Clippinger's Arm

With its movable, spring-loaded hooks, the prosthesis fitted onto the stump of Dan Aycock's left arm two years ago was a substantial improvement over the ugly iron claw of earlier days. But the artificial arm still had a serious deficiency. Because Aycock, 38, who lost his arm in a textile-mill accident, was unable to tell how much pressure he was exerting on anything he was trying to pick up or use, he risked breaking the gauges and other delicate items that he handled on the job in a Louisburg, N.C., automobile agency. Now Aycock's problem has been solved by a new development in prosthetics: an artificial arm with feeling.

For years, engineers have tried to overcome the insensitivity of the artificial arm with a variety of devices that produce electric shocks or emit auditory signals when pressure is put on the hooks. Dr. Frank Clippinger Jr., an orthopedist at Duke University Medical Center, tried a different approach. He coupled a strain gauge into the cable that operates the hook end of an artificial arm and wired it to a surgically implanted electrical stimulator. The stimulator, in turn, was connected directly to the medial or main arm nerve; the current is perceived as a mild tingling, which by its intensity tells the wearer how much force he is exerting.

The four patients who have already been fitted with the experimental prosthesis report that it feels and performs much more like a normal hand than earlier devices. Milton Williamson, 47, an elementary school principal, used to wear clip-on bow ties; using Clippinger's arm he can now tie his own.

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