There are multiple techniques by which to secure C1 to C2 posteriorly. Although the vast array of techniques is beyond the scope of this chapter, it is worth men- tioning the evolution in operative fixation techniques. Early on, methods described by Brooks, Gallie, and Sonntag utilized wiring techniques in conjunction with structural autograft. It was recommended that all patients wear a halo orthosis fol- lowing such treatments. Since that time, C1-2 transarticular screws have been used, which has been associated with a large improvement in rigidity and subsequent bony union (Tips from the Masters 10-5).7 However, one major anatomic limitation to the use of transarticular screws is the presence of a small C2 pars interarticularis.
In such cases, safe passage of a screw without injury to the vertebral artery may not be possible. For this reason, others have developed techniques by which C1 and C2 can be rigidly be fixated. Harms and Melcher8 described the placement
Basilar artery
Pons Invagination
of dens into medulla
Foramen magnum
Anterior arch of C1 (partial resection)
Beveled (~30°) tubular retractor
Neuroendoscope
Suction
Bur
Irrigation catheter
Cervical dura matter
Vertebral artery C3 C4
C2 C1
Surgical approach of tubular retractor
Clivus
FIGURE 10-4 Illustration of the transcervical endoscopic odontoidectomy as described by Wolinsky and co-workers.4
of C1 lateral mass screws and C2 pars interarticularis screws connected by rods.
Theoretically, the chance of vertebral artery injury may be decreased with such techniques (Tips from the Masters 10-6). Others since have also described various techniques of C2 fixation, including the use of C2 pedicle screws and C2 laminar screws.9,10
Tips from the Masters 10-5 • C1 screws should be bicortical. Gentle tapping and palpation must be done to avoid inadvertent injury to the carotid artery anterior to the spine.
Tips from the Masters 10-6 • C2 pedicle screws can be placed safely only after preoperative MRI or CT scans confirm the absence of large or aberrantly located vertebral arteries.
Regardless of the technique used for fixation, basic guidelines apply to posterior stabilization. First, fixation must be rigid, because the pannus represents instabil- ity. If the pannus is soft, it may regress over time with such fixation, although this may take months to years. Second, in cases of obvious gross instability, subluxation can be corrected posteriorly, which thus indirectly decompresses the spinal canal.
O’Brien and co-workers11 described intraoperative reduction of C1-2 subluxation via manipulation of posterior instrumentation in C1 and C2. Third, all anterior decom- pressive procedures require posterior fixation. Thus, after an anterior approach, the spine should be assumed to be extremely unstable, due to resection of the atlanto- dental articulation. In such cases patients require rigid external immobilization until posterior instrumentation can be implanted.
The patient was offered surgical treatment for her condition via a posterior route. She consented to the operation and underwent a C1-2 instrumented fusion with use of allograft. C1 lateral mass screws and C2 pedicle screws were placed and fixed via small rods in the standard fashion as described by Harms and Melcher8 (Figure 10-5). Ideal placement of the hardware was then confirmed postoperatively with a CT scan (Figure 10-6). The patient did well during and after surgery. Follow-up over the last 2 years has shown durable relief of her neck pain and no signs of myelopathy. Recent MRI done 18 months after surgery shows a stable construct and absence of spinal cord or lower brainstem compression (Figure 10-7).
FIGURE 10-5 Intraoperative lateral radio- graph taken after placement of C1 lateral mass screws and C2 pedicle screws and rod fixation.
DISCUSSION OF BEST EVIDENCE
Arthritis of the atlantodental joint leading to a pannus is most commonly caused by rheumatoid arthritis. Degenerative osteoarthritis is a less common cause and, in gen- eral, less progressive. As a result, most attention in the literature has been given to pannus associated with rheumatoid arthritis, and it is on the findings of these studies that most of the recommendations are based. In treating a patient with a pannus, the patient must first be evaluated fully via history taking, physical examination, and radiography.
FIGURE 10-6 Sagittally reconstructed CT scan showing placement of the C1 lateral mass and C2 pedicle screws.
A B
FIGURE 10-7 T2-weighted sagittal (A) and axial (B) MRI scans of the cervical spine showing stability of a C2 pannus and absence of spinal cord and lower brainstem compression.
