9.1 Cervical Spine: Atlantoaxial Reduction and Fusion

Indication

Atlantoaxial instability >5 mm. Significant retrodental pannus formation. Onset of cranial settling.

Differential therapeutic considerations

Is there a preexisting fixed dislocation and/or significant cranial settling that requires a transoral odontoid resection and release before the spondylodesis procedure? Is there any pertinent segmental instability that could affect intubation?

Anesthesia specifics

Metal-reinforced endotracheal tube. Videolaryngoscopic or fiberoptic intubation. Anesthetic agents must be limited to those that allow for intraoperative neuromonitoring. Anesthetist and anesthesia equipment are positioned at the foot of the patient.

Specific disclosures for patient consent

Risk of vertebral artery injury resulting in:

• 
  

  Ischemic damage in the vascular territory of the basilar artery.

  
  
• 
  

  Significant blood loss.

Proximal spinal cord injury. Occipital nerve injury/neuralgia. Implant malposition with dural injury. Risk of pseudarthrosis and subsequent implant failure.

Instruments

Basic dorsal cervical spine pan:

• 
  

  Open approach: C1–C2 transarticular screw fixation instruments, 2.7-mm or 3.2-mm diameter screws with a length of 38 to 48 mm.

  
  
• 
  

  Mini-open technique: sleeve guide system for percutaneous placement of screws using Magerl’s technique.

  
  
• 
  

  As a modification for either of the above, if standard straight instruments cannot be used for a severe high thoracic kyphosis, curved drill sleeves (see Fig. 9‑6 ) are needed.

  
  
• 
  

  The Harms/Melcher cervical polyaxial screw-rod fixation system (see below) may be needed for C1 and C2 stabilization. An occipital plate is also required if there is advanced C1 destruction.

If a transoral release is necessary, the Crockard or Harms transoral instrument set will be required. Radiographic image intensifier. Intraoperative neuromonitoring. Intraoperative computer-assisted navigation may be needed.

Preoperative considerations/specific diagnostic investigation

Assessment of the C1 joints: are they still large enough? If not, C0–C2 fusion using an occipital plate/rod system is indicated.

The extent of thoracic kyphosis and deflectability of the subaxial cervical spine determine whether the orientation for the transarticular drilling and screw placement can be achieved.

Are vertebral arteries present on both sides and is their caliber sufficient?

Is there any alteration in the spatial relationship between axis or atlas and the vertebral arteries as they exit C2 and enter the foramen magnum (Fig. 9‑1 )? If so, are the vessels at risk of injury after repositioning or during drilling and screw placement?

Is intraoperative spinal cord monitoring necessary?

If functional imaging of the head demonstrates inadequate reducibility in extension, the need for transoral joint mobilization and/or odontoid resection as a preceding step should be determined preoperatively. Usually, however, intraoperative reducibility is significantly greater than that indicated by the preoperative functional imaging.

Position

Prone position on a spine frame. Operating table with adjustable head section. Head positioning device, possibly with a mirror that allows for intraoperative assessment of position-related pressure points on the eyes and nose (prone view). The table should be tiltable head up/feet down to reduce blood loss. However, this position requires a mechanism to prevent the patient from shifting caudally.

Sterile draping that allows:

• 
  

  Radiolucent imaging in two planes.

  
  
• 
  

  Intraoperative adjustability of the headrest for reduction.

  
  
• 
  

  Access to the posterior iliac crest for extraction of a corticocancellous graft.

Key steps

If reducibility is questionable

Following induction of anesthesia under full muscle relaxation and in supine position, place a strong support underneath the spinous processes from C2 to C7 and apply pressure through the mouth on the anterior arch of C1 under the guidance of lateral fluoroscopy imaging. If not adequately reducible, an additional transoral release should be performed before the posterior fixation/fusion, in order to allow reduction (see below).

