One thing I came to believe is that jugular compression between the C1 lateral mass and the styloid process is actually very both complex and complicated phenomena.
The skull base is supposed to be able to flex forward and backwards on top of the C1, about 30 degrees. Not slide or glide with the point between C1 lat.mass and the SP remaining in stationary, but rotate like on a horizontal hinge.
According to some sources the C0/C1 joint is responsible for as much as 20-50% of the whole neck flexion/extension ROM.
Which means, the distance between the SP which is attached to the skull and C1 lat mass is supposed to vary, leading to dynamic, changing compression levels on the structures in-between, therefore the IJV too.
So, it seems some of the roads lead to impacted biomechanics possibly caused by muscular spasms.
Now whether it’s a self-reinforcing mechanism (impacted SP/SH cause muscle spasms, causing further immobility) is up to debate, at least in my case it was obvious that long SPs/ossified ligaments were causing a lot of resistance (and pain) whenever I moved them outside of their “settled/preferred” position, leading to malignant movement patterns. Removing the styloids helped to break this cycle.
For further information, check this one:
So my conclusion is, the whole concept of the IJV compression between the C1 and SP as a static constant thing might be:
a) accurate in case there is a pathology causing C0/C1 immobility (congenital fusion, arcuate foramen etc), or the angle of SP at “normal” or even “extended” position is so bad that it causes the IJV compression
b) accurate in case it may be caused by stiff and shortened deep neck flexors and overstretched/weak neck extensors, or any other combination of agonist and antagonist muscle imbalance causing improper neck movement
c) inaccurate in cases the muscle spasm is due to the postural or other reasons, and surgical resection doesn’t guarantee any results unless the postural and muscular issues are addressed either before or after the surgery.
Upd:
This one shows how much (approximately) the SP is supposed to move away from the C1 during extension.
And this is the whole cervical spine in action during flexion/extension
