Surgical Approaches to the Craniovertebral Junction in Rheumatoid Arthritis

Overview

Pathologic processes that may involve the craniovertebral junction (CVJ) include rheumatoid arthritis (RA), infection, trauma, tumor, Down syndrome and other congenital anomalies, osteoarthritis, osteogenesis imperfecta, achondroplasia, and iatrogenic instability.

RA is a chronic, progressive, systemic inflammatory disease that peaks in the fourth through sixth decades and leads to inflammation of the synovial joints and surrounding tissue, usually in a symmetric fashion. The cervical spine and CVJ are the most affected parts of the spinal column; synovial and facet involvement is present in up to 90% of RA patients ( Fig. 9-1 ). Cervical spine disease manifests as facet inflammation, synovitis, loss of cartilage, ligamentous laxity, and bony erosion; all lead to cervical instability.

The etiology of RA is unknown but has been associated with the class II human leukocyte antigen, HLA-DR4. Spinal instability is the direct result of rheumatoid bone, cartilage, and ligament destruction. This causes synovial inflammation and instability by atlantoaxial subluxation (AAS) as a result of transverse ligament failure and granulation formation between the C1–C2 lateral masses; this causes anteroposterior (AP) and rotatory subluxation or fixation ( Fig. 9-2 ). Cranial settling or basilar invagination is also frequently seen because of bony erosion of the occipital condyles and lateral masses that causes vertical penetration of the odontoid process into the foramen magnum. As a result, this instability causes the dens to move superiorly and posteriorly, compressing the brainstem ( Fig. 9-3 ). Additionally, C1–C2 instability from synovitis causes fibroblasts to proliferate, and granulation tissue forms a periodontoid pannus, which can become large enough to compress the cervicomedullary junction ( Fig. 9-4 ).

Diagnosis and Evaluation

The goals of surgical treatment should be to treat pathology at the CVJ, including instability and neurologic compromise. The most common symptom in RA patients with cervical spine disease is pain in the upper cervical area with radiation to the mastoid or cranial regions. C2 nerve root compression from AAS may cause radicular pain and numbness in the distribution of the greater occipital nerve. Limb paresthesias, hand clumsiness, urinary incontinence or retention, diplopia, vertigo, head tilt, basilar migraine, nystagmus (usually downbeat and lateral gaze), tinnitus, and involuntary leg spasms may also be present. Neurologic compromise typically results in pain, myelopathy, or lower cranial nerve deficits. Meticulous physical exam is necessary to detect hyperreflexia, spasticity, and pathologic reflexes; early diagnosis is crucial. The symptomatology, extent of involvement, and radiographic findings must be considered before conservative or surgical intervention is proposed. Once cervical myelopathy has been established, the natural history without surgical intervention is grave, and mortality is high. Up to half of the patients with cord compression will die within a year if left untreated. Goals of surgery must be discussed with the patient and family.

Atlantoaxial instability is easily demonstrated on plain film radiography; therefore initial radiographic evaluation begins with plain, multiview radiographs to establish landmarks and lateral-bending, open-mouth, oblique, flexion, and extension films. Subluxation, odontoid erosion, cranial settling, and C1–C2 instability can all be reliably detected with x-rays, which are then supplemented with thin-section multiplanar computed tomography (CT), magnetic resonance imaging (MRI) or MR angiography (MRA), and CT myelograms as needed ( Figs. 9-5 and 9-6 ).

Atlantoaxial Subluxation

This is the most common type of cervical subluxation and accounts for up to 65% of subluxation in RA patients. Anterior subluxation makes up the majority of these cases, whereas lateral and posterior subluxation may occur less frequently. AAS is caused by erosive synovitis in the occipital–cervical (O–C1) and C1–C2 joints and in the odontoid process and by laxity in the transverse ligament. For stability the C1–C2 complex depends on the transverse and alar ligaments and, to a lesser degree, the apical ligaments. Anterior AAS may result in compression of the cervical cord, especially during flexion, as C1 slides forward onto C2 ( Fig. 9-7 ).

Cervicomedullary compression, as well as vertebral artery occlusion, may produce the clinical manifestation of AAS ( Figs. 9-8 and 9-9 ). Pain is the most frequent complaint, usually in the upper neck, radiating to the occiput or the vertex, and it is increased with flexion and rotation. On plain films, the anterior and posterior atlantodental interval should be measured to determine the amount of subluxation. The upper limit of normal is 3 mm in adults and 4 mm in children.

The most common procedure for stabilization of AAS is a posterior arthrodesis, which can be accomplished by several techniques, such as posterior screw fixation ( Fig. 9-10 ). Given the inherent instability of the rheumatoid process, however, close follow-up must ensue to investigate whether cranial settling of the C1–C2 mass occurs postoperatively ( Fig. 9-11 ).

Atlantoaxial Rotatory Subluxation

Up to 20% of RA patients may have atlantoaxial rotary subluxation (AARS). The pathologic process for rotatory subluxation is the same as in AAS, allowing for rotation at the O–C1–C2 joints ( Fig. 9-12 ). This may result in significant pain and ultimately in fixed torticollis ( Figs. 9-13 and 9-14 ). Cervical and occipital pain are the most common clinical symptoms, and C2 dermatomal hyperalgesia may also be present. The diagnosis is confirmed radiographically: more than 2 mm of subluxation of the C1 lateral masses onto C2 has been established as the definition. Asymmetry of the lateral masses on open-mouth plain film radiographs is also suggestive of rotation.

If rotation is not fixed, low-weight halo–ring traction over a period of 3 to 10 days may be placed to correct the deformity, and then an O–C2 fusion may be performed for definitive reduction. To prevent cranial settling, patients may also be kept in a halo–vest orthosis for 10 to 12 weeks postoperatively.

Indications and Relative Contraindications

The decision to intervene surgically is complex. A clear understanding of the patient’s overall health, symptoms, and neurologic findings on exam is crucial. Indications for surgery include 1) impending or established neurologic injury to the spinal cord or brainstem; 2) reduction, stabilization, and/or decompression of the instability; 3) AAS; 4) correction of a deformity in AARS; 5) fixed CVJ kyphosis; and 6) alleviation of intractable pain. No clear guidelines exist for operative intervention in patients with asymptomatic C1–C2 instability, and each case should be individually assessed.

Relative contraindications include severe osteopenia, because this may be difficult to stabilize postoperatively and may require halo traction; severe myelopathy or paralysis, when neurology may be irreversible; and when the patient is nonambulatory or is unlikely to regain ambulatory status (Ranawat III B). Far-lateral pathologies should be addressed by a different approach; this is covered in other chapters.

Surgical Approach

Multiple surgical approaches to the CVJ exist. In modern times, better knowledge of the biomechanics and the wide use of new instrumentation devices and endoscopy allow us to access the CVJ through multiple routes. Historically, several factors have been discussed that influence the treatment of CVJ abnormalities. These include 1) the reducibility of the lesion; that is, whether anatomic alignment must be restored to alleviate compression; 2) the direction and the mechanics of the compression; 3) the etiology of the compression and associated lesions; and 4) the presence of abnormal ossification centers.

The approach to the lesion or deformity is dictated by the location and nature of the compression. In select cases, stand-alone rigid posterior fixation is adequate for treating spinal compression attributable solely to AAS or cranial settling that may be reduced with traction( Figs. 9-15 and 9-16 ). In addition, when preoperative dynamic images support that the CVJ compression is reducible, and a periodontoid pannus does not cause significant neural compression, rigid posterior fixation of C1–C2 usually allows involution of the pannus, and direct surgical removal is unnecessary ( Figs. 9-17 through 9-19 ).