Atlantoaxial arthritis is not as common as arthritis of the subaxial spine, but when it occurs, it can be associated with severe pain and myelopathy. Most commonly occurring in the setting of rheumatoid arthritis, a pannus of the C1-2 joint can also result from atlantoaxial osteoarthritis or healing following trauma to the C1-2 junction. When degenerative in nature, the pannus has also been termed pseudotumor or articular, ganglion, synovial, or juxtafacet cyst. The classic presentation is mechanical suboccipital pain and/or myelopathy from ventral spinal cord compression at the craniocervical junction.
The diagnosis of C1-2 pseudotumor is best made based on a thorough medical history in combination with the findings of various imaging modalities. Magnetic resonance imaging (MRI) is ideal for evaluation of spinal cord pathology and is thus essential in the workup to determine the location and severity of spinal cord or brainstem compression. In conjunction, computed tomography (CT) is used to evaluate at least three important aspects of the bony anatomy. First, the degree of bony erosion must be assessed to determine the extent of atlantodental arthritis and lateral mass arthritis. This is especially relevant when basilar invagination has occurred secondary to cranial settling and “pistoning” of the dens upward as the C1-2 joint subluxes and rotates. Second, the pannus should be evaluated for calcification to provide a sense of overall rigidity of the mass. Third, if surgery is to be planned, bony anatomy must be clarified for purposes of both decompression and instrumentation. A final important imaging modality is flexion-extension radiography to determine motion and thus instability at the C1-2 joint. Classically, motion is examined most closely by assessing the atlantodental interval; however, in the setting of a previous trauma, motion at the base of the odontoid should also be examined. Unfortunately, differentiating a degenerative pannus or rheumatoid pannus from older healing C2 fractures, calcium pyrophosphate deposition, metastatic lesions, primary bone tumors (chordomas), primary cartilaginous tumors (chondromas, chondrosarcomas), or meningiomas can be difficult using imaging studies alone.
Surgical decompression is the definitive treatment for a degenerative pannus leading to myelopathy. Historically, transoral decompression combined with posterior stabilization has been most commonly used. However, posterior-only approaches have been used to avoid the morbidity associated with the transoral route. In such cases, the hope is that progression of myelopathy can be halted with stabilization, and in cases of a noncalcified pannus, the mass may resolve following the procedure. The controversy regarding which approach is preferable is the subject of this chapter. A case of a C1-2 pannus is first presented. Surgical options are then discussed, and a literature review is provided to support the best approach.
A 77-year-old woman came for treatment of neck pain after experiencing a series of falls over the previous 2 years. After the falls she did not initially seek treatment for the neck pain. However, the neck pain became progressively severe. In addition, she began to complain of increased clumsiness of gait. She went to her primary care physician, who ordered an MRI scan and sent her for neurosurgical consultation.
Exam: The patient reported no problems with fine motor movement of her hands, and no bowel or bladder symptoms. She also did not complain of any cranial nerve dysfunction (difficulty swallowing, coughing, gagging, impaired lingual articulation, etc.) or of the Lhermitte phenomenon. She also had no history of rheumatoid arthritis. On physical examination, the patient’s neck was supple, and she did not guard against movements in any degrees of motion. Her strength was 5/5 in all muscle groups of the upper and lower extremities. She had an antalgic gait that she attributed to long-standing left hip arthritis, but otherwise showed no ataxia or spasticity in walking. Reflexes were 1+ throughout. She had no Hoffman sign, Babinski reflex, or clonus. Sensation was grossly intact to light touch and pinprick.
Imaging: An MRI scan of the cervical spine revealed a pannus at the C1-2 joint leading to some distortion of the anterior thecal sac ( Figure 10-1 ). No signal change was present in the spinal cord or lower brainstem. CT images of the cervical spine revealed the presence of an old type II odontoid fracture, anterior tubercle of C1 fracture, and calcified pannus around the C1-2 joint ( Figure 10-2 ). Flexion-extension radiographs were taken, but did not show any gross movement of the odontoid process or change in the atlantodental interval ( Figure 10-3 ).
Surgical Options and Fundamental Techniques
Transoral-Transpharyngeal Decompression Plus Posterior Stabilization
In cases demonstrating clear anterior spinal cord compression that is irreducible, direct ventral decompression of the spinal cord is indicated. This approach provides access to the lower clivus, foramen magnum, anterior arch of C1, underlying odontoid process of C2, and down to the C3 vertebral body in some patients. Since first described in 1917 by Kanavel, transoral approaches have been used extensively to address a wide range of pathologic entities.
Contraindications to this approach include surgeon unfamiliarity with the procedure, limited patient mouth opening, and extensive pathology that extends beyond the access of a standard transoral approach (e.g., large tumors, basilar invagination). Such situations may warrant extended transoral approaches involving maxillary or mandibular osteotomies.
