Vertebral Artery Dissection

Clinicians using manipulative therapy will be well aware of the potential for vertebral artery dissection and the testing protocols to evaluate competency of the vertebral arteries.  This is considered mandatory as a prerequisite for cervical manipulation on the basis that it can screen out potentially vulnerable patients.

Much of the literature published in the last decade has used investigative methods such as ultrasound and Doppler blood flow scanning to evaluate the effect of cervical positioning on Vertebral artery, Carotid artery and  Basilar system blood flow, which is fed by the vertebral arteries.  The fundamental premise of the vertebral testing protocol is that the vertebral artery can be occluded as a consequence of extra vascular pathology in the foramen transversarium or other parts of the posterior elements of the cervical spine.  The hypothesised effect of this is to both narrow the lumen for transmission of the vertebral artery and to increase the chances of compression as a result of change in orientation of each vertebral segment as the neck rotates.  Thus the principle of the test could be defined as a mechanism to explore extra vascular pathology and its potential to produce external compression.

The attraction of using Doppler ultrasound is that precise haemodynamics can be measured accurately in each of the functional positions which replicate the vertebral artery test protocol.  However, results from ultrasound studies are somewhat inconclusive because of the dynamic inter-relationship between the Carotid and Vertebral artery and the effect of diminishing flow volume in one system producing a compensatory increase in the other.  The net result is that total blood flow to the brain can be maintained by collateral routes.

Also of interest is the pathophysiology which has been quantified as a result of vertebral artery trauma.  This is referred to as vertebral artery dissection and involves varying types of tearing of the internal blood vessel wall.

Remember that the blood vessel wall is composed of three layers:

Tunica intima internally

Tunica media

Tunica adventitia externally

Depending on the location of tearing it may be classified as a sub-intimal dissection, which tends to result in stenosis of the artery or a sub-adventitial dissection, which tends to result in aneurysm formation.  Further consequences associated with vertebral artery pathology are the production of emboli, which may travel to remote sites in either the spinal cord or brain or secondary ischaemia because of emboli or blood vessel spasm associated with trauma.

There have been many mechanisms postulated to trigger these scenario’s, the most notable are:

Star gazing

Neck hyperextension

Sustained rotation

Severe whiplash trauma

Hairdressing (neck hyperextended over edge of sink).

We can see from the reported incidents with activities of daily living that there are similar positions involved as cervical manipulation procedures.  The question is whether we can accurately rely on the results of these test measures to define “at risk” patients and what can we conclude from positive and negative results using the existing testing protocols.  These issues and many more are discussed in a Vertebral Artery Testing online course available here at this link.

Any clinician utilising cervical manipulation needs to be aware of the relevant  issues to make an informed decision about interpretation of findings, risk benefits /  ratios and alternative treatment strategies.

Enjoy the clinical challenge.

David