A ). The critical lower limit is 13 mm, which has a 97% sensitivity to predict paralysis.
The second type of instability is AAI and is classically diagnosed on lateral radiographs. Several different radiographic findings indicate the presence of AAI. The Clark station method uses the position of the atlas in relation to the upper, middle, or lower third of the odontoid process in the midsagittal plane. If the anterior arch of the atlas is level with the middle third (station 2) or the caudal third (station 3) of the odontoid process, AAI is present. McRae’s line connects the anterior and the posterior margins of the foramen magnum. The tip of the odontoid should lie 1 cm below this line. Chamberlain’s line is drawn from the hard palate margin to the posterior margin of the foramen magnum. The odontoid tip should not project beyond 3 mm above this line. McGregor’s line connects the posterior margin of the hard palate to the most caudal point of the occiput ( Fig. 10-2 ). The odontoid should not project beyond 4.5 mm above that line. Because the odontoid may be difficult to see in presence of osteopenia or destruction, two other radiographic markers of AAI have been described. The Redlund-Johnell distance is measured as a perpendicular distance from the middle of the lower end plate of the axis to McGregor’s line (see Fig. 10-2 ). The normal distance is 34 mm in men and 29 mm in women. The Ranawat criterion is the distance between center of pedicle of axis and transverse axis of the atlas (see Fig. 10-2 ). A distance less than 15 mm in male and less than 13 mm in female patients indicates AAI. Despite many radiographic tools, no single screening test possesses a sensitivity greater than 90%; however, when the Clark, Redlund-Johnell, and Ranawat criteria were utilized and at least one of the tests is positive, the sensitivity increases to 94%, with negative predictive value of 91%. An MRI can also be utilized to diagnosis AAI. A cervicomedullary angle less than 135 degrees is indicative of AAI ( Fig. 10-3 ).
The radiographic appearance of the last instability pattern, SAS, is characteristic and includes not only sagittal plane listhesis of sequential vertebral bodies (below C2) but also posterior element changes, including facet joint erosions and widening. This deformity is caused by destabilization of the facet joints as a result of weakening of the capsule and interspinous ligaments. As with the other two deformities, plain radiographs are an essential part of the screening test. The classic radiographic finding is the “stepladder” spine indicative of multiple, sequential spondylolistheses. SAS may be differentiated from degenerative spondylolisthesis by its lack of osteophyte formation and involvement of C2-C3, C3-C4, or both ( Figs. 10-4 A-C ). Subluxation is usually anterior, occasionally lateral, and rarely in the posterior direction. A lateral flexion and extension radiograph should also be obtained to determine whether dynamic instability exists. The most important measurement on plain radiographs is determining the minimal spinal cord diameter behind the slipped vertebra. If the distance is less than 14 mm, possible cord compression exists. Because soft tissue pannus may compress the cord, a radiographic measurement of 13 mm could have as little as 8 to 12 mm available for the cord. Therefore, if neurologic symptoms are present or the PADI/subaxial canal diameter is less than 14 mm, MRI should be ordered.