Ревматоидный артрит атланто аксиального сочленения

The most common sites of rheumatoid arthritis (RA) are the metatarsophalangeal joints, followed by the metacarpophalangeal joints and the cervical spine (ankylosing spondylitis, rheumatoid spondylitis). Much of the understanding of spinal afflictions in rheumatoid arthritis was advanced by studies published in the 1950s and 1960s.[1] In 1951, Davis and Markley detailed medullary compression as a cause of death in patients with rheumatoid arthritis.[2] In 1969, Mathews reported that 25-30% of patients with rheumatoid arthritis who were admitted to the hospital had radiographic evidence of cervical spine involvement.[3]

Rheumatoid spondylitis (ankylosing spondylitis) primarily affects the cervical spine. Affliction of the thoracic or lumbar spine is rare. The anatomic abnormalities occur as a consequence of the destruction of synovial joints, ligaments, and bone. Abnormalities of the rheumatoid cervical spine generally can be grouped into 3 categories that may be seen in isolation or combined involvement, of which atlantoaxial instability (AAI) or atlantoaxial subluxation (AAS) is the most common abnormality (see the image below). AAS can be a fixed deformity or can be partially or fully reducible.

Rheumatoid spondylitis. Depiction of anterior subluxation of C1 on C2, retrodental pannus, and osseous erosions; the spinal cord is compressed between the pannus anteriorly and the posterior arch of the atlas.

Superior migration of the odontoid (SMO) is the next most common abnormality and has alternately been referred to as cranial settling, pseudobasilar invagination, or vertical/upward translocation of the odontoid (see the following images).[4] The third and least common deformity is subaxial subluxation, which may be seen at multiple levels and produces a stepladder deformity.

Rheumatoid spondylitis. Depiction of superior migration of the odontoid into the foramen magnum with compression of the spinal cord.

Rheumatoid spondylitis. Pertinent measurements of superior migration of the odontoid; cranial migration distance (CMD).

For patient education information, see eMedicine’s Arthritis Center, as well as Rheumatoid Arthritis and Rheumatoid Arthritis Medications.

Go to Rheumatoid Arthritis and Ankylosing Spondylitis for more information on these topics.

Numerous investigators have attempted to elucidate the natural history of rheumatoid arthritis as it affects the cervical spine (rheumatoid spondylitis, ankylosing spondylitis), with wide variation in their findings.[5, 6, 7, 8, 9]

Of the 0.8% of the white population in the United States and Europe affected by rheumatoid arthritis, neck pain is reported in 40-88% of patients. The prevalence of cervical spine involvement (rheumatoid spondylitis, ankylosing spondylitis) in rheumatoid arthritis ranges from 25% to 80%, depending on the diagnostic criteria applied.[10] However, only 7-34% of patients with rheumatoid arthritis have a neurologic deficit. A substantial number of patients with radiographic instability or neck pain do not develop neurologic deficits.[11]

Involvement of the cervical spine typically begins early in the disease process and often parallels the extent of peripheral disease. Of the 3 types of involvement, atlantoaxial instability (AAI) is the most common, occurring in up to 49% of patients.[12] Whereas most of these subluxations are anterior, approximately 20% are lateral and approximately 7% are posterior. Superior migration of the odontoid (SMO) is seen in up to 38% of patients with rheumatoid arthritis. Subaxial subluxation is seen as a discrete pathologic entity in 10-20% of patients.

Subaxial subluxation also develops after previous upper cervical fusions.[13, 14] In one series of 79 patients, 36% developed subaxial subluxation at an average of 2.6 years following occipitocervical fusion, and 5.5% experienced subaxial subluxation an average of 9 years following atlantoaxial fusion.[13]

Recent theories on the pathogenesis of rheumatoid arthritis suggest that the synovial cells of these patients chronically express an antigen that triggers the production of rheumatoid factor (RF), an immunoglobulin molecule directed against other autologous immunoglobulins. An inflammatory response is initiated, involving immune complex formation, activation of the complement cascade, and infiltration of polymorphonuclear leukocytes. The proliferating fibroblasts and inflammatory cells produce granulation tissue, known as rheumatoid pannus, within the synovium. The pannus produces proteolytic enzymes capable of destroying adjacent cartilage, ligaments, tendons, and bone. The destructive synovitis results in ligamentous laxity and bony erosion with resultant cervical instability and subluxation.[15, 16]

Atlantoaxial subluxation results from erosive synovitis in the atlantoaxial, atlanto-odontoid, and atlanto-occipital joints and the bursa between the odontoid and the transverse ligament (see the image below).

Rheumatoid spondylitis. Depiction of anterior subluxation of C1 on C2, retrodental pannus, and osseous erosions; the spinal cord is compressed between the pannus anteriorly and the posterior arch of the atlas.

The superior migration of the odontoid is attributed to erosion and bone loss in the occipitoatlantal and atlantoaxial joints (see the following images).

