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Research Review By Dr. Demetry Assimakopoulos©


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Date Posted:

January 2020

Study Title:

Effect of cervical manipulation on vertebral artery and cerebral hemodynamics in patients with chronic neck pain: a crossover randomised controlled trial


Moser N, Mior S, Noseworthy M, Côté P, Wells G, Behr M & Triano J

Author's Affiliations:

Department of Graduate Studies, Canadian Memorial Chiropractic College, Toronto, Ontario, Canada; Faculty of Health Sciences, University of Ontario Institute of Technology, Oshawa, Ontario, Canada; Radiology, McMaster University Faculty of Engineering, Hamilton, Ontario, Canada; Faculty of Kinesiology and Physical Education, University of Toronto, Ontario, Canada; Department of Medicine, Division of Physical Medicine and Rehabilitation, University of Toronto, Ontario, Canada.

Publication Information:

BMJ Open 2019; 9: e025219.

Background Information:

In spite of a wealth of epidemiological evidence to the contrary (1, 2), many clinicians and members of the general public still believe that neck manipulation increases the risk of vertebrobasilar artery (VBA) stroke (3-5). Prior hemodynamic studies have failed to demonstrate any changes in vertebral blood flow or velocity following cervical manipulation in healthy populations (6, 7). However, the impact of cervical spinal manipulation on vertebral artery hemodynamics has not been assessed in patients with neck pain. As such, the authors endeavored to determine whether cervical spinal manipulation leads to meaningful changes in vertebral and cerebral hemodynamics, compared to neutral or end-range neck rotation postures in adults with chronic neck pain. They secondarily attempted to compare the functional connectivity of the default mode network (DMN) in different neck positions.

Pertinent Results:

A total of 20 patients (14 female and 6 male) aged 23-66 years were enrolled. The average NDI score was 13/50 (standard deviation [SD] +/- 6.4) with an average neck pain intensity of 5/10 (SD +/- 2.1) and an average neck pain duration of 5.3 years (SD +/- 5.7).

Evaluation of Hemodynamics During ROM & SMT:
  • When compared with the neutral neck position, maximal neck rotation and cervical manipulation (SMT) did not significantly alter posterior cerebral or cerebellar perfusion.
  • The authors identified a significant difference in contralateral vertebral artery blood flow between neutral and maximal neck rotation, as well as between cervical manipulation and maximal neck rotation.
  • The authors also identified a significant difference in contralateral vertebral artery blood velocity between neutral and cervical manipulation, and between neutral and maximal neck rotation.
  • They did not identify any significant differences between the cervical manipulation and maximal neck rotation positions.
Default Mode Network (DMN):

The researchers identified a significantly increased DMN functional connectivity post-manipulation (p < 0.05). Specifically, when compared to the resting position, the following areas significantly increased functional connectivity: uvula, cerebellar tonsils, left fusiform gyrus and left middle temporal gyrus, right middle temporal gyrus, right middle occipital gyrus, bilateral cuneus, left precuneus and left middle occipital gyrus.

The authors demonstrated a significant order effect for contralateral vertebral artery blood velocity (p = 0.02). Specifically, the contralateral vertebral artery velocity was higher for which ever condition was performed first. (Writer’s comment: This means that if cervical manipulation occurred first, contralateral VA velocity was greater after performing the manipulation, compared to maximal cervical rotation. Conversely, if end-range cervical rotation was performed first, it demonstrated greater contralateral VA velocity compared to cervical SMT).

Adverse Events:

No major adverse effects were reported. One minor adverse event of post-analysis neck soreness was reported. However, the neck soreness was attributed to having to lay motionless on the hard scanner bed by the patient.

Clinical Application & Conclusions:

The authors used an MRI scanner to measure the effect of various head positions on cerebrovascular and vertebral artery blood flow/velocity to the posterior cerebrum and cerebellum. They demonstrated that significant perfusion changes occurred within these brain regions. Specifically, they observed similar changes in contralateral vertebral artery blood velocity following both cervical manipulation and maximal neck rotation. Given that changes in contralateral vertebral artery blood velocity were similar between conditions, the researchers attributed the above-mentioned changes in blood velocity to head turning, as opposed to cervical manipulation thrust. These results support the notion that the association between cervical manipulation and stroke is due to protopathic bias (1). NOTE: protopathic bias occurs when a therapeutic agent (SMT) is applied for the early symptoms (ex. neck pain or headache) of an occult disease (vertebrobasilar artery stroke) and, when the patient later develops the full manifestation of the disease (stroke), the therapeutic agent (SMT) is mistakenly assumed to have been its “cause”.

In comparison to a neutral neck position, both maximum voluntary neck rotation and cervical manipulation resulted in significantly increased functional connectivity throughout the DMN. These changes in blood volume or metabolic activity within the DMN may be a consequence of sensory stimulation and patient self-awareness from handling a body region such as the neck. This area requires more research.