Based on history, potential risk factors for progression of a rheumatoid pannus have been identified.12 Nonradiographic risk factors include male gender, rheuma- toid factor seropositivity, and the prolonged use of corticosteroids for treatment of rheumatologic disease.13 Based on clinical progression of neurologic dysfunc- tion, Ranawat and colleagues14 classified patients into three categories to define the extent of myelopathy and plan treatment. Class I patients have no neurologic dysfunction. Class II patients have subjective weakness with hyperreflexia and dys- esthesias. Class III patients have objective weakness and long-tract signs. These patients were further subcategorized into class IIIA patients, who are ambulatory, and class IIIB patients, who are no longer ambulatory. Higher classifications are associated with worse neurologic outcomes with or without surgical intervention.
Radiographic measurements have been traditionally based on plain radiographs and have included measurements such as the anterior atlantodental interval, the pos- terior atlantodental interval, and superior migration of the dens past the McGregor line (the line connecting the hard palate to the occiput). However, Riew and associ- ates recently found that no single test reliably assessed C1-2 deformity associated with rheumatoid arthritis and concluded that a number of measurements should be considered together to evaluate patients.15 With the more common use of MRI, space around the spinal cord can be evaluated directly and not indirectly from plain radiographs. It is therefore now generally agreed that 13 mm of space is needed at the C1-2 junction in the adult patient to allow the spinal cord to be free from compression.16
Once the patient is evaluated clinically and radiographically, options for treat- ment can be provided to the patient. Currently, there is no randomized controlled trial comparing the results of conservative versus surgical management. In addition, there is no study comparing anterior with posterior approaches. The main evidence for state-of-the-art treatment of C1-2 pannus is provided by retrospective case series.
Although such studies may not provide the most rigorous scientific data, they form the basis for the current approach to this condition. Inherent in the decision mak- ing process is a fundamental assumption regarding patients with pannus. Namely, patients with severe neurologic deficits have less potential for neurologic improve- ment with surgical intervention than patients with a less advanced condition.14 This assumption has not only been supported by the work of Ranawat and colleagues, but Reiter and Boden13 have shown that earlier surgical intervention in patients with milder myelopathy often leads to a more satisfactory outcome.
In terms of an algorithmic approach to this condition, the most agreed-upon indication for surgical intervention is the presence of a neurologic deficit in the set- ting of instability. Not only is such an indication the basis for any possible spinal surgery, but there are few other situations involving a degenerative spine in which conservative management has the potential for such drastic negative consequences.
For instance, the reported mortality for patients with cervical myelopathy from rheu- matoid arthritis at 1 year if left untreated can reach 50%, as shown by Kraus and co-workers.17 On the other hand, the treatment of asymptomatic patients with radio- graphically demonstrated instability has been controversial over the past several decades. However, with the more consistent use of MRI in such patients, most would agree that evidence of cord compression, even if asymptomatic, mandates surgery. Casey and associates18 argue that if the space available for the cord is less than 13 mm, a posterior cervical fusion should be considered. Such stabilization will prevent pannus progression, and in cases of a noncalcified mass, the pannus may regress over time.
In those patients with spinal cord compression, with or without neurologic defi- cit, many argue that reduction should be attempted.12 If reduction can be obtained with the use of cervical traction, then surgical methods can be used to accomplish stabilization in the reduced state.12 Alternatively, intraoperative reduction can be attempted using posterior cervical instrumentation without the use of traction.11 If reduction cannot be obtained, but posterior decompression is expected to provide adequate room for the spinal cord, a C1 laminectomy can be performed, followed by an occipitocervical fusion. If myelopathy worsens postoperatively after the use
of such techniques, persistent anterior compression at the cervicomedullary junction may require an anterior odontoid resection. However, initial anterior approaches should be considered at the outset in cases of severe anterior compression or cranial settling with basilar invagination that may not respond to traction and/or posterior stabilization alone. Based on their experience, Finn and co-workers1 contend that it is best to decompress the neural elements anteriorly at the outset in such patients.
They argue that it provides the best neural decompression and chance for neurologic recovery, and it may allow easier and more optimal atlantoaxial reduction before posterior fusion. This experience may be due in part to the fact that the pannus often prevents optimal posterior atlantoaxial reduction. Because of approach-related morbidity, however, most would argue that the transoral approach is indicated in patients with irreducible ventral compression at the cervicomedullary junction, as suggested in a retrospective study.19 In neurologically intact patients who do not meet the criteria stated earlier, conservative management may be considered, but careful follow-up must be maintained to detect new evidence of myelopathy.
