Disclosure
History of the Procedure: The most common sites of rheumatoid arthritis (RA) are the metatarsophalangeal joints, followed by the metacarpophalangeal joints and the cervical spine. Much of the understanding of spinal afflictions in RA was advanced by studies published in the 1950s and 1960s. In 1951, Davis detailed medullary compression as a cause of death in patients with RA. In 1969, Matthews reported that 25-30% of patients with RA who were admitted to the hospital had radiographic evidence of cervical spine involvement. Problem: RA 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. Atlantoaxial instability (AAI) or atlantoaxial subluxation (AAS) is the most common. AAS can be a fixed deformity or can be partially or fully reducible. Superior migration of the odontoid (SMO) is the next most common abnormality and has been alternately referred to as cranial settling, pseudo-basilar invagination, or vertical/upward translocation of the odontoid. The third and least commonly seen deformity is subaxial subluxation. This may be seen at multiple levels, producing a stepladder deformity. The 3 deformities may be seen in isolation, or combined involvement may occur. Frequency: RA affects 0.8% of the white population in the United States and Europe. Neck pain is reported in 40-88% of patients with RA. The prevalence of cervical spine involvement in RA ranges from 25-80%, depending on the diagnostic criteria applied. However, only 7-34% of patients with RA have a neurologic deficit. A substantial number of patients with radiographic instability or neck pain do not develop neurologic deficits. 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, AAI is the most common, occurring in up to 49% of patients. While most of these subluxations are anterior, approximately 20% are lateral and approximately 7% are posterior. SMO is seen in up to 38% of patients with RA. Subaxial subluxation is seen as a discrete pathologic entity in 10-20% of patients. Subaxial subluxation also develops after previous upper cervical fusions. In one series of 79 patients, 36% developed subaxial subluxation an average of 2.6 years following occipitocervical fusion, and 5.5% experienced subaxial subluxation an average of 9 years following atlantoaxial fusion. Pathophysiology: Recent theories on the pathogenesis of RA suggest that the synovial cells of these patients chronically express an antigen that triggers the production of rheumatoid factor, 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. Atlantoaxial subluxation results from erosive synovitis in the atlantoaxial, atlantoodontoid, and atlantooccipital joints and the bursa between the odontoid and the transverse ligament (see Image 1). The superior migration of the odontoid is attributed to erosion and bone loss in the occipitoatlantal and atlantoaxial joints (see Image 2). 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 seldom are seen. Clinical: Rheumatoid involvement of the cervical spine 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. 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 carefully sought. Patients may experience weakness, decreased endurance, gait difficulty, paresthesias of the hands, and loss of fine dexterity. Patients who are involved may experience urinary retention and, eventually, incontinence. Vertebrobasilar insufficiency may be found, particularly in patients with AAI. Complaints may include vertigo, loss of equilibrium, visual disturbances, tinnitus, and dysphagia. Similar symptomatology also can 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). The physical inventory of these patients frequently is confounded by the severity of their peripheral rheumatoid involvement. Weakness in these patients also can 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). This classification has some utility in determining potential for neurologic recovery following surgery. The Ranawat classification of neurologic deficit is as follows:
Numerous investigators have attempted to elucidate the natural history of RA as it affects the cervical spine, with wide variation in their findings. Depending on the diagnostic criteria applied, the prevalence of cervical involvement in RA ranges from 25-80%. The likelihood of cervical involvement appears to increase with the duration of rheumatic disease. Because neurologic deficit is seen only in 7-34% of cases, many patients with pain and radiographic criteria for instability do not develop neurologic sequelae. However, 10% of patients with RA may die from brainstem compression that is unrecognized before their sudden death. The identification of a subset of patients with impending neurologic deficit has been elusive due to the poor correlation of neurologic symptoms with radiographic indicators of instability. Therefore, universally accepted surgical indications have been slow to develop.