The technique involves supine positioning followed by orotracheal intubation. Initial direct palpation of the posterior oropharynx allows identification of the anterior arch of C1 and the body of C2. The oral cavity is cleansed with chlorhexidine gluconate oral solution, intravenous antibiotics are provided, and the face is draped to allow access to the mouth and the nasal cavity. A self-retaining oral retractor (classically a Crockard retractor) is placed over the teeth and expanded to keep the mouth open. Self-retaining retractors are then attached to the retractor to keep the tongue depressed. If required for improved visualization, the soft palate can be divided in its midline. To avoid postoperative swallowing and phonation problems that may arise after palatal splitting, some authors suggest securing the uvula to a red rubber catheter that can be placed through the nares and out the pharynx and secured to retract the soft palate.
The posterior pharyngeal mucosa is infiltrated with local anesthetic and epinephrine, and a midline posterior incision is made from the clivus to the upper border of the third cervical vertebra ( Tips from the Masters 10-1 ). The pharyngeal mucosa, pharyngeal constrictor musculature, and longus colli and longus capitis musculature are then elevated as a single myomucosal flap from the underlying anterior longitudinal ligament. Resection of the pannus is done piecemeal with curettes, rongeurs, and high-speed drilling. Some surgeons advocate maintaining the C1 anterior arch and pulling the resected odontoid and pannus tissue out from underneath it ( Tips from the Masters 10-2 ). This maneuver maintains the integrity of the C1 ring. Access to the pannus may be challenging, however, and thus resection of the anterior C1 ring may be required. Resection of the hypertrophied tectorial membrane is also often required to truly decompress the dura. Unfortunately, this maneuver may be associated with a cerebrospinal fluid (CSF) leak, and the anterior dura may be exceptionally difficult to repair primarily. Dural graft onlays may be used with fibrin glues in conjunction with a lumbar drain to help with healing.
Unipolar cautery should be used carefully laterally, because the carotid arteries are close as they enter the skull base.
Removing the anterior C1 arch and removing the odontoid from the top down is suggested. This will avoid a “floating” odontoid process, which may be difficult to secure and remove.
Watertight closure of the posterior pharynx should be attempted in all cases, especially if CSF is encountered. It should be closed in two layers (pharyngeal musculature and pharyngeal mucosa), and the soft palate (if sectioned) should then be carefully approximated in three layers (nasal mucosa, muscularis, and oral mucosa), all with interrupted absorbable sutures. Postoperative stabilization is carried out as soon as possible.
More recent modifications of the standard transoral approach include use of image guidance via stereotactic navigation, intraoperative MRI, and endoscopy to improve the view without performing additional osteotomies. Specifically, the ability to visualize the lower and middle clivus is limited with the transoral approach, and full soft palate splitting, hard palate splitting, or extended maxillotomy procedures may be required. Such procedures may lengthen operating time, prolong recovery, and increase patient morbidity, and a 30-degree endoscope may be used to avoid these additional procedures.
Transcervical Decompression Plus Posterior Stabilization (Transcervical Endoscopic Odontoidectomy)
In an attempt to limit the approach-related morbidity of the transoral route (infection from oral flora, meningitis, need for oral rest for pharyngeal healing, etc.), Wolinsky and colleagues developed a minimally invasive method of performing an odontoidectomy via a standard anterior cervical approach. Based on a traditional Smith-Robinson anterior cervical approach, the surgical corridor follows the trajectory of a transodontoid screw, which allows exposure from the midcervical spine (C4) to the inferior clivus. In this way, the approach and anatomy are familiar to spine surgeons, and the oral cavity is completely isolated from the surgical field. However, surgery must be done via a tubular retractor, and thus navigation and endoscopy are recommended ( Tips from the Masters 10-3 ). In addition, as with transodontoid screw placement, an ideal trajectory may not be achieved in patients who are obese, barrel-chested, or severely kyphotic.
Visualization is key because drilling of the odontoid is being done down a narrower tube. Thus, the endoscope should be rigidly fixed and routinely cleaned.
The technique involves supine positioning of the patient with the head fixed to the bed via a halo or Mayfield clamp. Using isocentric fluoroscopy, a CT-like image is acquired, which allows registration of preoperative images with the current position in the operating room. A standard Smith-Robinson approach to the cervical spine is then pereformed. Blunt dissection along the anterior spine proceeds rostrally until the anterior tubercle of C1 is identified. A beveled tubular retractor is then inserted and rigidly secured to the bed so that it is docked in the midline, with the rostral tip of the retractor on the C1 tubercle and the caudal aspect over the C2-3 disk. A 30-degree endoscope is then placed down the retractor so that the endoscope lies in the superior aspect of the retractor field. At this point, endoscopic visualization of anatomic landmarks is correlated with the frameless stereotactic system ( Tips from the Masters 10-4 ).
Confirmation of anatomy should be done routinely, ideally with intraoperative CT or isocentric C-arms, to actively assess the amount of bony compression remaining.
Described by Wolinsky and colleagues for the treatment of basilar invagination, this technique provides good radiographic and neurologic results in both adults and children ( Figure 10-4 ). Following such decompression, the incision is closed in a standard, multilayered fashion as would be done for a Smith-Robinson cervical exposure. The halo ring is secured to the halo vest with the neck now placed in a neutral position, and the patient is repositioned for a posterior cervical or occipital cervical fusion. Postoperatively, the patient is left intubated overnight. After extubation, the patient can resume oral intake.
Posterior Fixation Alone
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 mentioning 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 following 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 ). 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 Melcher described the placement 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.