The Upper Cervical Spine

Basic Anatomy

The cervical spine has to strike a balance between mobility (to allow for freedom of the teleceptors) and stability (to protect the spinal cord), all while providing the skeletal support necessary to allow us to carry our heads around all day without becoming exhausted. 

It is composed of 7 vertebrae. While the bottom 5 are largely alike, the top two--the atlas and the axis--are unique. This post will focus on the interfaces between the upper two vertebrae and the skull.

  1. C0-C1: The Occipito-Atlanto (OA) Joint
  2. C1-C2: The Atlanto-Axial (AA) Joint

Adapting the Skeleton

While this part of the project is going to be slightly more involved than the jaw, it will only require 4 drill holes. So take heart, you'll be done soon!

 


1. Prep the skull

The first step is to drill two holes through the middle of the occiptal condyles using a 3/16 bit. These need to be large enough to accommodate a 1/8'' bungee cord.

Top view of occipital condyle drill path

Bottom view of condyle drill path


Holes drilled through the Atlas and axis where they will be in contact with each other

Holes drilled through the Atlas and axis where they will be in contact with each other

2. Join the axis and atlas

Next up is to drill holes through the atlas and axis as show at right. It helps to position the atlas beneath the skull and mark where the holes from step 1 meet up with the surface of the atlas. Repeat for drilling into the axis in the same way to ensure your pieces will fit together well.

You will be left with two corridors running through the occipital condyles, atlas and axis. 


With the tunnels for the cords in place, cut two 8'' sections of 1/8'' cord. Tie a knot at the end of each and thread them through these tunnels, beginning at the axis and working your way up. Within the skull, tie the cords together and assess the mobility at each of the segments. Play with the tension until you're happy with the balance between mobility/stability.

knots holding the cord in place. note the how the ends are singed to prevent fraying

Thread through C1 above

Tie the two pieces together

Upper Cervical Spine Done!


How does this stack up to the real thing?

There are a few basic movements worth paying attention to here: flexion/extension and lateral flexion at the OA joint, and rotation at the AA joint. Check out the video below and I hope you'll agree that this is a substantial improvement over most of the anatomical models that you'll find out there.