a b c d Figure 1. Horizontal and Vertikal Instability a, c Normal anatomy of the occipitocervical junction. b Advanced stage of instability and resorption of the lateral masses of the atlas. The dens axis moves upward into the foramen magnum. d Horizontal instability in the atlantoaxial segment with decreased posterior atlantodental interval and increasing anterior atlantodental interval. Vertical instability with upward migration of the dens into the foramen magnum. Classification The commonly used classification is the Ranawat classification [20], which dif- ferentiates between the different stages of the rheumatoid influence on the patient’s mobility ( Table 1). This relatively crude differentiation is hardly able to assess the situation of these patients satisfactorily. Important items such as hygienic independence, eating capacities and general use of the hands are not included in the classification, but are of the utmost importance to the patient. Therefore the classification is barely sufficient to serve as an outcome measure- ment of surgery. For the practical clinical user, the recently published and vali- dated Core Questions [17] have proven to be a useful basis for assessment. Table 1. Ranawat classification Class I Pain, no neurological deficit Class II Subjective weakness, hyperreflexia, dysesthesias Class III Objective weakness, long-tract signs Class IIIA Ambulatory Class IIIB Non-ambulatory 1044 Section Tumors and Inflammation Clinical Presentation The radiological alterations in RA do not correlate with the symptoms As known from other conditions in the spine, radiological changes are not always concordant with the clinical symptomatology. Therefore major instabilities may be without symptoms, and minor alterations may be very painful. History The history of RA is generally evident when the spine becomes involved. There- fore, diagnosis does not cause any clinical problems. The cardinal symptom of atlantoaxial instability is: suboccipital pain pain exacerbation on head rotation or flexion Sometimes a painful “clunk” may be heard or felt by the patient or the examiner during examination. If vertebr obasilar insufficiency is involved, patients complain about: tinnitus vertigo disturbance of visual orientation dysphagia Physical Findings Pain can be so severe that a physical exam is not possible Often occipital and neck pain are so severe that clinical examination is almost impossible due to protective muscle spasms. Neurological involvement with compression of the brainstem and the medulla oblongata may be demonstrated by a positive Lhermitte sign: The patient complains of a sharp electric pain irra- diation in the body during a flexion maneuver of the cervical spine. Myelopathic symptoms occur in chronic instability due to repetitive trauma of the medulla. Typically, the clinical manifestation expresses itself by: a positive scapulohumeral reflex [21] atrophy of the small muscles of the hand [19] Cervical RA can cause myelopathy However, in RA patients myelopathic symptoms may be difficult to detect clini- cally due to multiple alterations on various joints from frequent surgical inter- ventions, thus making it critical to assess reflexes or muscle tonus. In these cases, neurophysiological investigations with electrophysiological examinations are indispensable. Diagnostic Work-up Imaging Studies Standard Radiographs Standard radiography is the initial imaging modality of choice Conventional radiographs are standard. Views in the lateral and anteroposterior (including the transoral anteroposterior view of the atlas) positions contain valu- able information about bone quality, segmental changes and alignment. Several lines that orientate at bony landmarks of the upper cervical spine allow the degree of subluxation and vertical migration to be quantified. Atlantoaxial instability may only be detected in lateral flexion/extension views. While in flex- Rheumatoid Arthritis Chapter 37 1045 Figure 2. Radiographic assessment of instability Reducibility of atlantoaxial subluxation influences surgical strategy ion the atlas slips anteriorly into a subluxed position, and in extension reduction an anatomical position occurs as long as there is no fixed subluxation. The trans- verse instability is measured by the anterior (ADI)orposterior(PA DI )( Fig. 2) atlantodental intervals ( Fig. 2). The information on reducibility will influence the strategy for the surgical procedure. The flexion view is also able to demonstrate segmental instability of the subaxial cervical spine. The presence of gross atlantoaxial instability requires fiberoptic intubation This information is not only valid for the surgeon who intends to assess the degree of instability but also for the anesthetist who has to intubate the patient. In the presence of gross instability, fiberoptic intubation is recommended in order not to move the neck. Magnetic Resonance Imaging MRI is indispensable for surgical planning This type of imaging represents the standard diagnostic procedure. It allows direct visualization of soft tissue and bone and the relation to the neurogenic tis- sue ( Case Stu dy 1). Myelon compression by pannus can only be detected on MRI. Ifthespaceavailableforthecord(SAC)inflexionislessthan6mm,theriskof myelopathy increases significantly [5, 6]. The precise anatomical details shown on the MRI scan are indispensable for the planning of the surgery. Information about the dimension of the isthmus of C2 may be crucial in deciding whether a transarticular screw fixation is suitable or not. Computed Tomography The information contained in the CT scan is able to reveal anatomical details of bony structures and CT is indicated as an additional investigation in complex cases with rotational deformities of the upper cervical spine. Ultrasound Ultrasound is useful as a screening method in cases where anomalies of the course of the vertebral artery are suspected, namely in significant destruction and deformities. 