The patient described in the Case Presentation underwent surgery based on two main considerations in this algorithm. First, she had decreased spinal canal diameter with distortion of the spinal cord. Second, she had mechanical pain unresponsive to conservative management. She was not placed in traction because in this case C1-2 did not show gross instability that required reduction. In addition, it was felt that the anterior compression did not require an anterior decompressive procedure both because of the absence of significant ventral compression on radiographs and because of the absence of myelopathy.
The Ranawat classification has been considered a simple but reliable tool for pre- dicting neurologic recovery after stabilization. Casey and colleagues18 showed that the majority of patients improve by at least one Ranawat class after surgical inter- vention. Patients with pure atlantoaxial instability also fare better than patients with basilar invagination. Finally, the prognosis has been shown to be poorer in patients with a subaxial canal diameter of less than 14 mm than in patients with a large canal diameter.12 Postoperatively, progression of myelopathy has been reported in 4% to 8% of cases in a retrospective study by Boden and co-workers.20 Potential causes of delayed worsening include the natural history of myelopathy in the setting of prior spinal cord damage, persistent compression, and nonunion, the latter of which can occur in up to 50% of cases involving a rheumatoid spine.16
The transoral approach is a well-established procedure for treatment of anterior compression at the craniovertebral junction, and it has gained great acceptance due in part to the work of Menezes and colleagues.21 Nonetheless, there is substan- tial potential morbidity associated with this approach, including the need for pro- longed tube feeding, the need for tracheostomy, soft palate and pharyngeal wound dehiscence, and CSF fistulas.19 Furthermore, following anterior decompression, the patient is often in overtly unstable condition until the posterior fusion is completed.
For this reason, patients must be firmly immobilized after anterior decompression until posterior fixation is accomplished. At a time when posterior stabilization of C1-2 was less safe and more cumbersome, Menezes and co-workers21 reported that roughly 75% of patients undergoing a transoral decompression required dorsal fixa- tion after odontoidectomy. According to a retrospective review by Menezes and Van Gilder,22 when osteoarthritis was present in the atlantoaxial joints, posterior fixation often was not required. However, given the efficiency and safety with which posterior instrumentation can be placed, and the likelihood that such arthritis would create pain for the patient, posterior stabilization after an anterior decompression is always recommended.
COMMENTARY
C1-2 instability can lead to pain and neurologic dysfunction from spinal cord or brainstem compression. For those patients with pain alone, conservative manage- ment should be considered. However, in the presence of persistent pain, pan- nus enlargement, or instability on dynamic imaging, posterior fixation should be
considered. In patients with spinal cord compression with or without neurologic dysfunction, surgery is indicated. If the compression is reducible, posterior fixation is the treatment of choice. If the compression is not reducible, two broad options exist: posterior decompression and posterior fusion, and anterior decompression and posterior fusion. As has been suggested earlier, the pannus may regress over time after posterior stabilization alone. However, this change may take months, and thus persistent anterior compression may require a subsequent anterior approach, such as a transoral approach. An anterior approach as the initial procedure may achieve a more optimal decompression of anterior lesions, but should only be car- ried out by surgeons experienced in this approach because of associated compli- cations. For this reason, the patient must also be clearly warned of the potential approach-related morbidity. However, in light of recent advancements such as the transcervical odontoidectomy, in which the C1-2 pannus may be resected via a more classic anterior cervical approach, anterior approaches to the craniovertebral junc- tion may carry less morbidity and thus may be used for severe pathologic conditions such as marked basilar invagination.
REFERENCES
1. Finn M, Fassett DR, Apfelbaum RI: Surgical treatment of nonrheumatoid atlantoaxial degenerative arthritis producing pain and myelopathy, Spine 32(26):3067–3073, 2007. This article describes the surgical experience of Dr. Apfelbaum, who is one of the most experienced surgeons in dealing with C1-2 pathology. In the article, the authors not only review their experience retrospectively, but also provide a working algorithm for dealing with nonrheumatoid atlantoaxial degenerative arthritis. It is a great read for both the beginner and the expert.
2. Kanavel AB: Bullet located between the atlas and the base of the skull: technique of removal through the mouth, Surg Clin Chicago 1:361–366, 1917.
3. Frempong-Boadu AK, Faunce WA, Fessler RG: Endoscopically assisted transoral-transpharyngeal approach to the craniovertebral junction, Neurosurgery 51(Suppl 5):S60–S66, 2002.
4. Wolinsky JP, Sciubba DM, Suk I, et al: Endoscopic image-guided odontoidectomy for decompression of basilar invagination via a standard anterior cervical approach. Technical note, J Neurosurg Spine 6(2):184–191, 2007.
