Thomas LC, Rivett DA, Bateman G, Stanwell P, Levi CR. Effect of selected manual therapy interventions for mechanical neck pain on vertebral and internal carotid arterial blood flow and cerebral inflow [published online June 27, 2013]. Phys Ther.. doi:10.2522/ptj.20120477.  

Manipulation of the cervical spine is rarely associated with serious adverse events involving compromise of the vertebral or internal carotid arteries. A search of the scientific literature, however, yields case studies and case series about patients who had strokes allegedly after receiving cervical manipulation performed by a health care professional.^1,2 Although laboratory studies have used ultrasonography to show that certain neck positions can alter vertebral and basilar arterial blood flow velocities, the clinical correlations of these findings have not been proven.^3-6 Using magnetic resonance (MR) angiography, Australian researchers Thomas et al sought to examine the effects of selected manual therapy techniques used for mechanical neck pain on blood supply to the brain. 

Twenty healthy adult participants (10 men and 10 women; mean [SD] age, 33 [11.9] years [range, 18-65 years]) underwent 3-T MR angiography with their necks in the following positions: neutral, rotation, rotation/distraction, C1-C2 rotation, and distraction. No statistically significantly changes in blood flow to the brain were found for any position, and no individual differences were found in blood flow between participants. In addition, the researchers did not find statistically significant differences in blood flow in any of the 4 cervical arteries for any position from neutral in participants. Each participant had normal anatomic structures. Of note, because this study used only healthy asymptomatic participants and investigated only a short section of the arteries, the results may not be applicable to clinical practice (ie, because of poor external validity). 

To limit the risks to participants in the study, volunteers were excluded if they reported any of the following: diagnosed inflammatory joint disease, history of serious cervical spine trauma (eg, fracture), any congenital disorder associated with hypermobility or instability of the upper cervical spine, diagnosed vertebrobasilar artery insufficiency (VBI), claustrophobia or discomfort in confined spaces (a standard contraindication for MR imaging), or any contraindication identified by an MR imaging safety screening questionnaire. 

In accordance with Australian Physiotherapy Association guidelines, all participants were assessed for cervical range of motion and tested for VBI prior to MR imaging examination. Participants who exhibited potential symptoms of VBI were excluded from the study; because of the sustained neck positions required for the study, these patients would have been at risk for brain ischemia. 

Blood flow to the brain does not appear to be compromised by positions commonly used in manual therapy. The next phase of this study would be to use symptomatic patients and to perform the manual procedures indicated by the clinical findings. Additionally, high-velocity, low-amplitude or spinal manipulative therapy should be employed to determine if these more forceful procedures cause any blood flow differences.