1046 Section Tumors and Inflammation a b c d e Case Study 1 A 52-year-old female patient had suffered from seropositive rheumatoid arthritis for 18 years. Medical treatment had been successful and the course was relatively benign. Both hips had been replaced 6 and 4 years previously. The patient had been feeling increasing neck pain for 9 months that had increased with physical activity and subsided at rest. Several weeks previously, the patient noted a noise in her neck when flexing the cervical spine, which increased the neck pain. The neurological investigation revealed no neurological deficit. The radiographs in flexion showed atlantoaxial instability with anterior subluxation of the atlas ( a). This dislocation was reduced to normal in the extension views (b). The MRI scan of the cervical spine showed mild degenerative changes in the lower cervical spine but no stenosis in the suboccipital area ( c). It was decided to fix the atlantoaxial instability with a transarticular C1/2 screw fixation and posterior bone graft ( d, e). Rheumatoid Arthritis Chapter 37 1047 Magnetic Resonance Angiography Magnetic resonance angiography is the method of choice for identification of anomalies of the vertebral artery. The details obtained about the vessel through this non-invasive technique allow optimization of the position of the screws for internal fixation. Injection Studies Facet Infiltration Facet joint infiltrations are helpful in localizing the pain source Also not commonly used in RA, facet infiltration may help to determine the source of pain. The injection of a small amount of local anesthetic into the facet joint should relieve the pain if the corresponding facet is the origin of pain. In cases with concomitant osteoarthritis of the atlantoaxial joints, this diagnostic procedure may be helpful to differentiate between pain originating from C1/2 and subaxial pain. Nerve Root Infiltration The placement of local anesthetics into the intervertebral foramen can help to separate peripheral nerve compression syndromes from compressive symptoms due to local stenosis at the cervical spine. Neurophysiological Investigations These investigations are performed by the neurologist and provide information about the localization and the extent and severity of myelopathy. These addi- tional techniques have a special place in the context of RA. The clinical examina- tion in severe RA may be extremely difficult to evaluate. Patients with severe RA have undergone multiple surgery with soft tissue repair and joint replacement during the course of the disease. Provocation of reflexes or the testing of muscle tonus might be impossible. The objective evaluation of these neurophysiological tests helps to determine the severity of the damage. Non-operative Treatment Thecourseofthe rheumatoid disease is unidirectional The course of the rheumatoid disease is unidirectional [18] (Case introduction). Recent medical treatment, i.e. the advent of TNF- inhibitors,isabletostoporto slow down the progression, but there is still no medication to restore stability, correct deformity or decompress the spinal canal. This knowledge includes the aspect of prophylaxis. Regular follow-ups are necessary to detect the progression of instability. Operative Treatment General Principles The general objectives of surgery include: eliminating instability restoring anatomical alignment decompressing neurological structures preventing adjacent segment decompensation 1048 Section Tumors and Inflammation Early surgery minimizes the operative risks If the intervention is performed at an advanced stage, the surgery is much more invasive, requiring anterior decompression/stabilization and additional poste- rior stabilization, while at an earlier stage of the deformity a relatively simple posterior approach would have the same effect. On the other hand, the patient probably has undergone multiple interventions and has more planned surgery ahead in his or her schedule. Prophylactic surgery will be hardly acceptable in this situation, but a regular work-up with imaging will be mandatory in order not to miss any progression of instability in the cervical spine. The same applies for the myelopathy. Repetitive traumatization of the myelon by instability can cause myelopathy. Once manifest, recovery becomes more unlikely. Early stabilization can prevent the occurrence of myelopathy. Indications The most frequent indications for surgery are: severe neck pain instability neurological symptoms It is important to note that instability of the atlantoaxial segment can occur with- out