5. Robinson RA, Southwick WO: Surgical approaches to the cervical spine, Instr Course Lect 17:299–330, 1960.
6. McGirt MJ, Attenello FJ, Sciubba DM, et al: Endoscopic transcervical odontoidectomy for pediatric basilar invagination and cranial settling. Report of 4 cases, J Neurosurg Pediatr 1(4):337–342, 2008.
7. Magerl F, Seemann P-S: Stable posterior fusion of the atlas and axis by transarticular screw fixation.
In Kehr P, Weidner A, editors: Cervical spine, Vienna, 1985, Springer-Verlag.
8. Harms J, Melcher RP: Posterior C1-C2 fusion with polyaxial screw and rod fixation, Spine 26(22):
2467–2471, 2001.
9. Sciubba DM, Noggle JC, Vellimana AK, et al: Radiographic and clinical evaluation of free-hand place- ment of C-2 pedicle screws. Clinical article, J Neurosurg Spine 11(1):15–22, 2009.
10. Sciubba DM, Noggle JC, Vellimana AK, et al: Laminar screw fixation of the axis, J Neurosurg Spine 8(4):327–334, 2008.
11. O’Brien JR, Gokaslan ZL, Riley LH 3rd, et al: Open reduction of C1-C2 subluxation with the use of C1 lateral mass and C2 translaminar screws, Neurosurgery 63(1 Suppl 1):ONS95–98; discussion, ONS98-99, 2008.
12. Nguyen HV, Ludwig SC, Silber J, et al: Rheumatoid arthritis of the cervical spine, Spine J 4(3):329–334, 2004.
13. Reiter MF, Boden SD: Inflammatory disorders of the cervical spine, Spine 23(24):2755–2766, 1998.
14. Ranawat CS, O’Leary P, Pellicci P, et al: Cervical spine fusion in rheumatoid arthritis, J Bone Joint Surg Am 61(7):1003–1010, 1979.
15. Riew KD, Hillibrand AS, Palumbo MA, et al: Diagnosing basilar invagination in the rheumatoid patient. The reliability of radiographic criteria, J Bone Joint Surg Am 83-A(2):194–200, 2001.
16. Papadopoulos SM, Dickman CA, Sonntag VK: Atlantoaxial stabilization in rheumatoid arthritis, J Neurosurg 74(1):1–7, 1991.
17. Kraus DR, Peppelman WC, Agarwal AK, et al: Incidence of subaxial subluxation in patients with generalized rheumatoid arthritis who have had previous occipital cervical fusions, Spine 16(Suppl 10):S486–S489, 1991.
18. Casey AT, Crockard HA, Stevens J: Vertical translocation. Part II. Outcomes after surgical treatment of rheumatoid cervical myelopathy, J Neurosurg 87(6):863–869, 1997. Dr. Crockard is one of the leading craniocervical surgeons in the world. In this article he and coauthors review his surgical outcomes for rheumatoid cervical myelopathy, underlining for the reader the outcomes that may be expected in this challenging group of patients..
19. Landeiro JA, Boechat S, Christoph Dhe H, et al: Transoral approach to the craniovertebral junction, Arq Neuropsiquiat 65(4B):1166–1171, 2007. This is a great technical review on the anatomic approach to the craniocervical junction. The transoral approach can be a daunting one even for the experienced spinal surgeon, and this article underlines some of the important aspects of the approach.
20. Boden SD, Dodge LD, Bohlman HH, et al: Rheumatoid arthritis of the cervical spine. A long-term analysis with predictors of paralysis and recovery, J Bone Joint Surg Am 75(9):1282–1297, 1993.
21. Menezes AH, VanGilder JC, Graf CJ, et al: Craniocervical abnormalities. A comprehensive surgical approach, J Neurosurg 53(4):444–455, 1980. Dr. Menezes is one of the most experienced craniocervi- cal surgeons and treats some of the most challenging pathologic conditions. This article underlines some of the ways in which he reviews and approaches such complex problems at the craniocervical junction.
22. Menezes AH, VanGilder JC: Transoral-transpharyngeal approach to the anterior craniocervical junc- tion. Ten-year experience with 72 patients, J Neurosurg 69(6):895–903, 1988. A follow-up article to the previous one by the same authors, this article specifically reviews the transoral approach to the craniocervical junction. Drawing on his vast clinical experience, Dr. Menezes sheds light upon the array of pathologic conditions that can be encountered at this area and describes his results.
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