Transarticular Screws for C1-2 Fixation

Indications

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Indications for C1-2 transarticular screw fixation are atlantoaxial instability, rheumatoid arthritis, congenital abnormalities, os odontoideum, tumor, and ligamentous abnormality. Trauma and rheumatoid arthritis are the two most common indications for C1-2 fixation.
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C1-2 transarticular screws can also be used in patients with atlantoaxial instability who have failed external orthosis treatment (including halo vest) and patients who develop pseudarthrosis after undergoing C1-2 fixation and fusion with other techniques such as wiring.
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Biomechanical studies in cadavers showed that C1-2 transarticular screws provide slightly better fixation than C1–lateral mass/C2 pars screws in case of rotary subluxation.

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The anatomic relationship between the C2 foramen transversarium and the C1-2 facet joint must be studied carefully preoperatively because 18% to 23% of patients have a high-riding foramen transversarium (and vertebral artery) on at least one side that would prevent safe placement of a C1-2 transarticular screw. Thin-cut CT scans of the cervical spine with sagittal reconstruction generally offer sufficient detail to analyze the course of the vertebral artery C2.
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The procedure is relatively contraindicated in polytrauma patients with severe injury to other organ systems, elderly patients with other significant comorbidities, and patients who may be unable to tolerate a prone procedure.

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In patients with severe canal stenosis and significant myelopathy, care must be taken to minimize flexion of the neck during intubation. Awake intubation with fiberoptic assistance should be considered in cases of difficult airway or extremely unstable spines.
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Neuromonitoring with motor evoked potentials (MEPs) or somatosensory evoked potentials (SSEPs) should be used in patients with severe myelopathy. Prepositioning baseline MEPs or SSEPs should be obtained from patients before putting the patient in the prone position to ensure positioning has not compromised the spinal cord. Anesthetic agents should be adjusted for neuromonitoring purposes in these cases.
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In cases of spinal cord injury or severe myelopathy, maintenance of blood pressure in the normotensive or slightly hypertensive (mean arterial pressure > 90 mm Hg) range may be crucial to optimize perfusion of the cord.

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The head is positioned in a neutral position. Extreme care is taken to avoid forward translation and flexion of the spine, which can cause worsening spinal cord compression. Postpositioning MEPs or SSEPs are immediately checked to ensure positioning did not cause additional spinal cord compression. If significant signal changes are observed, the position of the cervical spine must be adjusted. Slight hypertension may also be used to improve perfusion of the spinal cord, and anesthetic agents should be checked. If none of these measures are able to restore MEPs or SSEPs to baseline, further repositioning should be done under fluoroscopic guidance to attempt to reduce the C1-2 subluxation as much as possible. Lateral fluoroscopy is used to confirm the positioning of the patient. Additionally, a metallic instrument can be placed along the side of the proposed C1-2 transarticular screw trajectory to ensure that the positioning does not obstruct the placement of the screw.