Bone graft harvesting

It is preferable as the first step to obtain a corticocancellous graft from the posterior iliac crest: A 3-cm-long skin incision is made just lateral to the posterior spine of the iliac crest, and a 15 × 25 × 6 mm corticocancellous wedge is extracted from the outer table. By maintaining meticulous control of the osteotome, the posterior iliac crest and its stability can always be preserved, and injury to the iliosacral joint avoided. Additionally, using a curet, a few cancellous bone chips should be taken, which can later be packed laterally underneath the structural graft. To minimize postoperative blood loss, bleeding bone surfaces are carefully covered with a collagen fleece.

Approach

If the open technique is used for transarticular screw fixation of C2/C1, the skin incision must be extended down to the level of the T1 spinous process, and the posterior neck musculature must be deflected down to C6 in order to accommodate the implantation angle. In addition to the tissue trauma of the approach, this increases the risk of secondary muscle dehiscence and impaired wound healing. Intraoperative orientation, accuracy of drilling, and screw placement are slightly more difficult if it is carried out using our mini-open technique. Because drilling and screw implantation are performed percutaneously through drill sleeves inserted into two high thoracic stab incisions, our procedure minimizes the posterior exposure to the area of C1 and C2. The technique is described below.

Surgical technique for atlantoaxial reduction and fusion

Make a midline incision 4-cm in length from the occiput to the spinous process of C2, see Fig. 9‑2.

Perform subperiosteal exposure of the C2 spinous process and continue dissecting laterally toward the lamina and the C2–C3 intervertebral joint. This is best accomplished using a Cobb elevator. Countertraction is necessary if there is significant preexisting translational and rotational instability. After palpation of the arch of C1, an additional 15 mm on each side of the midline is exposed subperiosteally. The area cranial to the arch of the atlas should not be exposed further laterally due to its proximity to the vertebral artery. Venous plexuses run in the lateral portion of the C1–C2 interlaminar space (V in Fig. 9‑3 ) and have a tendency to bleed heavily. As a rule, hemorrhage can be prevented by bluntly separating the soft tissues and pushing them to the side with a small cotton swab.

After determining the insertion point, make an 8-mm stab incision (Fig. 9‑4 ). Introduce the coupled drill sleeve, initially fitted with an awl. Verify the direction and the correct entry point, first in a lateral radiographic view and then in AP. Under fluoroscopic imaging, drill through C2 into the joint space of C2/C1, which usually can be felt. Verify the reduction and continue drilling through C1, aiming at the middle third of the anterior arch under lateral radiographic control. A drill sleeve guide (Fig. 9‑5 ) is useful for this step. Determine the correct screw length. Replace the second drill and inner bushing with a screwdriver and attached screw. Insert a washer into the exposed site and capture it with the tip of a screw that has been inserted through the guide sleeve. Turn the screw under fluoroscopic imaging while maintaining direct visualization of the insertion site and carefully watching for inadvertent C1–C2 joint distraction.

If a sufficiently small angle cannot be maintained due to a high thoracic kyphosis, one solution might be to use the curved drill sleeve system (shown in Fig. 9‑6 ) instead of the straight sleeve.

Following reduction, the goal is to achieve a bony bridge between the C1 and C2 laminae. This is optimally achieved by bridging with a U-shaped corticocancellous iliac graft that is affixed to the arches of C1 and C2 and the spinous process of C2. The Magerl screw technique generally ensures adequate primary stability of the construct. It is therefore normally sufficient to secure the graft with a nonresorbable no. 2 suture using the Gallie technique, a cost-effective and MRI-compatible solution.

In addition, hypertrophy of the ligamentum flavum may lead to a stenosis between the atlas and axis. To avoid any risk of postoperative stenosis and in order to have optimal visual control during sublaminar placement of the thread, the dura should be dissected free several millimeters on each side of the midline.

The ligaments connecting the occiput and atlas, however, should be weakened as little as possible. Remove a 3-mm-wide section of the atlanto-occipital ligament. This will provide sufficient space to pull the suture through or, if necessary, to perform a more stable fixation with a cable or wire equivalent. We prefer to use a modified Overholt clamp for passing the thread around the posterior arch of the atlas (Fig. 9‑7 ). The doubled suture is looped around the arch of C1 and can be used for maneuvers of reduction and for temporary fixation to the C2 spinous process during drilling.

