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Science / Medicine : Wrist Shape May Reveal Susceptibility to Disorder : Anatomy: Researcher believes he has stumbled onto a crucial factor in why some people develop carpal tunnel syndrome and others do not.

February 19, 1990|REBECCA KOLBERG | Kolberg is a UPI science writer based in Washington, D.C

Take a good look at your wrists. Are they square or rectangular? One researcher thinks the shape may hold the answer to your risk of developing a painful and potentially disabling condition.

Carpal tunnel syndrome, caused by pressure on a nerve running through a "tunnel" formed by tiny wrist bones, typically strikes people who move their hands in quick, repetitive motions--from poultry pluckers to pianists.

Water buildup from pregnancy and nerve problems linked to an under-active thyroid or diabetes can also trigger the disorder, which can create severe pain and numbness in the hands.

But there must be more. While all people working a certain job move their hands in a similar fashion, only a relatively small fraction develop carpal tunnel syndrome.

In a three-year study of about 200 workers at a large automobile manufacturing plant in the Midwest, Dr. Ernest Johnson found nearly 80 workers complained of tingling, pain or other symptoms that might signal carpal tunnel syndrome.

Electrical tests showed that three-quarters of the 39 complaining workers with "square" wrists did indeed have nerve damage characteristic of carpal tunnel syndrome, while only a quarter of the 41 workers with "rectangular" wrists tested positive for nerve damage.

Johnson's team defined a square wrist as one nearly as thick as it is wide. Rectangular wrists--the most common type, according to Johnson--are substantially wider than they are thick.

The Ohio State study, published in the American Journal of Physical Medicine and Rehabilitation, follows up on Johnson's earlier observations that pregnant women suffering from carpal tunnel syndrome often had square wrists.

Other unpublished findings, also based on a recent study of auto plant workers, showed 99 of 100 people found to have "square" wrists at their time of employment went on to develop carpal tunnel syndrome, Johnson said.

The Ohio State researcher has not specifically looked at the mechanism underlying wrist shape's possible link to carpal tunnel syndrome.

Johns Hopkins University researchers in Baltimore say their study of 15 people uncovered no link between wrist shape and the amount of room in the carpal tunnel encasing the median nerve.

"In our work, we did not find a correlation between external wrist diameter and internal size of the canal," said Dr. Margit Bleecker, an associate professor of neurology. She said the only way to determine the size of the carpal tunnel is to "look" inside the wrist with sophisticated techniques like computerized axial tomography or magnetic resonance imaging.

But Johnson argues that the arrangement of tendons within the wrist may be more important in determining risk for the disorder than actual dimensions of the carpal tunnel.

The Ohio State doctor speculated that the way tendons are laid out in square wrists, as contrasted with rectangular wrists, may put greater pressure on the median nerve.

The exact distribution of wrist shapes in the population is unknown, Johnson said. But in his experience, the researcher has found more women appear to have square wrists than men, fitting in with the fact that more females are afflicted with carpal tunnel syndrome.

To those interested in determining their wrist shape, Johnson advises buying a caliper at a drafting or medical supply store.

Use the caliper to measure both width and height at the crease closest to the palm, and then divide the thickness measurement by the width. A ratio of 0.7 or higher indicates a square wrist--and possibly an increased risk for carpal tunnel syndrome, Johnson said.

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