Research Review By Dr. Michael Haneline©


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Date Posted:

September 2022

Study Title:

Kinematics of the head and associated vertebral artery length changes during high‑velocity, low‑amplitude cervical spine manipulation


Gorrell L, Kuntze G, Ronsky J et al.

Author's Affiliations:

Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Alberta, Canada; Department of Chiropractic Medicine, University Hospital Balgrist and University of Zurich, Switzerland; Schulich School of Engineering, University of Calgary; Canadian Memorial Chiropractic College, Toronto, Canada

Publication Information:

Chiropractic & Manual Therapies 2022; 30: 28.

Background Information:

High-velocity, low amplitude cervical spine manipulation (CSM) is an effective treatment for neck pain that is commonly sought by patients and is recommended in numerous clinical practice guidelines (1). Nonetheless, some are concerned about the safety of CSM (2), especially about CSM that involves head and neck extension/rotation and possible stretch and damage to the inner lining of the vertebral artery (VA) resulting in arterial dissection and subsequent stroke (3).

Prior studies have shown that head angular displacements during CSM are small and do not exceed the normal physiological range of motion (4). However, one study reported that angular head displacements at the pre-manipulative position approached the extent of upper cervical active range of motion.

The elongation response of the VA to CSM and passive ranges of motion has been investigated in several studies, with reports of arterial length changes for specific regions or along the full length of the artery. Head and neck rotation contralateral to the side of VA instrumentation resulted in the greatest changes in VA length at the V3 segment (C1/C2 level) during both CSM and passive ranges of motion. These changes in VA length during CSM were typically lower than changes measured during passive range of motion testing, and they did not approach published length changes that result in failure (which is about 12% elongation on average).

However, the kinematics of the head relative to the sternum along with associated VA length changes during the thrust phase of CSM delivered at each level of the cervical spine have not been investigated. Therefore, it is not known whether VA length changes vary when CSM thrusts are applied to different levels of the cervical spine.

Because of gaps identified in previous research, the purpose of this cadaveric study was to systematically quantify the angular displacements of the head relative to the sternum and the associated VA length changes during the thrust phase of two types of CSM (rotation and lateral flexion), applied bilaterally, to each level of the cervical spine (C1–C7). The authors hypothesized that there would be no differences in VA length changes during CSM applied to the different vertebral levels.

Pertinent Results:

168 thrust cervical manipulations (CSMs) were delivered to the cadaveric donors, with 165 of them being used in the analysis.

No significant differences in VA length changes during CSM applied to any of the different vertebral levels were detected. VA length changes during the thrust phase of CSM were small regardless of the type of CSM that was used or the side or level it was applied. VA length changes were greatest when CSM was applied during ipsilateral rotation.

There was considerable variability in VA length changes measured in the whole artery and V3 segment across different donors and clinicians.

Clinical Application & Conclusions:

The main conclusion of this study is that CSM thrusts created small head angular displacements and VA length changes. Though still considered small, average VA length changes were largest during rotational procedures.

Given that CSM thrusts were shown to produce small head angular displacements and VA length changes in this study, clinicians who utilize CSM should be aware that subsequent VA injury is less likely than what some authors have suggested (5).

Nonetheless, some clinicians may wish to limit even small VA length changes during CSM by modifying the types of CSM they use (based on these study results, this could be best accomplished by limiting rotation).

Finally, articles like this may also be useful in defending legal liability claims that arise from VA dissection or damage in temporal relationship to CSM.

Study Methods:

This study involved 3 male cadavers (88 ± 6 years old) which were visually inspected and found to be free of substantial anatomic variations in the origin, course, or appearance of the vertebral arteries. There were, however, some minor cervical spine osteophytes present in all donors which did not affect their passive ranges of neck motion assessed prior to (anatomical) dissection.

An anatomist with 10 years of experience performed blunt dissections of the anterior cervical region to expose the VAs. Each VA was individually instrumented with 2 mm piezoelectric ultrasound crystals, with 8 crystals inserted along each artery’s entire length. Next, 3 mm stainless steel bone pins were inserted into the skull and sternum and marker spheres were affixed to each bone pin.

CSM was performed by 3 experienced clinicians, with data being collected from 2 clinicians for each donor. The order of CSM delivery was randomized to prevent order effects. Manual, high-velocity low-amplitude CSM thrusts (rotation and lateral flexion) were applied bilaterally to each cervical vertebra with the cadavers supine.

VA length changes were acquired using a SonoSoft system, which captured signals from the ultrasound crystals. The force–time profiles for each CSM were recorded using a thin, flexible pressure pad placed securely between the clinician’s contact and the donor’s neck which enabled identification of the time of the thrust onset and the peak force (end of the thrust phase). Three-dimensional (3D) angular displacements of the head relative to the sternum were recorded using an eight-camera optical motion capture system.

Study Strengths / Weaknesses

This was a well-done study on the effects of CSM on head angular displacements and length changes of the VA. Great care was employed to ensure accuracy of the measurements that were taken and that extraneous factors were limited. However, the study did not involve living subjects, rather, cadavers of elderly subjects were used, which are not directly generalizable to the clinical setting (especially to the age range of patients that may experience a VA issue in relation to CSM, which is typically younger patients between 20-50 approximately).

The authors appropriately mentioned the following study limitations:
  • Soft tissues were dissected away from the cadavers which could have increased the extent of head displacements during CSM as compared to living subjects. Thus, the (already small) VA length changes may have actually been overestimated here as compared to what would occur in a clinical situation in a live person.
  • The temperature of the cadavers was lower than that of living subjects which could have affected biomechanical responses of the soft tissues, such as limited flexibility and increased stiffness.
  • In living patients, the VA changes are not only longitudinal, as measured in this study, but also circumferential and radial due to pulsatile blood pressure causing strains in all directions.
  • The VA is comprised of three separate layers which may react differently to CSM in comparison to the entire VA; however, no attempt was made to measure these possible differences.
  • Piezoelectric crystals can only measure in a straight line between each crystal; however, the VA is not straight and is relatively loose.
  • VA length changes were measured only for the thrust phase of CSM and no standardized reference comparisons are available. This limits the ability to make statements about potential damage of the VA due to over-stretching.

Additional References:

  1. Whalen W, Farabaugh R, Hawk C, et al. Best-practice recommendations for chiropractic management of patients with neck pain. J Manip Physiol Ther 2019; 42(9): 635–50.
  2. Biller J, Sacco RL, Albuquerque F, et al. Cervical arterial dissections and association with cervical manipulative therapy: a statement for healthcare professionals from the American heart association/American stroke association. Stroke J Cereb Circ 2014; 45(10): 3155–74.
  3. Assendelft W, Bouter L, Knipschild P. Complications of spinal manipulation: a comprehensive review of the literature. J Fam Pract 1996; 42(5): 475–80.
  4. Klein P, Broers C, Feipel V, et al. Global 3D head-trunk kinematics during cervical spine manipulation at different levels. Clin Biomech 2003; 18(9): 827–31.
  5. Ernst E. Adverse effects of spinal manipulation: a systematic review. J R Soc Med 2007; 100(7): 330–8.

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