Correct placement of the drill hole is crucial for stable and safe screw fixation (see also Fig. 9‑8 ).

Magerl developed a very efficient technique to determine the mediolateral insertion point by palpating the medial pedicle edge and entering 2 to 3mm lateral to it. The other coordinate for placement of the screw lies on the C2 joint facet just cranial to its capsular insertion point. See Fig. 9‑9, Fig. 9‑10, Fig. 9‑11.

Surgical technique for transoral joint release and/or odontoid resection when atlantoaxial subluxation is no longer reducible

If an attempt at manual realignment under general anesthesia (see above) demonstrates that the subluxation is not adequately reducible, the patient is kept in the supine position and transoral mobilization is carried out prior to posterior stabilization. It is usually insufficient to simply mobilize the atlantoaxial joints because of reactive changes at the atlantodental joint. Therefore, the necessity of an odontoid resection should be included in the preoperative planning and when taking the patient’s consent.

To make a monosegmental procedure possible, the anterior arch of the atlas must be preserved. Our own technique is outlined below.

It is best to perform the transoral portion under visualization with an operating microscope, with the surgeon sitting at the patient’s head. Following orotracheal intubation, the nasopharyngeal cavity is disinfected with betadine solution (see Fig. 9‑12 ).

After insertion of a mouth and uvula retractor the anterior tubercle of the atlas is easily palpable, even in rheumatoid patients, and serves as a landmark throughout the procedure. The approach is through a midline incision from the base of C2 up to 1 cm cranial to the anterior tubercle. An adequate exposure and secure wound closure are obtained by sharply detaching the capitus longus muscle transversely from the caudal edge of the arch of the atlas and pushing both the muscle and its mucosa laterally.

Dissecting laterally along the caudal arch of the atlas leads to the C1–C2/C2 joint even in cases of subluxation (Fig. 9‑13 b). After verifying the position of the vertebral artery, the joint is cleaned out on both sides, and reduction is attempted using an elevator. If this is sufficient, the joint cartilage is completely removed, and the incision is closed. If the correction is inadequate and there is a possibility of (or preoperative diagnostic investigation shows) a substantial retrodental mass, the procedure is expanded to include an odontoid resection (Fig. 9‑14, Fig. 9‑15 ).

The principle of an atlas-sparing odontoid resection consists of making a 5-mm-wide transverse osteotomy on the base of the odontoid and pulling the odontoid peg caudally in a stepwise fashion utilizing a threaded K-wire (Fig. 9‑15 a).

As soon as the defect of the osteotomy has been closed by this maneuver, a second K-wire is inserted cranial to the first (Fig. 9‑15 b) and the caudal end of the odontoid is shortened another 5 mm. This step may need to be repeated until the remainder of the odontoid is free and can be removed (Fig. 9‑15 c). Rarely, the apical odontoid ligament, if still present (uncommon in rheumatoid patients), may need to be cut.

Finally, remove the retrodental granulation tissue. It is not uncommon to find solid masses that have formed from long-standing cysts that have filled with fibrin over time. Caveat: The walls of those cysts can be densely adherent to the dura. See also Fig. 9‑16.

In the last step the detached parts of the longus colli muscle are folded back and reattached. The posterior pharyngeal wall is closed with embedded full-thickness interrupted stitches. The surgeon places a gastric tube through the mouth prior to turning the patient prone for posterior screw fixation and spondylodesis.

Specific complications

Implant malposition. Injury to the dura. Pseudarthrosis with secondary implant breakage. Distraction of the C1–C2 joint space

Postoperative aftercare

Neck brace for 8 to 12 weeks, depending upon bone quality. Isometric exercises. Patient-driven exercises of the neck muscles against resistance.

In the event of an additional transoral procedure, give parenteral nutrition and antibiotic coverage for the first 5 days; daily antiseptic mouth rinses.