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Researcher Seeks New Ways to Detect Carpal Tunnel Syndrome

Industrial and Systems Engineering professor Robert G. Radwin wants to save workers' hands. Much of his research concentrates on understanding the mechanisms through which hands become injured through cumulative trauma, developing new biomedical instruments to detect hand injuries early on, and designing, selecting, installing and using industrial hand tools through ergonomics so that they prevent hand trauma.

Just figuring out when workers are at risk before a serious and costly injury develops can be tricky, Radwin says. Working with Dr. Arthur Rodriquez of the UW-Madison Clinical Sciences Center, Radwin is developing new medical instruments to improve the detection of one common hand injury: carpal tunnel syndrome. This numbing disorder--an entrapment of the median nerve in the wrist--is often known for its effects on computer users, but is prevalent among workers who perform numerous repetitive tasks.

Workplace injury research

Associate Professor Robert G. Radwin (left) uses electronic motion and force sensors and electrodes attached to an operator's hands and arms to help quanitify worker exposure to physical stress. (large image)

"Currently," Radwin says, "most screening tests for carpal tunnel syndrome are not very specific, accurate or practical for routinely monitoring workers. In fact, there are none that are very good at all." The clinical test for carpal tunnel syndrome is called electromyography. But it is expensive and time consuming, it must be performed by a physician and it is unpleasant to outright painful. In short, it's not practical as a routine monitoring test and not many people would be willing to take it with the kind of frequency required for early detection of repetitive motion injuries. "If a problem is detected early on, an ergonomics and medical intervention can be taken to prevent a long-term problem from occurring," he explains.

Radwin and his graduate students have developed two early-detection instruments that are no more difficult to administer than a common hearing test. And just as workers in a loud factory get periodic hearing checkups, these tests could be used for regular checkups of workers who are exposed to vibrations, forceful exertions, stressful postures and repetitive motions. In one test, workers run their fingers over a smooth metal plate that is split by a variable-width gap. As a computer varies the gap--which a micromanipulator can set from as small as 1/10th of a micron to several millimeters wide, the subjects respond when they can feel the defect in the plate. Because carpal tunnel syndrome dulls touch, suffers tend to feel only the wider gaps.

The other test is a simple video game that is controlled by squeezing bars together. "The patients we tested who have carpal tunnel syndrome use a lot more force than the people who don't have carpal tunnel syndrome symptoms and nerve-conduction deficits," Radwin explains. That's because the median nerve tells your brain how hard you are squeezing and sends motor signals to the muscles in your fingers and thumb. "If there's an injury to the median nerve, that transmission of the nerve signals to the brain and back to the fingers may be impaired."

Currently the researchers are conducting trials for both devices at UW hospital and they are about to expand to the workplace, using employees as volunteers. In the hospital study, both tests are good at detecting known carpal tunnel syndrome sufferers, who were identified using electromyography as the "gold standard." What isn't clear is whether the tests will help health care professionals ferret out the syndrome in its infancy. "Here's a test that's very simple to administer and is painless, and with which we can get very useful information," Radwin says. "But we don't yet know if the test can detect carpal tunnel syndrome in the early stages. That can only be learned from long-term studies conducted in the field."