9 The Spine



10.1055/b-0038-160359

9 The Spine

H. Boehm

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.

Fig. 9.1 Confirmation that vertebral arteries are present on both sides with a normal anatomical course to the basilar artery
Fig. 9.2 The skin incision is made from the occiput down to the spinous process of C3. The anesthetist is located at the foot end of the table on the right. This allows access to the head, neck, and upper body as well as to the posterior iliac crest for bone graft retrieval.
Fig. 9.3 Model of the exposed area: The ellipse indicates the exposed posterior craniocervical junction. Large convoluted veins (V) lie posterior to the root and can lead to significant blood loss.
Fig. 9.4 Determine the site for the stab incision that will be used for percutaneous insertion of the drill and screws. The landmarks for drill orientation in relation to the spinous processes can be more easily obtained by comparing the median sagittal scan to one that runs laterally through the joint. The red line indicates the desired entry points at skin and C2. Judge from the sagittal MRI whether cervical hyperlordosis or thoracic hyperkyphosis could hinder screw placement. An axial MRI calculated in the plane of the red line (“Magerl view”) indicates where the vertebral artery could be hit.
Fig. 9.5 (a) The drill sleeve for percutaneous placement of drill holes and insertion of screws along with the alignment block. The drill on the left side has already been inserted. On the right side, an awl marks the correct insertion point and secures the right side of the drill sleeve. (b) View from the left side: The percutaneous approach nearly halves the length of required spinal column exposure.
Fig. 9.6 Mini-open technique: the sleeve system for drill and screw insertion is pictured. At the top is shown a curved system that can be used when, for anatomical reasons, the optimal angle cannot be obtained with a straight sleeve.
Fig. 9.7 Placement of the graft-fixating suture around the posterior arch. Under constant bony contact a right-angled Overholt clamp is passed from cranial to caudal while protecting the dura at C1–C2. Then a nonresorbable no. 2 suture is grasped midway and pulled through, thus looping around the arch.
Fig. 9.8 The advantage of “Magerl trajectory imaging.” Imaging planes are chosen such that they correspond to the subsequent orientation of the screw. The ideal location for the drill is in slice 10. Upper right is the axial slice (prior to reduction). This permits a continuous bone channel for the screw through C2 and C1. The vertebral arteries can be seen in slices 9 and 12 and are located sufficiently far away. In this case, the anatomical conditions do allow insertion of drills and screws through a small main incision.
Fig. 9.9 (a,b) A ballpoint hook is used to determine the medial pedicle edge of C2. The entrance point on the C2 facet is opened with a small bur 2 to 3 mm laterally and as caudally as possible.
Fig. 9.10 –>(a–c) The awl from the inserted sleeve system in Fig. 9.5 is replaced with a drill. Under fluoroscopic imaging in the lateral view, a hole is drilled all the way into the C2–C1 joint (a). Then, by using the sublaminar thread in Fig. 9.7 and holding the C2 firmly, the atlas is repositioned relative to the axis and held in place while drilling is continued to the anterior cortex of C1. This is performed at a higher drill speed. In addition, care must be taken to ensure that the joint gap does not widen during drilling. After performing the same procedure on the other side, the reduction of C1 on C2 is retained temporarily. The first drill is then replaced with a screw, and after repeating this sequence on the other side definitive fixation is achieved. A washer should be used for osteoporotic bones. It is inserted through the incision (b) and then captured and fixated by the screw within the sleeve (c).
Fig. 9.11 Sequence for the insertion of drill and screws into C2 and C1. Left, the percutaneous drill sleeve has been inserted, and the entry point is enlarged with an awl. The awl is then replaced with the drill, and a second drill hole is placed. The first drill is replaced with a 2.7-mm screw, followed by the second screw through the second drill hole.
Fig. 9.12 Transoral release including atlas-preserving odontoid resection. (a) In the model: the red oval encircles the field of view, which is held open with a Crockard spreader. (b) Patient with mouth and uvula retractor after sterile draping.
Fig. 9.13 (a) View of the posterior pharynx wall from the patient’s right side. The uvula retractor is visible on the left edge of the picture. A midline incision through mucosa and muscularis is visible. (b) The left joint is exposed (J). AA denotes the left side of the arch of the atlas. (c) The base of the odontoid (O) is exposed. The atlantodental joint cartilage emerges cranial to the base.
Fig. 9.14 Osteotomy of the odontoid. (a) First, a K-wire with a threaded tip (see the arrow in the schematic) is inserted into the odontoid as far cranial as the preserved arch of C1 allows. (b) Next, a burr and Kerrison are used to make a 5-mm transverse osteotomy at the base of the odontoid. (c) Osteotomy gap (blue on the model) after complete detachment of the odontoid.
Fig. 9.15 Mobilization and removal of the odontoid. (a) The odontoid (O) is pulled down over the fixation wire by deflecting it with a chisel (the arrow on the model). This maneuver partially closes the osteotomy. (b) The odontoid is then caudalized as far as possible, thus closing the osteotomy. Next, the insertion site for a second fixation wire is burred open as far cranial as possible. (c) The caudal wire has been removed and the odontoid, held by the second K-wire, is shortened caudally with a 5-mm Kerrison and pulled caudally using the maneuver in (a) until the osteotomy is closed again. Finally, the remaining cranial part (yellow on the model) of the odontoid is now completely mobile and can be taken out in the next step.
Fig. 9.16 The odontoid has been removed. (a) In the retrodental tissue mass a partially preserved transverse ligament (tr; yellow on the model) can be identified. (b) The fully decompressed, uninjured dura (Du; blue on the model). (c) The posterior pharyngeal wall wound (red area in model) is closed with deep sutures.

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May 21, 2020 | Posted by in RHEUMATOLOGY | Comments Off on 9 The Spine
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