Spinal manipulations do not overstrain internal carotid artery

By Lucy Piper, Senior medwireNews Reporter

Chiropractic cervical spinal manipulations do not pose undue stress and strain on the internal carotid artery (ICA), researchers affirm.

They found that elongations of the ICA and associated strains are much smaller during high-speed, low-amplitude cervical spinal manipulations than they are during range of motion (ROM) testing.

"We conclude from this result that SMTs [spinal manipulation therapies] are less likely to produce stretch-induced damage to the ICA than normal, everyday head and neck movements involving the full possible ROM," say Walter Herzog (University of Calgary, Alberta, Canada) and colleagues.

Using six cadavers, the team compared the peak and average strains of the ICA during cervical spinal manipulations, given by experienced chiropractors, with the corresponding strains obtained during ROM diagnostic testing of the head and neck.

The results, published in the Journal of Manipulative and Physiological Therapeutics, show that the mean and maximal ICA strains for the ROM testing were significantly greater than those for the spinal manipulation therapy.

"Not only was this result statistically significant, but also it was observed individually for each clinician and each ICA, that is, in 36 different clinician/ICA combinations," the researchers note.

The mean of all maximal ICA strains obtained during spinal manipulation was 28% of that obtained for the ROM testing, and was 10% of the ultimate failure strain of the ICA.

Herzog et al note that they were very careful to make sure that passive ROM was similar to active ROM, by stopping as soon as the first tangible force was detected.

They recognize the limitations of using cadaveric specimens for their trial, including the need to artificially inflate arteries, but say that "there is no reason to believe that the strains measured here would be any different than the strains for the same head and neck movements in live patients."

The researchers therefore conclude that "cervical SMT, as performed by the trained doctors of chiropractic in this study, did not appear to place undue strain on the ICA and thus does not seem to be a factor in ICA injuries."

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