Trans articular screw insertion

The entry point of the screw is 3-4mm cranial to the C2-C3 facet joint and in the midpoint of the pars mediolaterally.

The endpoint of the screw is such that it just perforates the anterior arch of C1 and has adequate purchase in the lateral mass of C1.

Under lateral fluoroscopy, the landmark for this in the anterior posterior plane is the posterior cortex of the C1 tubercle.

To determine where to insert the guidewire through the skin, hold a guidewire outside the patient under fluoroscopy.

The guidewire trajectory should be aimed such that the tip ends up somewhere between the bottom 25-50% of the anterior tubercle of C1 (see illustration).

A straight guide wire going from the endpoint of to the starting hole will determine where the skin incision needs to be made.

Make a 10 mm skin incision at the K-wire entry point.

Place a small burr hole as the starting point for the guide wire.

Insert and advance the guide wire under fluoroscopic guidance until the tip is docked at the prepared starting point.

Using a wire driver, advance the guide wire until it reaches the end point.

In the lateral fluoroscopic view, the tip of the drill should not advance further than the posterior cortex of the C1 tubercle.

Take care to prevent penetration of the anterior cortex.

Under fluoroscopic guidance, drill, tap, and insert the screw.

During the drilling and tapping, check fluoroscopy to make sure that the guidewire is not being advanced. Failure to do so can result in the guidewire injuring structures in the retropharyngeal region.