Contraindications: Contraindications to surgery include medical conditions that suggest the patient would not tolerate the stress of surgery, such as unstable angina or a recent myocardial infarction or stroke. Active infection with likely bacteremia would also be a relative contraindication to surgery, especially in the setting of planned instrumentation. The patient's medical condition should be optimized prior to proceeding with any planned surgical intervention. |
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Lab Studies:
Imaging Studies:
Medical therapy: An approach to surgical and nonsurgical management can be developed based on the natural history of rheumatoid involvement of the cervical spine and radiographic predictors of paralysis. As suggested by Boden et al, 3 goals should be kept in mind. The first goal is to avoid the development of an irreversible neurologic deficit, as patients with more severe deficits have less recovery and higher morbidity. A second goal is to prevent sudden death from unrecognized neural compression, as has been reported in up to 10% of deaths in RA. Finally, as half of patients with RA with radiographic evidence of instability remain asymptomatic, it is best to avoid surgery if the patient can be identified as being one who will most likely not develop neurologic problems. Nonsurgical treatment Nonoperative treatment of rheumatoid involvement of the cervical spine is supportive. Early aggressive medical management is important in the global sense, as cervical involvement has been correlated with disease activity. Collars can be used for comfort purposes. Rigid cervical collars most likely do not prevent subluxation; however, they may prevent reduction of a deformity by limiting extension. Skin sensitivity in this population also causes problems with rigid orthoses. Patients being monitored need careful surveillance for long tract signs or for radiographic findings suggesting impending neurologic compromise. Surgical therapy: Patients with refractory pain, clearly evident neurologic compromise, or intrinsic spinal cord signal changes on MRI generally are candidates for surgical intervention. The controversy surrounds the treatment for patients with little or no pain, no neural deficit, and radiographs suggestive of instability. To facilitate understanding of the operative indications and perioperative details, categorization of these patients by their pathologic lesion is helpful. Atlantoaxial subluxationPreoperative details Patients with AAS and no symptoms or signs of myelopathy can be observed when the PADI on the lateral cervical radiograph is more than 14 mm. Those who have a PADI that measures less than 14 mm should have an MRI scan to determine the true space available for the cord. MRI findings of less than 13 mm of space available for the cord and a cervicomedullary angle of less than 135° generally are indications for surgical stabilization. Intraoperative details The type of procedure performed is determined by whether or not the subluxation is reducible, the individual surgeon's preference and experience, and the patient's condition. If the deformity is reducible, posterior atlantoaxial fusion can be accomplished by a variety of techniques. Gallie reported a technique for posterior atlantoaxial arthrodesis in 1939, a technique that has been used with different modifications since that time. The procedure essentially consists of a block of autologous bone graft fixed by wire loop to the posterior arch of the atlas and the spinous process of the axis (see Image 5). While technically straightforward to perform, rotational stability and translational stability are inferior to other techniques. The Brooks fusion uses 2 posterior paramedian autologous structural grafts, usually attached with sublaminar wires (see Image 6). The bilateral fixation improves rotational stability. Multistrand titanium cables are increasingly favored over monofilament stainless steel wires because of improved strength and ease of contouring, as well as postoperative MRI and CT scan imaging qualities. All techniques using sublaminar wire or cable fixation have the potential risk of spinal cord injury during passage or from late failure of the implants. Additionally, the posterior arch of the atlas may be osteoporotic or partially deficient, thereby limiting its use. Immediate multidirectional stability can be achieved by C1-C2 transarticular screw fixation. The screws are inserted posteriorly by entering the inferior aspect of the facet of C2, crossing the C1-C2 facet joint, and then entering into the lateral mass of C1 (see Image 7). Safe insertion requires thorough understanding of the upper cervical anatomy and exposure of the medial border of the C2 pedicle. A preoperative CT scan should carefully be reviewed because some C2 pedicles may have a small diameter, the lateral mass may be partially resorbed, or the vertebral artery may course superomedially. These conditions preclude safe transarticular screw placement. If there is good bone in the lateral masses, the patient may require only a cervical collar. However, patients with poor fixation may require a halo device postoperatively. Patients with irreducible deformity and posterior compression can be treated with a C1 laminectomy and transarticular stabilization. Patients who have irreducible deformity and bony anterior compression may be decompressed by an anterior transoral approach, particularly in end-stage conditions. This route has several difficulties, such as limited opening of the mouth in patients with concomitant temporomandibular disease, postoperative infection, and pharyngeal mucosal edema. However, several authors have reported good results using this procedure. This technique generally is followed by posterior stabilization as a 2-stage same-day procedure. Patients who are healthier (Ranawat class I and class II) may be adequately treated with atlantoaxial stabilization and fusion alone, even in the presence of irreducible deformity. Some authors recommend that patients with anterior cord compression from proliferative retrodental pannus be treated with ventral transoral decompression. However, recent data has documented resorption of retrodental pannus if a stable posterior fusion is achieved. Of these options, initial treatment with a posterior fusion followed by MRI and clinical follow-up is the most commonly performed. If the pannus does not resorb and neurologic deficit persists, late transoral decompression can be performed. Superior migration of the odontoidPreoperative details Even in the absence of neurologic deficit, patients with any degree of basilar