By Marcello Cherchi, MD PhD
For patients
Some practitioners, particularly physical therapists, maintain that turning the head (while keeping the trunk still) and monitoring for whether this provokes any symptoms, is a way of “testing” the vertebral artery — one of the arteries that supplies blood to the brain. Researchers disagree about whether this test is useful.
For clinicians
Practical summary
“Vertebral artery testing” (VAT) refers to the practice (mostly by physical therapists) of rotating the patient’s head around the vertical axis (while keeping the trunk stationary) and monitoring for symptoms, in the belief that this can assess the patient’s risk of vascular compromise from further neck manipulations. Rotation of the head with respect to the shoulders exerts compressive and torquing forces on the vertebral arteries as they pass through the cervical vertebral foramina, particularly between C1 and C2. One risk of extrinsic compression of the vertebral artery is transient occlusion of flow, sometimes manifesting as bow hunter syndrome. A risk of extrinsic compression and torquing is vertebral artery dissection. Despite study of animal models, human cadaveric material, and in-vivo imaging studies, there is disagreement in the literature about how significant these risks are, though most such literature recommends caution in patients with known vascular risk factors. Thus the clinical value of “vertebral artery testing” (VAT) in assessing such risks is unclear; most of the literature, and meta-analyses of that literature, conclude that VAT is not useful.
Discussion
After the vertebral arteries branch off the subclavian arteries they ascend through cervical vertebral foramina at each level before joining to form the basilar artery.
This is shown in the Figure below, from Shafafy and colleagues (Shafafy et al. 2017).
Head movement in yaw (rotation of the head around the vertical axis with respect to the shoulders) exerts torque and stretch forces on the vertebral arteries as they pass through the arterial foramina in the cervical vertebrae, particularly in the segment between the C1 and C2 foramina.
This is shown in the Figure below from Choi and colleagues (Choi et al. 2013).
The effects of these forces on the vertebral arteries raises two main concerns. The first is transient occlusion of the lumen due to extrinsic compression; this is sometimes referred to as bow hunter syndrome of which there are case reports and small series (Go et al. 2013; Hong et al. 2022; Kamouchi et al. 2003; Li et al. 2019; Lu et al. 2010; Sakaguchi et al. 2003; Sarkar et al. 2014; Sorensen 1978; Takafumi et al. 2024; Weintraub and Khoury 2004; Xue et al. 2023; Zaidi et al. 2014), and broader reviews (Cornelius et al. 2012; Duan et al. 2016). The second is injury to the vascular wall resulting in vertebral artery dissection (Albuquerque et al. 2011; Chen et al. 2006; Haldeman et al. 2001; Vibert et al. 1993), which can result in stroke (Charles et al. 1992; Chen et al. 2006; Choi et al. 2006; Eliezer et al. 2019).
Despite analyses of possible risk factors (Thomas et al. 2011), it is difficult to predict which individuals are vulnerable to these effects. This may be due in part to the considerable variability in the normal anatomy of vertebral arteries (Tudose et al. 2023).
Canine (Kawchuk et al. 2004) and porcine (Licht et al. 1999) animal models have been proposed for studying vertebral arterial mechanics, and while interesting, they comprise an approximation of the situation in humans.
Human cadaveric studies of vertebral arterial mechanics generally conclude that, “The engineering strains during cervical spinal manipulations… impart stretches on the VA [vertebral artery] that are well within the normal physiologic range of neck motion” (Wuest et al. 2010), and that “SMT [spinal manipulative therapy] resulted in strains to the VA that were almost an order of magnitude lower than the strains required to mechanically disrupt it” (Symons et al. 2002). Not all cadaveric studies reach such conclusions (Li et al. 1999).
Doppler ultrasonography is a commonly used approach for studying in vivo vertebral artery flow during cervical manipulations (Haynes 2000; Haynes et al. 2000; Shum et al. 2017), though other modalities include MR angiography (Haynes et al. 2002). The majority of vascular imaging studies observe no significant changes in various head-on-neck positions (Erhardt et al. 2015; Haynes et al. 2002; Leenaerts et al. 2020; Mitchell 2007; Moll et al. 2023; Thiel et al. 1994; Yelverton et al. 2020; Zaina et al. 2003); a minority of studies express a dissenting opinion (Arnold et al. 2004; Mitchell et al. 2004; Mitchell 2003; Thomas et al. 2015).
An extensive systematic review conducted by academic physical therapists (Richter and Reinking 2005) concluded that:
“The VA [vertebral artery] test has been called a clearing test, implying that a negative test ‘clears’ the patient of VBI [vertebrobasilar insufficiency] and allows cervical mobilization or manipulation if indicated. The diagnostic accuracy data we found do not support this interpretation… We believe the strength of the evidence for VA testing is weak” (Richter and Reinking 2005).
Several studies conclude that overall the evidence in support of vertebral artery testing is weak (Mitchell 2008; Richter and Reinking 2005) and that more studies are needed before any firm conclusions can be drawn (Rivett et al. 1999). Some authors take the more extreme position that vertebral artery testing should be abandoned altogether (Hutting et al. 2020), while others conclude that it would be premature to do so (Thomas and Treleaven 2020).
Most studies expressing caution take the position that cervical spine manipulations should be avoided in patients with a history suggestive of vertebral artery dissection (injury, neck pain) or known vascular risk factors (Thiel and Rix 2005), whereas in individuals without such risk factors (Yelverton et al. 2020), cervical spine manipulations are safe.
Our reading of this literature is that:
- The overall risk from the more rapid and larger-amplitude head-on-neck movements involved in chiropractic manipulation logically produces more robust forces, from which the risk of sequelae (such as vertebral arterial dissection) appears to be higher.
- In contrast, the slower and smaller head-on-neck movements entailed by, for example, vestibular rehabilitation therapy management of benign paroxysmal positional vertigo (BPPV), exert more modest forces, with commensurately lower risk. The risk can be further reduced through modification of standard maneuvers; for example, when treating lateral canal BPPV, rather than rotating the head 90 degrees to either side (with respect to the trunk) during the supine roll test, the treating clinician can rotate the entire body, thereby keeping the head-on-neck position stable (with no relative rotation), while still achieving the head positioned with respect to gravity such that canaliths can be repositioned.
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