Some people refuse to go to a chiropractor because they fear
suffering a stroke after neck manipulation. Recent media attention
has focused on the claim of a cause-effect relationship between
chiropractic and stroke, yet little evidence actually supports
the hypothesis that neck manipulations can cause a stroke.
A recent study in the Journal of Manipulative and Physiological
Therapeutics makes this relationship seem even more implausible.
determine the extent of strain on the vertebral artery of
the neck during spinal manipulative therapy, six vertebral
arteries were utilized from five cadaveric specimens, with
only the necessary arterial loops exposed. Strains on the
arteries were measured during range-of-motion tests, diagnostic
tests and a number of manipulation procedures. Next, each
artery was removed and strained until failure on a materials-testing
machine, with the level of mechanical failure recorded.
Spinal manipulative therapy on the cervical spine caused
an average strain of about 2-6% over resting artery length
to the arterial loops, similar to strains measured during
range-of-motion tests. The failure tests showed that the vertebral
arteries could be stretched to 39-62% over resting length
before causing mechanical failure, however. The strain required
to damage the vertebral arteries was approximately nine times
greater than strain actually produced by spinal manipulation.
The researchers who conducted this study concluded that in
normal circumstances, typical chiropractic manipulations to
the neck are highly unlikely to tear the vertebral artery,
and that the strains measured on the arteries in this study
were within the range of those generated during normal activities.
In fact, the estimated occurrence of stroke following cervical
manipulations is approximately one per 6 million manipulations;
even in these cases, the manipulations aren't necessarily
the cause of the strokes. By comparison, a person's odds of
getting struck by lightning in his or her lifetime are much
higher: about one in 3,000.
Symons BP, Leonard T, Herzog W. Internal forces sustained
by the vertebral artery during spinal manipulative therapy.
Journal of Manipulative and Physiological Therapeutics
2002:25(8), pp. 504-510.
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