invagination should have an MRI in flexion to evaluate spinal cord compression. Surgical treatment should be considered in any patient with cord compression or neurologic deficit. Preoperatively, cervical traction can be used to attempt a gradual reduction. Intraoperative details Occipitocervical fusion is the procedure of choice in patients with SMO. Several devices have been described, ranging from wire loops securing tricortical bone graft supplemented with cement or metal mesh, contoured rods, and more recently, plates and screws (see Image 8). The more rigid fixation afforded by plating has been associated with a lower pseudarthrosis rate when compared to wiring techniques. Occipitocervical fusion with plating generally involves screw placement into the C2 pedicles under fluoroscopic guidance through a precontoured plate. This allows easier subsequent placement of subaxial screws in the lateral masses and in the occiput. Screws usually are not placed above the inion to avoid the intracranial venous sinuses. While the inner table can be thin in places, holes drilled 2-3 cm from the midline, halfway between the foramen magnum and the transverse sinus, generally are safe. No matter what implant technique is used, autologous bone grafting always should be performed. If the deformity is irreducible in traction, decompression either posteriorly or anteriorly (based on the location of the compression) should be considered as an adjunct to the fusion, as discussed above. Anterior compression in these patients is predominantly osseous, not from synovial pannus. Therefore, a ventral route provides more reliable decompression. Subaxial subluxationPreoperative details Patients with subaxial subluxation and no evidence of neurologic deficit can be observed. Plain radiographs are sufficient for surveillance. Patients with a bony canal diameter less than 14 mm should have an MRI to evaluate the true space available for the cord. If the space available for the cord is less than 13 mm or if significant segmental hypermobility is present, surgical consideration is warranted. Intraoperative details Most patients with subaxial subluxation can be treated with posterior cervical fusion using autograft bone. Internal fixation with wires, plate-screw, or rod-screw constructs allows for earlier mobilization and increased rates of fusion. Patients with irreducible subluxations or significant neurologic deficit may be best treated with anterior decompression and fusion alone or in concert with posterior fusion. Combined subluxationsPreoperative details Some patients may have upper cervical involvement as well as early subaxial subluxation. In these instances, the fusion should be extended to include the involved subaxial segments to avoid early deterioration of borderline subluxations below a rigid upper cervical fusion (see Image 8). Postoperative details The type of orthosis used postoperatively often is best determined on an individualized basis. Many patients have porotic bone of both the posterior elements and of the structural graft harvested from the iliac crest. Upper cervical fusions in such patients may be best managed postoperatively in a halo. When rigid collars are used, careful surveillance of the skin is mandatory to avoid decubiti. Also, if temporomandibular joint (TMJ) involvement is present, eating (chewing) may be a problem in a cervical-thoracic orthosis (CTO). Follow-up care: Even after achieving a successful fusion, patients with RA must continue to have long-term follow-up. Subaxial instability can develop below upper cervical fusions, so radiographic follow-up should be obtained periodically even in patients who are asymptomatic. For excellent patient education resources, visit eMedicine's Arthritis Center. Also, see eMedicine's patient education articles Rheumatoid Arthritis and Understanding Rheumatoid Arthritis Medications.
RA is a systemic disorder, and patients may have varying degrees of generalized debilitation. The postoperative course of such patients can be complicated by fragile skin and poor wound healing. Poor preoperative nutritional status and corticosteroid dependence may potentiate wound-healing problems and predispose toward infection. Some airways are difficult to intubate. Excessive trauma during intubation may be responsible for postoperative breathing problems. Wattenmaker reported a 14% incidence of upper airway obstruction after extubation in patients intubated without fiberoptic assistance, compared with a 1% incidence in patients intubated fiberoptically. The perioperative mortality rate has been reported to be as high as 5-10%.
Cervical fusion in RA has a clinical success rate of 60-90%. This wide range is partly due to the definition of clinical success and by variation in disease severity at the time of surgery. Rates of neurologic improvement also vary widely, ranging from 27-100%. Peppelman et al reviewed the neurologic recovery in 90 patients with neurologic deficits who underwent surgery for rheumatoid deformity of the cervical spine. The investigators reported that 95% of patients treated for AAS improved at least one Ranawat grade, 76% of patients with combined AAS and SMO improved, and 94% of those treated for isolated subaxial subluxation improved. Age, gender, duration of paralysis, preoperative ADI, and percentage of slippage in subaxial subluxations all have been found to have no correlation with neurologic recovery. The degree of preoperative neurologic deficit has been shown to correlate with neurologic recovery. The results appear to be less favorable in patients with more advanced preoperative neurologic deficits. Casey and colleagues reported their results after surgery in patients classified as Ranawat Class III. Fifty-eight percent of ambulatory patients (grade IIIA) attained a grade I or grade II after surgery. Conversely, only 20% of nonambulatory patients (grade IIIB) improved to grade I or grade II postoperatively. Radiographic parameters also have been shown to predict postoperative neurologic recovery. Boden et al reported that patients with AAS whose posterior ADI was less than 10 mm before surgery had poor return of motor function. With superimposed SMO, clinically significant neurologic recovery was seen only when the PADI was at least 13 mm prior to surgery. For patients with subaxial subluxations, less recovery was seen in those with a residual postoperative subaxial canal diameter of less than 14 mm. Nonunion rates in this population have been estimated at 5-20%. Many of these nonunions may be asymptomatic, so management should be individualized.
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