C1-C2 Fusion (Posterior Screw Fixation)

4 C1-C2 Fusion (Posterior Screw Fixation)

Dieter Grob

Goal of Surgical Treatment

To stabilize and fuse the atlantoaxial segment in its anatomic position.

Diagnosis

Suboccipital pain, headache, and neckache are nonspecific symptoms of painful changes in the atlantoaxial segment. Neurologic deficit is rarely observed. Functional clinical investigation includes rotation of the head in a maximally flexed position. In this position, the facets of the lower cervical spine are blocked against rotation and the remaining rotational motion must be executed at the atlantoaxial segment.

The diagnosis is often made by normal radiographs. An anteroposterior open-mouth view reveals changes of the facets and the lateral masses of the atlas and axis. Lateral view and flexion extension radiographs provide information about the relationship between the occiput, atlas, and axis, and demonstrate any instability in the transverse plane. More detailed information about bone resorption, size of the pedicles of the axis, and soft tissue involvement are gained from computed tomography (CT) and magnetic resonance imaging.

Indications for Surgery

1. Normal atlantoaxial anatomy confirmed in CT scan

2. Nontraumatic (ligamentous) instability of the atlantoaxial segment (Figs. 4–1 and 4–2)

3. Traumatic instability including fractures of the atlas and axis and ligamentous injuries

4. Degenerative changes of C1-C2

5. C1-C2 instability due to loss of bone (tumor, infection)

Contraindications

1. Missing pedicles of the axis

2. Congenital malformations (ill-defined anatomy)

Advantages

1. High fusion rates.

2. Translational and rotational displacement in the C1-C2 segment effectively blocked.

3. Immediate postoperative stability: soft collar sufficient for postoperative management.

Disadvantages

1. Potential risk of injury to the vertebral artery and medulla

2. Technically demanding

Procedure

Positioning

Positioning of the patient is crucial for correctly inserting the screws. Surgery is performed with the patient in the prone position. Preferably, the head is separately fixed in a device (halo, Mayfield) that allows unconstrained positioning. Basically, the subaxial cervical spine is axially extended and the atlanto-occipital joint flexed. To achieve this position, the pivot should come to rest approximately at the level of the external meatus. The posterior iliac crest is prepared for graft harvesting.

Note:

1. The eyes are taped closed so that they will not be exposed to antiseptic prepping.

2. Draping and positioning have to take into account the possibility of intraoperative use of the C-arm in the lateral position.

Exposure

The skin incision is made strictly in the midline from the occiput to the mid-cervical spine. The nuchal fascia and the superficial muscles are divided. By this standard midline approach, the spinous process of the axis is identified and this serves as a landmark. Exposure of the midline of the atlas and the C2-C3 facets delineates the operative field. Subperiosteal dissection, following the border of the spinal canal along the superior aspect of the lamina, leads to the isthmus of the axis. This structure represents the key to anatomic orientation for screw insertion (Fig. 4–3).

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