Inflammatory Arthritides

Jason C. Eck

Scott D. Hodges

While the majority of arthritic conditions of the spine are the result of degenerative arthritis, there are other types that can occur less frequently. The most common of these is the family of disorders referred to as the inflammatory arthritides. This collection of disorders includes rheumatoid arthritis (RA) and the seronegative spondyloarthropathies. The seronegative spondyloarthropathies include ankylosing spondylitis (AS), which is described in Chapter 25, diffuse idiopathic skeletal hyperostosis (DISH), reactive arthritis, psoriatic arthritis, and enteropathic arthritis.

Patients with inflammatory arthritis pose a unique challenge in diagnosis and management and must be properly distinguished from conventional degenerative disease in order to facilitate successful management. Failure to do so can lead to poor results and significant complications. This chapter provides a review of the characteristics of the various inflammatory arthritides including discussions on relevant anatomy, pathogenesis, epidemiology, classification, diagnosis, and treatment.

Rheumatoid Arthritis

Relevant Anatomy

RA is a chronic inflammatory disorder that affects the synovial lining of joints and leads to widespread destruction of the joints, deformity, and instability. The most common locations for involvement are the hands, the feet, and the cervical spine. Fortunately, due to substantial advancements in the pharmacologic management of RA, spinal involvement has become much less frequent and less severe over the last two decades.

Involvement of the spine is most frequently encountered in the upper cervical region, including the synovial joints of the atlanto-occipital, atlantoaxial, zygapophyseal, and uncovertebral joints. It can also affect the intervertebral disks and the bursal and ligamentous structures. The most common site of involvement is the atlantoaxial joint, where it can lead to subluxation and instability. Involvement of the transverse ligament can lead to ligamentous laxity, atlantoaxial instability, and anterior subluxation.

Instability at the atlantoaxial joint can lead to the formation of a pannus posterior to the odontoid process that may result in spinal cord compression. Posterior subluxation is less common and can be caused by erosion or fracture of the odontoid process. Superior subluxation is also possible with involvement of the atlantoaxial joints around the foramen magnum. Finally, lateral subluxation can be caused by erosion of the lateral masses and the odontoid process.

After the atlantoaxial joint, the next most common site of RA involvement in the spine is the subaxial cervical region. Erosion of the zygapophyseal joints and bursal structures can lead to kyphosis and subluxation of the subaxial cervical motion segments. Anterior subluxation of greater than 3.5 mm is considered indicative of instability. This can lead to severe pain as well as neurologic impairment from compression of the spinal cord or nerve roots, vertebral arteries, and anterior spinal artery. Severe involvement can lead to paralysis, stroke, and even death.

Pathogenesis

RA results from an autoimmune response that triggers the body to produce rheumatoid factor (RF), which is an IgM molecule directed against the autologous IgG antibody expressed by the synovium. RF is present in 80% of patients with RA. This activates macrophages and an increased production of monokines including interlukin-1 and tumor necrosis factor. Disruption of the synovial structures is caused by the release of activated metalloproteinases, including procollagenase and progelatinase. Osteoclasts are activated causing destruction of adjacent cartilage, tendons, and bone. Pannus is formed by granulation tissue formed within the reactive synovium by proliferating fibroblasts and inflammatory cells and is characteristic of the rheumatoid process.

Epidemiology

RA typically presents in patients in the fourth and fifth decades of life and is more common in females. The prevalence in the United States is 0.5% to 1% among whites. Approximately half are unable to work within 10 years of onset due to significant pain and disability. The cervical spine is involved in up to 95% of patients with RA. The spine is the initial site of RA diagnosis
in 10% of patients. Subluxation occurs in up to 86% of RA patients at some point over the disease course. Neurologic symptoms may be present in 11% to 58% of patients.

Classification

As with any disorder, a reliable classification system can assist with diagnosis, treatment recommendations, and research on clinical outcomes. The most recent classification system for RA is based on the 2010 American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) criteria. As opposed to earlier classification schemes, there has been a recent shift toward early treatment of RA based on the benefits of newer pharmacologic therapies. New additions to the criteria include acute-phase reactants and level-dependent consideration of autoantibody markers including anticitrullinated peptide antibodies (ACPAs). Table 24.1 shows the criteria for classification of RA.