Study Methods:

The authors conducted a crossover RCT to assess positional effects on cerebrovascular hemodynamics. Patients were recruited from the Canadian Memorial Chiropractic College teaching clinics between September 2016 and April 2017, based on the following inclusion criteria:
  • ≥ 18 years of age
  • Chronic neck pain ≥ 3 months
  • Grade I-II neck pain
  • Were prescribed cervical SMT
  • Provided written informed consent
The exclusion criteria were the following:
  • History of neck-related arm pain within the last 6 months
  • Any current or previous history of neurological symptoms such as facial or extremity weakness, abnormal sensation in the face, body or extremities, uncontrolled movements, abnormal gait, dizziness, unexplained nausea/vomiting, difficulty with speaking or swallowing
  • Past or present headaches rated ≥ 6/10 in the last 3 months
  • Any contraindication to MRI
  • History of using drugs that affect blood flow
Patients were additionally asked to refrain from engaging in vigorous physical activity, or consuming alcohol or caffeine 1-day before their scheduled participation.

Each participant filled in standard demographic and Neck Disability Index (NDI) forms. Patients also reported their height, weight, neck/headache pain intensity and neck pain duration. Participants then underwent a physical assessment, and MRIs of the upper cervical spine and brain in the neutral position.

Participants were then randomized to one of two interventional sequences: 1) maximal neck rotation followed by upper cervical manipulation; or 2) upper cervical (C1-2) manipulation followed by maximal neck rotation. There was no washout period between interventions. Maximal neck rotation was achieved by instructing participants to rotate their head as far as comfortably possible in the direction opposite to the side of the clinical symptoms. The degree of maximal neck rotation was measured by an inclinometer and the position was held for 1-minute before returning to neutral neck position for MRI sequencing. The cervical manipulation procedure was a high-velocity, low-amplitude impulse with a targeted contact at the C1-C2 articulation on the side of discomfort. The manipulation was performed with the head in combined axial rotation, flexion and lateral flexion postures, with the patient laying on the scanner bed in the MRI room.

The primary outcome measure was cerebrovascular hemodynamics within the vertebral arteries and posterior cerebrum measured by MRI. The secondary outcome measure was functional connectivity within the default mode network (DMN). Participants were scanned 3-times per session: baseline, and in the two above-mentioned procedures. Each participant was observed for 1-hour after testing. Reported adverse events included local soreness and pain in the area of applied test manoeuvres (minor adverse events). There were no major reported side-effects.

Study Strengths / Weaknesses:

  • The design ensured control of cofounders and provided statistical efficiency.
  • The authors used phase-contrast MRI blood flow measurements because of its greater sensitivity compared with ultrasonography and because it is the criterion standard for the diagnosis of vertebrobasilar stroke and for quantifying blood flow.
  • The analysis was restricted to a very short duration (avg. 115 sec.) following the testing manoeuvres. Real-time measures are not currently technically feasible, and transient effects of various neck positions on vertebral artery and cerebrovascular hemodynamics may have been missed. As such, the results only describe post-procedural effects and cannot be generalized to the possible effects occurring during the test manoeuvres.
  • The possibility that neck pain participants exist who exhibit idiosyncratic responses cannot be excluded.

Additional References:

  1. Cassidy JD, Boyle E, Cote P, et al. Risk of vertebrobasilar stroke and chiropractic care: results of a population-based case-control and case crossover study. Spine 2008; 33(4 Suppl): S176–83.
  2. Boyle E, Cote P, Grier AR, et al. Examining vertebrobasilar artery stroke in two Canadian provinces. Spine 2008; 33(4 Suppl): S170–5.
  3. Albuquerque FC, Hu YC, Dashti SR, et al. Craniocervical arterial dissections as sequelae of chiropractic manipulation: patterns of injury and management. J Neurosurg 2011; 115: 1197–205.
  4. Ernst E. Manipulation of the cervical spine: a systematic review of case reports of serious adverse events, 1995-2001. Med J Aust 2002; 176: 376–80.
  5. Norris JW, Beletsky V, Nadareishvili ZG. Sudden neck movement and cervical artery dissection. The Canadian Stroke Consortium. CMAJ 2000; 163: 38–40.
  6. Quesnele JJ, Triano JJ, Noseworthy MD, et al. Changes in vertebral artery blood flow following various head positions and cervical spine manipulation. J Manipulative Physiol Ther 2014; 37: 22–31.
  7. Erhardt JW, Windsor BA, Kerry R, et al. The immediate effect of atlanto axial high velocity thrust techniques on blood flow in the vertebral artery: A randomized controlled trial. Man Ther 2015; 20: 614–22.

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