Surgical Approach

The patient is positioned in the prone position, and the position of C1–C2 is checked using lateral image intensifier control. The alignment of C1–C2 is facilitated by traction either with Gardner-Wells tongs/halo or a Mayfield clamp, the latter of which controls translation more easily. The neck is flexed as much as possible to facilitate insertion of the screws, and an image intensifier is used to exclude redislocation in case of a fracture dislocation ( Fig. 11.1 ).

A midline incision is performed from the occiput to the tip of the spinous process of C3. The arch of C1, spinous process, laminae, and inferior articular processes of C2 are exposed subperiosteally. In case of a persistent anterior dislocation of C1 over C2, a reduction is done by pushing on the spinous process of C2 and/or by pulling gently on the posterior arch of C1, either with a towel clamp or with a sublaminar wire or suture sling. Persistent posterior dislocation would require opposing forces.

It is recommended that the surgeon gently expose the inner side of the isthmus and pedicle of C2 and stay medially as close as possible to this landmark. A small dissector is used to expose the cranial surface of the lamina and isthmus of C2 by careful subperiosteal dissection up to the posterior capsule of the atlantoaxial joint ( Fig. 11.2a ). Medial to the isthmus, the atlantoaxial membrane is visible. The laterally situated vertebral artery is not exposed. It is further recommended to get a computed tomography (CT) scan of the C1–C2 segment before a surgical intervention to rule out an anomalous course of the vertebral artery.

Standard Technique

Using lateral image intensifier control, a 2.5-mm-long drill bit is inserted in a strictly sagittal direction. The oscillating attachment prevents soft tissues from being wrapped around the drill bit. The entry point of the drill bit is at the lower edge of the caudal articular process of C2 ( Fig. 11.2b ). The drill bit goes through the isthmus near its posterior and medial surface. It then enters the lateral mass of the atlas close to its posteroinferior edge. Anteriorly, the drill perforates the cortex of the lateral mass of C1. The screw length is measured, and the direction of the screw canal is checked using an image intensifier ( Fig. 11.2c ).

The 3.5-mm cortex screws are inserted after checking with a 3.5-mm tap across the C1–C2 joint; the anterior cortex of C1 must not be tapped ( Fig. 11.2d ). Proper caudocephalad drilling may be difficult because the neck muscles and the upper torso prevent the correct placement of the drill bit. Gently pulling the spinous process of C2 cranially with a towel clamp facilitates drilling. It is often necessary to drill through a distal percutaneous stab wound to place the drill in the correct angle of ~60°. Prepping and draping of the upper thoracic spine are necessary to be able to enter the drill bit through a stab incision.23–25

Drilling in a horizontal direction must be avoided because

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  At the level of C2, the vertebral artery runs upward anteriorly to the C1–C2 joint and could easily be damaged.

  
  
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  The screw could exit C2 anteriorly and not enter the atlas.

Cannulated Screw Technique

As in direct anterior fixation of the odontoid,26 we used the cannulated screw technique for both posterior and anterior transarticular screw fixation.7,10 This technique also has been used and published by others.26,27 With Kirschner (K) wires as drill guides, we performed the surgery in a minimally invasive manner. Through bilateral stab wounds, a K wire can be placed under anteroposterior and lateral simultaneous image intensifiers from the described entry points toward the lateral projection of the C1 arch. The interspinous graft can then be placed between the C1 and C2 through a small midline incision. This technique has been further elaborated by the Ulm group.23–25 More recently, an image-guided technique was presented; however, this technique is far from being used on a routine basis.28

Using lateral image intensifier control, a 1.2-mm K wire is inserted with a surgical drill guide in a strictly sagittal direction into each hole ( Fig. 11.3a, b ). The entry point of the K wire is at the lower edge of the caudal articular process of C2 ( Fig. 11.3a ). The length of the screw is established with a special ruler by measuring the protruding part of the guide-wire ( Fig. 11.3c ). Before inserting the cannulated screw over the K wire, the entrance for the screw is prepared by a special 3.5-mm cannulated countersink ( Fig. 11.3d ) to facilitate the starting purchase of the screw. The appropriate 3.5-mm self-tapping, cannulated cancellous bone screw (same as for odontoid fixation, usually ~40–45 mm long) is inserted over the guidewire ( Fig. 11.3e ). The progress of the screw must be observed under lateral image intensifier control to ensure that the K wire does not migrate proximally beyond the C1 arch and the screw does not push away (anteriorly and upward) the lateral mass of C1, consequently dilating the C1–C2 joint.

In severe degenerative diseases, the sclerotic subcortical bone of the C2 joint may prevent insertion of the self-drilling screw. In this case, a 2.7-mm cannulated drill bit is used to cross the joint, and a cannulated fully threaded 3.5-mm screw can be inserted after regular tapping of the predrilled screw hole.

Fusion

Following bilateral screw fixation, according to the above described techniques, a posterior C1–C2 fusion is performed, preferentially Brooks-Jenkins or Gallie fusion.5,6 According to Magerl’s technique, it is preferable to supplement the graft with a posterior wire or cable, as this increases the stability of the fixation and hence the fusion rate ( Fig. 11.3f, g ). Instead of a wire, a nonresorbable suture can be used.

When there is a defect or fracture of the posterior arch of C1, a fusion of the atlantoaxial joint must be performed. For visualization of the atlantoaxial joint, K wires are drilled into the posterior aspect of the lateral mass of the atlas. For this purpose, the greater occipital nerve is retracted cranially. The soft tissues containing the greater occipital nerve and its accompanying venous plexus are retracted simultaneously. The atlantoaxial joints are exposed by opening the posterior capsule, thus making the C1–C2 joint visible ( Fig. 11.4 ). The articular cartilage of the posterior half of the facet joint is removed with either a small chisel or a sharp curet, after which the joints are packed with cancellous bone, and the screws are inserted.

Advantages and Disadvantages

The advantages of transarticular C1–C2 screw fixation are biomechanical superiority to the wiring techniques, the possibility of maintaining reduction, and the lack of need of integrity of the posterior arch of C1 for the fixation technique. Furthermore, this technique can be easily combined with a Gallie fusion, thus obviating the need for relevant external immobilization.

The disadvantages include the fact that this is a demanding technique and that there is a potential risk of bleeding due to injury to the venous plexus located lateral to the entry point of the screws or due to injury of the vertebral artery.29–33 This is particularly true in anomalies of the vertebral artery course in relation to the massa lateralis of C1 and C2.34–36 An aiming device may facilitate insertion of the screws.37,38 It may be difficult to apply this technique in patients with an upper thoracic kyphosis because the necessary inclination of the screws may be in conflict with the kyphosis, and the insertion of the screw therefore may be limited.

Depending on the obliquity of the screw insertion, a complete reduction of the C1–C2 joint may be necessary. When there is erosion of the transverse process of C2, the vertebral artery may change direction; this aberrant trajectory of the vertebral artery may make this technique impossible. In such a case, bilateral transarticular screw fixation may not be possible. An option may be unilateral transarticular screw fixation combined with posterior C1–C2 wiring.

Case Illustration

Transarticular screw fixation of C1–C2 with Gallie-type titanium cable fixation in a 55-year-old rheumatoid patient is shown in Fig. 11.5.

Related posts:

9 Congenital and Developmental Anomalies of the Craniovertebral Junction 16 Transoral Surgery 12 Occipitocervical Stabilization 20 Intraoperative Neurophysiological Monitoring in Surgery for the Craniovertebral Junction 19 Image-guided Surgery in the Craniovertebral Junction and Upper Cervical Spine 22 Techniques of Occipitocervical Fixation

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