This week, we discuss an update to ground breaking cadaveric research conducted nearly 20 years ago by Drs. Walter Herzog, Bruce Symons and colleagues investigating cervical artery strains and forces experienced during neck manipulation. This new research is being conducted by an emerging star in chiropractic research - Dr. Lindsay Gorrell (with Dr. Herzog and others!).

Neck pain affects 30% to 50% of the adult population globally, resulting in a large proportion of musculoskeletal dysfunction worldwide. Cervical spine manipulation (CSM) has been shown to be an effective treatment for neck pain and is recommended in several clinical treatment guidelines. Neck pain is the second most common reason patients seek chiropractic care and CSM is the treatment modality most used during a chiropractic visit for this condition.

CSM frequently involves extension and rotation of the patient’s head and neck which has led some to suggest that the vertebral artery (VA) becomes stretched during the procedure, resulting in potential tissue damage including dissection. However, this theory is mainly supported in the literature by case studies which point to a temporal link between CSM and serious adverse events, such as VA dissection and stroke. On the other hand, population-based studies advocate that any temporal link is not likely causal. Instead of a causal association, it is likely that this temporal association between CSM and VA dissection is due to patients with early symptoms of cervical arterial dissection (neck pain and headache) seeking care from a chiropractic or medical practitioner and the dissection progressing to neurological involvement whether CSM is provided or not.

Previous cadaveric studies have shown that any changes in VA length during CSM are relatively small, much smaller than what is required to cause failure of the VA. Based on these findings, Symons et al. reported that a typical manipulative thrust was unlikely to mechanically disrupt the VA. However, another study reported VA failure following lower percentage of length changes and suggested that the VA may be susceptible to tissue damage with longitudinal elongation like what occurs during CSM.

No studies have tried to reproduce the results of the previous studies which quantified failure length changes along the full length of VA. Therefore, the purpose of this study was to measure and compare VA lengths under four conditions:

1. in situ, with the head and neck in arbitrary resting positions;
2. at peak elongation (length change) during spinal manipulation applied bilaterally to all cervical vertebrae;
3. at the occurrence of first force with elongation (i.e. when slack was removed); and
4. at mechanical failure.

NEW RESEARCH REVIEW: “Tensile Force in the Vertebral Arteries During Cervical Spine Manipulation Applied to Human Cadavers”