Adjusting cadavers in the name of science!

A patient receiving a neck treatment in a chiropractor's office

Have you ever adjusted a cadaver? These researchers have, all in the name of good science!

We are all aware of the possible relationship between cSMT and cervical artery strokes (including those affecting the internal carotid artery, but most often in relation to the vertebral artery). The best epidemiological research we have suggests that cSMT is not causatively related to cervical artery stroke. Rather, the evidence strongly suggests that patients who experience a stroke after cSMT were likely seeking care for headache and/or neck pain that represent symptoms of a stroke already in progress (which would explain why there a temporal relationship has been noted with cSMT). As you should also know, neck pain and headache are both common symptoms of cervical artery strokes.

From a mechanistic perspective, it has been argued that cSMT places undue strain (elongation) on the vertebral arteries, which could lead to damage and subsequent dissection. At the same time, it is well-accepted that cervical arteries must, and do, accommodate for a wide range of normal head and neck movements without sustaining injury. Since variety of head and neck movements (including cSMT) have been temporally related to vertebral artery strokes in the literature, it is worth studying the mechanical forces cSMT imparts on the vertebral arteries.

Previous studies by Drs. Bruce Symons, Walter Herzog and colleagues evaluated strains on cervical arteries (vertebral and internal carotid) during cSMT and range of motion (ROM) procedures in a cadaver model. The results of these studies suggest that cSMT results in strains that are an order of magnitude below failure strain for the vertebral artery, and that maximal strain on the internal carotid artery actually occurs during ROM testing! These original studies and have recently been replicated (again in a cadaver model), with Dr. Lindsay Gorrell and colleagues (including Walter Herzog) now suggesting that in resting head and neck positions, there is actually slack in the vertebral artery. They also discovered that cSMT results length changes that remain below the slack length, indicating that cSMT does not stretch the vertebral artery at all.

This study aimed to advance our knowledge by quantifying not only the total vertebral artery elongations during cSMT, but also the length change of the vertebral artery from the neutral anatomical reference position to the pre-manipulative position, and from the pre-manipulative position to the end of the manipulative thrust. A secondary purpose was to compare the vertebral artery elongations in the pre-manipulative phase, the thrust phase, and the total elongation (from reference position to the end of the thrust) to the vertebral artery strains observed during passive ROM testing.

RESEARCH REVIEW: Vertebral Artery Strain During Passive Neck Movements and Cervical Manipulation in Cadavers

This paper was published in the Journal of Bodywork & Movement Therapies (2024)

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