C1 and C2 screws

C1 screws

C1 from the side looks like a pan with a handle, the pan is the lateral mass and the handle is the ring.

Dissect down til you find the ring of  C1, then drop down along the ring deep to the lateral mass. The C2 nerve root is encased in a bunch of fascial tissue and surrounded by a venous plexus that bleeds a lot, very quickly. You can lose hundreds of CCs of blood before you know it. This is not the vert, its venous bleeding -- the vert is typically going to be lateral to you at this point - although always look at CT/MR beforehand and make sure no anomalous vert paths. 

The vert runs lateral to the lateral mass, then goes around and up along the superior aspect of the ring of C1. People say that as long as you are at the midpoint of C1 or more inferior, that you are safe- this is usually true but not always. People say you are safe as long as you are within 1cm of midline. this is usually true but not always. Always look at imaging ahead of time and measure and figure out where the vert is. 

Retract the C2 nerve root down. Your entry hole should be midpoint (in medial-lateral direction) along the lateral mass, and as superior as you can get (in superior-inferior direction) - see the red dot in CT above. Aim approx 10 degrees medial. This is because you really don't want to go lateral, as you risk hitting vert. Use fluoro to localize your angle superior-inferior, aiming for the anterior ring of C1. The temptation is to go high, because the ring of C1 may overhang down and push your hand down. if you go too high you might end up putting the screw through the O-C1 joint. You may have to drill off the inferior part of the ring of C1 to get the optimal angle. 

C2 screw 

There are three kinds of screws you can do: pars, pedicle, and lamina. 

Pedicle screws are the strongest, but also the highest risk of causing injury to the vertebral artery. They do these a lot in Japan. Possessing balls of steel is a pre-requisite for doing these. Pars screws are very strong and very safe as long as you stay behind the PLL.  Laminar screws are very strong and low risk but a pain to connect to the rest of your lateral mass screws with rods because of the angle; some people do these primarily, but most do them as a bailout if your pars screws break out. 

see the first CT in this page, see where the vert is. As long as you are behind PLL, you are almost always safe. 

When placing C2 pars screws, dissect down to where you can see the medial border of the ring of C2.  your entry point should be 2mm lateral, you aim slightly medial to avoid vert and superior. If you put an instrument between the facet of 2 and 3, it will give you the exact angle you need to aim in superior-inferior direction. 

Helpful videos:

https://www.youtube.com/watch?v=bqu8okFUUcU

Sublaminar wires

The principle is you put some sort of bony graft (i.e. iliac) between C1-2 and use cables to hold C1-2 onto the graft until bony fusion is achieved. Depending on the technique used, the rate of psuedoarthrosis is high. Needless to say, only works in instances where both C1 and C2 are structurally intact, and where decompression/lami is not required. 

Sonntag technique - iliac crest jammed between spinous process of C2 and the interlaminar space of C1-2, wires go under C1 lamina, and loop under C2 spinous process.