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Glendale, CA 91206
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Big Neck Bones, Small Spinal Canals: Japanese Men Have It Bad

Posted on: 03/13/2002
As a group, it seems that Japanese people have an unusual amount of myelopathy. Myelopathy is the medical term for pressure against the spinal cord. When this occurs in the neck, it is called "cervical myelopathy." Anything that causes the spinal canal to narrow in size can cause this problem. Examples include arthritic changes, inflammation, trauma, or problems in the bone structure at birth.

Every bone in the spine has an opening for the spinal cord to pass through. This is called the spinal canal. Having a narrow spinal canal is the main reason people end up with cervical myelopathy.

Gender is also an important factor in cervical myelopathy. According to researchers, Japanese men have this problem more often than Japanese women. A third risk factor is large spine bones. Is there a relationship between these three risk factors?

To answer this question, researchers looked at X-rays of people newly hired by a large company in 1975. This company required a physical exam and spine X-ray of all its new employees. There were 107 men and 116 women in all.

Three measurements were taken from each X-ray: (1) the height of the individual neck bone, (2) the size of the neck bone from front to back (diameter), and (3) the size of the spinal canal opening.

The researchers found that the height of the neck bone had no connection to the size of the spinal canal. This was true for both men and women. However, in men only, the size of the neck bone from front to back made a difference in the size of the spinal canal.

Three risk factors for cervical myelopathy have been identified in the Japanese population. These are male sex, narrow spinal canal, and large bone size. For men, the size of the bone is linked to the size of the spinal canal. This is called the canal/body ratio. The canal/body ratio of the cervical spine is smaller in Japanese men than in women, which may be why cervical myelopathy shows up more in Japanese men.

Sinsuke Hukuda, MD, PhD, and Yasuji Kojima, MD, PhD. Sex Discrepancy in the Canal/Body Ratio of the Cervical Spine Implicating the Prevalence of Cervical Myelopathy in Men. In Spine. February 1, 2002. Vol. 27. No. 3. Pp. 250-253.

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