I’ve just been on a course that challenged my thinking about how joints move. We were asked to think about how many ways a spinal joint can move.
Classic thinking is that it can flex (bend forward), extend (bend backwards) side bend left, and right and rotate left, and right. Thinking a little harder and the joint can also translate, that is traction or compression can be applied and obviously it can have varying combinations of the above.
But, in order to achieve left rotation at the C3-4 joint, that is C3 vertebra rotating left relative to C4 vertebra there are 5 different things that could be happening
C3 could be rotating left on a fixed C4
C4 could be rotating right under a fixed C3
C3 could be rotating left and C4 could be rotating right
C3 and C4 could both be rotating left but C3 is moving faster, and
C3 and C4 could both be rotating right but C3 is moving more slowly
That works for all of the directions of motion.
Why is that important, beyond an interesting brain teaser?
Firstly it can give us more information. If C3 won’t easily rotate left on C4 but C4 will rotate right on C3, perhaps the problem isn’t with C3-4 but instead C3 cannot rotate right under C2
Secondly, it gives more treatment options. If you can’t turn your head to the left without pain, perhaps, instead you can fix your stare on a point and reach forward with your left arm, rotating your shoulder girdle to the right. That is still rotating the top part of your neck to the left relative to the bottom part but is coming at it bottom up, rather than top down. This can be incredibly powerful and can be applied in all ranges of motion throughout the spine