At the completion of this chapter, the reader will be able to:
Describe the anatomy and distribution of the vertebral artery.
Describe the four commonly recognized portions of the vertebral artery.
Outline the causes of vertebral artery occlusion or compromise.
Recognize the characteristics of vertebral artery occlusion or insufficiency.
Describe various special tests used to assess the patency of the vertebrobasilar system and their diagnostic value.
The vertebral artery (VA), a component of the vertebrobasilar artery (VBA) system, supplies 20% of the blood to the brain (primarily the posterior cranial fossa), with the remaining 80% being supplied by the carotid system.1 The first studies of the VA were recorded as far back as 1844.2 Since that time, recognition of the importance of the VA has continued to grow, and it is now discussed in more detail than any other artery by physical therapists. For this reason, the VA is afforded its own chapter. To fully comprehend its significance, a review of its anatomy and function is in order.
The VBA system consists of three key vessels: two VAs and one basilar artery. The basilar artery is formed by the two VAs joining each other at the midline (Fig. 24-1).
The vertebral artery and its relationship to the cranial arteries. (Reproduced with permission from Morton DA, Foreman KB, Albertine KH: The Big Picture: Gross Anatomy. New York: McGraw-Hill, 2011.)
Along its course, the artery can be viewed as having four portions: proximal, transverse, suboccipital, and intracranial.3,4
This portion runs from the origin of the artery to its point of entry to the cervical spine. The VA usually originates from the posterior surface of the subclavian artery, but it can also originate from the aortic arch and common carotid artery.5
The VA runs vertically, slightly medial, and posteriorly lateral to the longus colli and medial to the anterior scalene muscles to reach the transverse foramen of the lower cervical spine, although its exact direction is dependent on its exact point of origin. Its anomalous origin in this region has been suggested as a potential factor increasing the chance of blood flow compromise due to compression by the longus colli or scalene muscles.
In approximately 88% of individuals, the artery enters the transverse foramen of C6, but it has been shown to enter as far superior as the transverse foramen of C4.6
Tortuosity and compression of this portion of the artery are common. The reasons for this can be congenital or muscular (resulting from compression by the longus colli and medial aspect of the anterior scalene), or a consequence of advancing years.