The French Electric Hand: Some Observations And Conclusions
Luigi F. Lucaccini Peter K. Kaiser J. Lyman
Over the past decade the Vaduz or French electric hand has frequently been mentioned in the literature. The following abstract succinctly presents experiences at the University of California at Los Angeles with one model of this device. A full report is scheduled for publication in the Fall 1967 issue of the Bulletin of Prosthetic Research.
Two amputee wearers completed a series of seven performance tests with the French hand, with an APRL hand, and with the intact left hand. As would be expected, performance was found to be faster and more accurate with the normal left hand than with either prosthesis. Comparisons between the two prostheses alone failed to reveal significant differences in performance, with a few exceptions. The most notable of these was the thickness discrimination task. The electric hand was found to be seriously deficient in supplying (nonvisual) feedback about the amount of opening of the hand.
Overall, both amputees tended to perform slightly better with the conventional prosthesis than with the electric hand. The difference was larger for the experienced wearer (Subject 1) and can probably be attributed to his long experience with the conventional prosthesis. However, the differences were not statistically significant.
The maximum level of prehension force possible with the electric hand was sufficient only for light-duty tasks. Informal observations revealed that the amputee wearers were not able to turn handles or doorknobs easily with the hand, or to lift heavy objects. A maximum grasp force of 15 pounds (double that provided by the hand) has been recommended for terminal devices, although most activities require forces of 3 pounds or less.
Another drawback of the hand is the fact that the amputee has only two prehension forces available, which he selects by choosing to effect a gear change or not.
The hand was acceptable to both pilot wearers. They preferred its method of control to that of the cable-controlled APRL hand, even though one amputee used an unorthodox control movement. Subject 1 reported the control movement to be compatible with the normal neuromuscular control pattern. He stated that this was the first time since his amputation that a prosthesis had responded when he attempted to close his "phantom hand." Appearance, speed of motion, and the fact that the control motion was invisible were all given as acceptable features of the device. Neither amputee objected to the noise of operation, which was loud enough to attract attention to the wearer, particularly when changing gears.
The reliability of the French hand was found to be quite low, contradicting reported experiences of European wearers. Operating difficulties were traced to poor workmanship and quality of materials in the model tested, the difficulty of making adjustments to the hand, and the seeming inability of the hand to maintain a given level of adjustment.
No safety problems were encountered during the operation of the hand.
The hand was purchased from its developer at a cost of about $300. A Los Angeles orthopedic supply firm estimated that it would be possible to sell the hand in this country for about $600, including servicing.
In conclusion, the performance inadequacies of the electric hand (low grasp force, inability to vary grasp force, lack of feedback to amputee, and noisy operation), coupled with its high cost and low reliability, argue against adoption of the device by American amputees. The unique feature of the hand-its control system-was well received by both pilot wearers; they found it easy to operate, without fear of accidental activation. Implementation of improvements in the areas noted should make the French electric hand a valuable prosthetic device.