Rheumatoid spondylitis. Depiction of superior migration of the odontoid into the foramen magnum with compression of the spinal cord.

Rheumatoid spondylitis. Pertinent measurements of superior migration of the odontoid; cranial migration distance (CMD).

Subaxial subluxation results from destruction of the facets, intervertebral discs, and interspinous ligaments. Unlike degenerative disease, involvement of C2-C3 and C3-C4 is common, and osteophytes are seldom seen.

Rheumatoid involvement of the cervical spine (rheumatoid spondylitis, ankylosing spondylitis) is just one element in a systemic disease process. Cervical involvement often correlates with the degree of hand and wrist erosion. Cervical involvement also has been associated with the presence of rheumatoid nodules and the use of corticosteroids. Classically, craniocervical neck pain often is associated with occipital headaches.

Symptoms

Compression of the C2 sensory fibers supplying the nucleus of the spinal trigeminal tract can cause facial pain. Compression of the C2 sensory fibers supplying the greater auricular nerve may result in ear pain. Occipital neuralgia results from compression of the C2 sensory fibers supplying the greater occipital nerve. A history of myelopathic symptoms should be sought carefully. Patients may experience weakness, decreased endurance, gait difficulty, paresthesias of the hands, and loss of fine dexterity. Patients with involvement may experience and, eventually, incontinence.

Vertebrobasilar insufficiency may be found, particularly in patients with atlantoaxial instability (AAI). Complaints may include vertigo, loss of equilibrium, visual disturbances, tinnitus, and dysphagia. Similar symptomatology can also be caused by mechanical compression of the brainstem. In some patients, neck motion can elicit shocklike sensations through the torso or into the extremities (ie, Lhermitte sign).

Physical findings

The physical inventory of these patients frequently is confounded by the severity of their peripheral rheumatoid involvement. Weakness in these patients can also be due to tenosynovitis, tendon rupture, muscular atrophy, peripheral nerve entrapment, or articular involvement, making neurologic impairment less obvious. Signs of myelopathy should raise suspicion of cervical involvement. Rarely, cranial nerve dysfunction can occur secondary to compression of the medullary nuclei by the odontoid. Other rare findings in patients with advanced brainstem compression include vertical nystagmus and Cheyne-Stokes respirations.

The Ranawat classification can be used to categorize patients with rheumatoid myelopathy based on their clinical history and physical findings (see below).[17] This classification has some utility in determining the potential for neurologic recovery following surgery and is categorized as follows[17] :

• Class I — No neural deficit

• Class II — Subjective weakness, dysesthesias, and hyperreflexia

• Class IIIA — Objective weakness and long-tract signs; patient remains ambulatory

• Class IIIB — Objective weakness and long-tract signs; patient no longer ambulatory

Rheumatoid factor seropositivity has been correlated with more extensive cervical involvement (rheumatoid spondylitis, ankylosing spondylitis). The use of the rheumatoid factor as a predictor of neurologic involvement has not been established; therefore, it does not have a role in the surveillance of patients with rheumatoid arthritis with cervical involvement.

All patients with rheumatoid arthritis should have radiographic examination of the cervical spine because cervical involvement (rheumatoid spondylitis, ankylosing spondylitis) can remain asymptomatic. Imaging modalities include plain radiography, magnetic resonance imaging (MRI), polytomography, and computed tomography (CT) scanning. Although prediction of the onset of myelopathy in any particular patient is difficult, studies of large populations of patients have sought to establish parameters for predicting neurologic involvement via imaging studies.[11, 18, 19]

The initial imaging assessment in suspected rheumatoid spondylitis should consist of plain radiographs of the cervical spine, including lateral flexion and extension views. Several measurements that can help direct management can be made on plain radiographs.

AADI measurement

Traditionally, the anterior atlantodental interval (AADI) has been used to monitor patients with rheumatoid arthritis over time. This measures the interval from the posterior margin of the anterior ring of C1 to the anterior surface of the odontoid. An interval of more than 3 mm in an adult or 4 mm in a child is considered abnormal. Various authors have recommended surgery for values of more than 8 mm, 9 mm, or 10 mm (see Surgical Management).

Although the AADI was used commonly to monitor patients with cervical involvement, a number of investigations have shown that the AADI does not reliably discriminate between patients who are neurologically intact from those with neural deficit.[20] This is due in part to the 3-dimensional changes that take place with progressive subluxation. As the deformity progresses, the anterior arch of the atlas displaces in an anteroinferior direction as superior migration of the odontoid (SMO) combines with atlantoaxial instability (AAI). With continued SMO, the AADI decreases, although this vertical translocation is associated with a more unfavorable prognosis.

