Study Could Help Workers Avoid Carpal Tunnel

Ergonomics researchers from the University of California at San Francisco and McMaster University in Ontario have conducted a groundbreaking study that establishes limits on how much a wrist can be flexed before nerve damage sets in.

Researchers anticipate that their findings can be used to create simple guidelines to help workers avoid wrist postures that are likely to cause nerve trauma, which can lead to carpal tunnel syndrome.

After analyzing the pressure placed on the nerve in the carpal tunnel of 37 healthy men and women between the ages of 22 and 50, researchers concluded that when sustained pressure on the carpal tunnel reaches 30 mmHG, injury is likely to occur.

The researchers recommend keeping the pressure below 30 mmHG. In order to do that:

  • Sustained wrist extension (bending the hand back) should not exceed 32.7 degrees.
  • Wrist flexion (bending the wrist toward the palm) should not exceed 48.6 degrees.
  • Ulnar deviation (sideways toward the small finger) should not exceed 14.5 degrees.
  • Radial deviation (sideways toward the thumb) should not exceed 21.8 degrees.

According to the researchers, a set of guidelines could be developed from their data – guidelines that could, if applied by engineers and designers during the design of work and tools, protect workers. Such guidelines also could be used to identify tasks that may put workers at risk for developing or aggravating CTS.

The findings of this study appear in the February issue of Human Factors: The Journal of the Human Factors and Ergonomics Society. The article can be downloaded at

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