Diagnosis

In the vast majority of cases, patients with RA involvement of the spine will have already been properly diagnosed due to involvement of the hands and feet. Patients with RA affecting the spine typically present with upper neck pain and stiffness as well as occipital headaches. The pain is typically worst in the morning and improves with activity. Headache occurs either through muscle spasms or by compression of the posterior rami of the greater and lesser occipital nerves. Patients with subluxation can report difficulty with maintaining an upright posture of the head. More severe cases can cause loss of consciousness, syncope, and vertigo. Spinal cord compression from either pannus formation or subluxation can result in myelopathy. Vertebral artery compression may cause cranial nerve palsies, visual disturbances, dizziness, ataxia, Horner syndrome, and dysarthria.

TABLE 24.1 2010 ACR/EULAR CLASSIFICATION CRITERIA FOR RHEUMATOID ARTHRITIS

	Joint Involvement	Score
A	1 large joint	0
	2–10 large joints	1
	1–3 small joints (with or without involvement of large joints)	2
	4–10 small joints (with or without involvement of large joints)	3
	>10 joints (at least one small joint)	5
B	Serology (at least one test result needed for classification)
	Negative RF and negative ACPA	0
	Low-positive RF or low-positive ACPA	2
	High-positive RF or high-positive ACPA	3
C	Acute-phase reactants (at least one needed for classification)
	Normal CRP and normal ESR	0
	Abnormal CRP or abnormal ESR	1
D	Duration of symptoms
	<6 weeks	0
	>6 weeks	1

TABLE 24.2 RANAWAT CRITERIA FOR PAIN AND NEUROLOGIC ASSESSMENT

Pain Assessment
Grade	Description
0	None
1	Mild; intermittent, requiring only aspirin analgesia
2	Moderate; a cervical collar was needed
3	Severe; pain could not be relieved by either aspirin or collar
Neural Assessment
Class	Description
I	No neural deficit
II	Subjective weakness with hyperreflexia and dysesthesias
IIIA	Objective findings of paresis and long tract signs but walking possible
IIIB	Quadriparesis with resultant inability to walk or feed oneself

The Ranawat criteria provide a scale for pain and neurologic function in patients with RA of the cervical spine as described in Table 24.2. If patients have not been previously diagnosed with RA, laboratory studies can include complete blood count, erythrocyte sedimentation rate, RF, and antinuclear antibody.

The initial imaging evaluation of the RA patient consists of anteroposterior, open-mouth odontoid, lateral, and flexion-extension radiographs of the cervical spine. Radiographic criteria to assess for instability include the following:

Anterior atlantodental interval (AADI) and posterior atlantodental interval (PADI) to assess for atlantoaxial instability (Fig. 24.1)
Chamberlain line, McCrae line, McGregor line, Ranawat index, Redlund-Johnell measurement, and/or Station of the atlas to assess for cranial settling (Figs. 24.2 and 24.3)
Subaxial canal diameter to evaluate for subaxial subluxation

Lateral flexion-extension radiographs are used to evaluate the AADI and PADI. The AADI is the distance
from the anterior aspect of the odontoid process to the posterior aspect of the anterior ring of the atlas. The PADI is the distance from the posterior aspect of the odontoid process to the anterior aspect of the posterior ring of the atlas. AADI can be used to determine the severity of anterior atlantoaxial subluxation. Anterior subluxation of 0 to 3 mm is normal in adults, but 3 to 6 mm of subluxation suggests instability due to disruption of the transverse ligament, and 9 mm or more suggests disruption of the periodontoid ligamentous and capsular structures with gross instability and the need for surgery. This measurement does not account for the possible presence of a pannus posterior to the odontoid process.

Figure 24.1 Diagram of the atlantoaxial joint showing the measurements for the anterior atlantoaxial interval (AADI), posterior atlantoaxial interval (PADI), and space available for the cord (SAC).

The PADI is a more accurate predictor of neurologic outcome. The spinal cord occupies 10 mm of the canal diameter, with 1 mm for the dura and 1 mm for spinal fluid on each side of the spinal cord for a total of 14 mm. Patients with a PADI of at least 14 mm have an improved likelihood of neurologic recovery following stabilization, while those with a PADI less than 10 mm are at risk of poor recovery.