Boden and associates demonstrated this pitfall by examining the sensitivity, specificity, accuracy, and positive and negative predictive values of the AADI in predicting paralysis based on varying critical intervals (see the table below).[21] For example, raising the cut-off value for the AADI from 8 mm to 10 mm increases the specificity from 58% to 90%. However, the sensitivity with such a change in threshold value decreases from 59% to 35%. More recently, the posterior atlantodental interval (PADI) has been recommended as a more reliable predictor of whether neurologic compromise will develop.

Table. Reliability of the Anterior (AADI) and Posterior (PADI) Atlantodental Intervals in Predicting Paralysis in Patients with Rheumatoid Arthritis (Open Table in a new window)

PADI measurement

Anterior atlantoaxial subluxation may also be assessed by the PADI measurement, as measured from the posterior aspect of the odontoid to the anterior margin of the lamina of C1. Because the synovial pannus may occupy 1-3 mm of the retro-odontoid space, this interval does not represent the true space available for the cord.

The PADI was compared with the traditional anterior interval in a long-term series involving 73 patients.[21] Using a critical PADI of 14 mm or less resulted in a sensitivity (ability to detect those with paralysis) of 97%, a level superior to that using the AADI (see the table above). More importantly, the negative predictive value, using a critical PADI of 14 mm, rises to 94%. Therefore, if the PADI is greater than 14 mm, there is a 94% chance that the patient will not have paralysis. Such a high negative predictive value makes the PADI extremely reliable as a screening test.

SMO assessment

A variety of measurements have been used to assess SMO. All of these measurements attempt to identify and grade the degree of odontoid encroachment on space normally occupied by the spinal cord and brainstem. Unfortunately, many of these are difficult to reproduce. The image below depicts a few pertinent measurements.

Rheumatoid spondylitis. Pertinent measurements of superior migration of the odontoid; cranial migration distance (CMD).

The McGregor line has become the most consistent reference, because it connects the posterior margin of the hard palate to the most caudal point of the occiput. Vertical settling is defined here by migration of the odontoid by more than 4.5 mm above this line.

The Redlund-Johnell line assesses the occiput-to-C2 complex. The value measures the distance between the midpoint of the inferior margin of the body of the axis to the McGregor line. Values less than 34 mm in males and 29 mm in females are considered abnormal and correlate with increased risk of neurologic injury.[22]

The Ranawat index targets disease in the C1-C2 segment by utilizing a lateral radiograph. A line is drawn from the pedicles of C2 superiorly along the vertical axis of the odontoid until it intersects a line connecting the anterior and posterior arches of C1. A value less than 13 mm is diagnostic of vertical settling.

The McRae line connects the front of the foramen magnum to the back. The upper tip of the odontoid process should not project above this line and should normally be 1 cm below the anterior margin of the foramen magnum.

The Chamberlain line is drawn from the posterior margin of the hard palate to the posterior margin of the foramen magnum. Projection of the tip of the odontoid 6 mm above this line is considered pathologic. However, the margins of the foramen magnum are frequently difficult to delineate without a tomogram.

Subaxial vertebral subluxations

Plain radiographs are also useful in detecting subaxial vertebral subluxations. These subluxations may be quantitated on lateral cervical radiographs as translation forward in millimeters or as a percentage slip of the total anteroposterior diameter of the inferior vertebral body. Historically, focus was directed on the number of millimeters of listhesis or the percentage of vertebral slip. However, recent demonstrations show that the sagittal diameter of the subaxial canal correlates with the presence and degree of paralysis more often than does the percentage of vertebral slip. Patients with canal diameters of 13 mm or less are at higher risk for neurologic involvement.

The following image depicts a cervical radiograph from a patient with combined SMO and subaxial subluxation who underwent Occipitocervical fusion and lateral mass plating.

Rheumatoid spondylitis. Occipitocervical fusion combined with lateral mass plating for a patient with combined superior migration of the odontoid and subaxial subluxation. Courtesy of Steven R. Garfin.

Magnetic resonance imaging (MRI) has provided an increased ability to visualize the extent of spinal cord compression, particularly when due to pannus.[23] Dvorak and colleagues showed that two thirds of patients with atlantoaxial subluxation (AAS) have a pannus of greater than 3 mm in diameter.[24] Therefore, the bony canal diameter measured on plain radiographs may not represent the true space available for the cord. Kawaida et al demonstrated spinal cord compression in all patients with rheumatoid arthritis when the space available for the cord (as measured on MRI) was 13 mm or less.[25]

Using MRI, the cervicomedullary angle is an effective indicator of cord distortion from superior migration of the odontoid (SMO). This angle incorporates lines drawn along the anterior aspects of the cervical cord and along the medulla. The normal range is 135-175°. Angles less than 135° indicate basilar invagination and have been associated with myelopathy (see the image below for a patient example).

Rheumatoid spondylitis. MRI of a patient with superior migration of the odontoid and subaxial subluxation. Courtesy of Steven R. Garfin.