Answers to Questions about Chiropractic:
What Evidence Do You Have that
Neck Manipulation Can Cause a Stroke?
Samuel Homola, D.C.
As a longtime practicing chiropractor who specializes in upper cervical chiropractic adjustments, I have never seen a case of stroke caused by manipulating the neck. What makes you think that such treatment can cause a stroke?
Many case reports and the records of hospitals and insurance companies clearly suggest an association of stroke with upper neck manipulation. A simple review of the anatomy of the atlantoaxial joints in the upper cervical spine offers a plausible explanation of how inappropriate manipulation of the upper neck might cause stroke by damaging vertebral and internal carotid arteries.
The atlantoaxial joints (connecting the 1st and 2nd cervical vertebrae—the atlas and the axis), where the greatest amount of rotation takes place. These joints form the articulation between the atlas and the skull. They are designed primarily for flexion-extension (nodding of the head) and fit together like cups sitting in saucers. They are most vulnerable to injury since there are no intervertebral disc fibers and no interlocking joints to limit rotation. Normally, during active cervical rotation, all of the neck vertebrae move together, a little movement in each joint, allowing about 80 degrees of rotation right and left. The atlantoaxial joint, capable of about 50 degrees of rotation right and left, along with a small degree of lateral flexion and extension, is the only joint in the cervical spine where movement can occur alone, allowing excessive rotation when the chiropractor applies force to the neck
The vertebral arteries in the upper cervical area thread through the transverse processes of the atlas and then make a sharp turn to travel behind the atlas and enter the skull through the foramen magnum (a large opening in the base of the skull). Too much rotation of the skull or the atlas may overstretch the vertebral artery and the vertebrobasilar arteries that supply the back of the brain with blood.
Forced rotation forced by manual manipulation should not exceed 45 or 50 degrees in order to avoid kinking vertebral arteries. A head contact should not be used to force rotation of the neck. Sudden stretching of an atherosclerotic or fragile vertebral artery during a rapid manual rotation of the head might cause vertebral artery damage by overcoming the artery's compromised elasticity, causing a tear and bleeding in the inner lining of the artery and releasing clots that may travel to the brain.
There is, of course, a vertebral artery on each side of the neck, threading up through the transverse processes of cervical vertebrae from C6 to C1. Extreme rotation of the atlantoaxial joint in either direction stretches both arteries to some degree, more on one side or the other, depending upon the direction of rotation. Stretching or compromise of a vertebral artery is usually greater on the side opposite to head rotation. There is also a carotid artery (on each side of the neck) that does not pass through vertebral structures. The internal portion of the carotid artery passes through a small opening (the carotid canal) in the base of the skull to supply the anterior portion of the brain. Injury to the internal carotid artery can occur during vigorous neck manipulation but is less common than traumatic injury to a vertebral artery which passes through vertebral structures.
Dr. Homola is a second-generation chiropractor who has dedicated himself to defining the proper limits on chiropractic and to educating consumers and professionals about the field. His 1963 book Bonesetting, Chiropractic, and Cultism supported the appropriate use of spinal manipulation but renounced chiropractic dogma. His 1999 book Inside Chiropractic: A Patient's Guide provides an incisive look at chiropractic's history, benefits, and shortcomings. Now retired after 43 years of practice, he lives in Panama City, Florida.
This article was posted on September 12, 2014.