significant pain. If there is a clear progression with increasing atlantodental interval (ADI) in different follow-up investigations, stabilization should be planned even in the absence of severe pain. In unchanged situations, the patient should be given careful information and the possible risks and advantages of early surgery or a “wait and see” policy should be explained to involve the patient in the decision-making process. If myelopathic symptoms are present, decom- pressive and stabilizing surgery is indicated to prevent further damage [2, 5] ( Table 2): Table 2. Indications for atlantoaxial surgery based on imaging SAC in MRI (flexed position) Less than 6 mm PADI in flexion radiographs Less than 14 mm Distance from base of the corpus C2 to the fora- men magnum Less than 31.5 mm SAC = space available for cord; PADI = posterior atlantodental interval The patient’s general condition must be taken into account The decision on surgical indications and even on surgical strategy in rheumatoid patients should take into account the general situation and other surgery that might be planned. If inclusion of the occiput into the fusion of the cervical spine is considered necessary, the situation of the upper limbs should be carefully checked: In the presence of restricted elbow mobility, the postoperative situation with a smaller range of motion of the cervical spine may not allow a spoon and fork to be brought to the mouth and may lead to an inability to eat independently and therefore to a significant loss of independence for the patient. A careful re- Thefunctionoftheelbow and shoulder has to be taken into account when occipitocervical fusion is planned evaluation of the indication or synchronized surgery of the elbow will be neces- sary in this situation. Similarly if shoulder surgery and cervical surgery are planned in one sitting, it has to be taken into account that for shoulder surgery special positioning with head rotation is necessary. It should be carefully evalu- ated whether this rotation is tolerable in the presence of instability and whether the operated cervical spine is sufficiently stabilized. Rheumatoid Arthritis Chapter 37 1049 Surgical Techniques Upper Cervical Spine Atlantoaxial Stabilization The classic wiring techniques were introduced by Gallie in 1939 [8] and Brooks in 1978 [3] (see Chapter 30 ). Transarticular screw fixation (Magerl) is the method of choice for atlantoaxial instability One or two iliac bone grafts are inserted posteriorly and fixed with wires to the posterior arch of the atlas and the spinous process of C2 or the lamina of C2. The advantage of these procedures is the easy technique; however, the lack of stability mainly in rotation and translation leads to a considerable rate of pseud- arthrosis. Attempts have been made to improve this by introducing posterior clamps between the atlas and axis but these have failed because of frequent loos- ening. The technique of Magerl/Seemann (1986) [16] was finally able to improve the results of posterior atlantoaxial fusion by using transarticular screws ( Case Study 1 ). This procedure provides a three-dimensional stability [11, 12] by insertion of screws bilaterally through the facet joints, thus preventing disloca- tion in translation and rotation ( Fig. 3 ). The construct is completed by a poste- rior bone graft fixed with wires or non-absorbable suture to the atlas and axis in the midline. This additional posterior support provides stability in flexion and extension. It is possible to reduce the rate of pseudarthrosis to 0–5% with this procedure. The disadvantage remains the technically difficult insertion of the screws. An increased capacity for reduction in cases of fixed subluxation is achieved by lateral mass fixation in the atlas [9, 14]. Four polyaxial screws of appropriate size are inserted bilaterally into the lateral masses of the atlas and the pedicle of C2 and connected with longitudinal rods. This complex construct represents a difficult operative technique but is excellent for special cases and salvage procedures. ab Figure 3. Atlantoaxial fusion in RA a, b A midline bone graft is fixed posteriorly in the midline by a wire loop between the posterior aspect of C1 a and C2. Transarticular C1/C2 screw fixation. By inserting bilateral transarticular screws and a posterior bone graft in the midline, a solid three-point fixation is achieved between the atlas and the axis ( b). 1050 Section Tumors and Inflammation Occipitocervical Fusion Inclusion of the occiput often leads to subaxial decompensation As mentioned earlier, the inclusion of the occiput into the fusion mass in rheu- matoid patients should be carefully indicated. The increased lever arm produces additional forces to the adjacent levels. In RA patients with reduced bone quality, this leads to decompensation in the non-fused segment of the lower cervical spine in 30–40% of patients [15, 18]. As a consequence, the inclusion of the occi- put implies the extension of the fusion to the whole cervical spine, leading to a significant reduction in range of motion [13]. Decompression of the Upper Cervical Spine (C0–C2) The most frequent compression of the myelon occurs at the atlantoaxial level by the subluxation that causes a dens axis protruding dorsally into the lumen of the spinal canal. The easiest way to decompress therefore is to restore the normal anatomical situation by reducing the subluxation. This can be achieved during the fixation procedure if the subluxation has not yet been fixed by advanced joint destruction. In non-reducible dislocations, an anterior transoral approach may be used to decompress the spinal canal by resection of the dens [4]. Since this procedure requires partial resection of the anterior part of the atlas, additional fixation should be performed. In the same sitting, posterior atlantoaxial fixation can be added. This also allows posterior decompression by laminectomy or wid- ening of the foramen magnum if required ( Table 3): Table 3. Interventions of the upper cervical spine Pathology/intervention “Wait and see”, regular follow-up Stabilization C1/2 Transoral decompression Inclusion of the occiput Painfree, moderate C1/2 dislocation X C1/2 subluxation without myelopathy (X) X C1/2 reducible subluxation with myelopathy X Locked C1/2 subluxation with myelon compression X X Vertical migration of the dens without myelopathy X Vertical migration of the dens with myelopathy X X Subaxial Cervical Spine (C2–C7) Decompression of the Subaxial Spine Corpectomy is the preferred method for anterior decompression Narrowing of the spinal canal can occur by pannus formation or secondarily by segmental dislocation and malalignment. Due to the anatomical configuration, the cervical spine tends to produce anterior dislocation and loss of lordosis with mainly anteriorly located compression. The anterior decompression therefore represents the standard procedure. According to the severity of the stenosis, one or several levels are involved, requiring corpectomy with removal of the anterior part of the vertebral body ( Fig. 4). From a posterior approach, laminectomy can be added if posterior compression is identified. Stabilization of the Subaxial Cervical Spine Marked osteoporosis may require anterior and posterior fixation The administration of steroids over a period of years produces marked osteopo- rosis in rheumatoid patients, which represents a most challenging situation. Bone grafts, cages and plates tend to subside, producing recurrent deformation and pseudarthrosis. Therefore in most situations of multisegmental fusion, a Rheumatoid Arthritis Chapter 37 1051 a b c d Case Study 2 A 46-year-old female had suffered from seropositive rheumatoid arthritis for 11 years. Seven years previously she experi- enced an episode of mild neck pain. The radiographs at the time revealed an atlantoaxial subluxation in the flexion view ( a). Her treating physician considered conservative treatment appropriate. She underwent several interventions to the peripheral joints (hips, elbow, hand), but developed neck pain only 8 months previously. Four weeks previously she felt it difficult to maintain her head in an upright position and preferred to wear a collar for stabilization. She reported inter- mittent paresthesias in both hands. The radiograph of her cervical spine showed in the lateral view a kyphotic deformity involving C4–C6 ( b). Bone resorption and sclerosis of the endplates with resorbed discs were the morphological changes. The MRI scan confirmed the deformity and revealed a spinal stenosis at the level of C5/6 due to subluxation ( c). Neuro- physiological examination of the patient provided evidence of mild cervical myelopathy. The patient was surgically treated with anterior decompression by corpectomy C4–C7. The reconstruction of the anterior column was achieved by insertion of a titanium mesh cylinder. It was filled with the debris of the corpectomy bone and fixed in place with two bicortical bone screws. In the same session the posterior fixation from C0 to T2 was executed. Abundant iliac bone was used as fusion mass along the entire cervical spine ( d, e). 1052 Section Tumors and Inflammation ab Figure 4. Subaxial fusion in RA a, b Reduced bone quality in RA often requires complex surgery with anterior decompression by corpectomy, recon- struction with a cage or bone graft and posterior fixation with a screw rod system. combined anterior and posterior approach will be necessary to achieve sufficient stability ( Case Study 2).Anteriorly,platesandstrutgraftsarecommonimplants to compensate for the iatrogenic instability produced by corpectomy. Posteriorly, lateral mass screws and plate or rod fixation ( Fig. 4) provide sufficient stability. In special cases where additional reduction is required, the transpedicular screw fixation technique provides more stability but carries a higher risk of nerve root injury. Rheumatoid Arthritis Chapter 37 1053 . posterior arch of the atlas and the spinous process of C2 or the lamina of C2. The advantage of these procedures is the easy technique; however, the lack of stability mainly in rotation and translation. indispensable for surgical planning This type of imaging represents the standard diagnostic procedure. It allows direct visualization of soft tissue and bone and the relation to the neurogenic tis- sue. surgery with soft tissue repair and joint replacement during the course of the disease. Provocation of reflexes or the testing of muscle tonus might be impossible. The objective evaluation of these