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Scientists Test Prototype for ‘Phantom Limb’ Control of Upper-Limb Prostheses

(Left) Global view of the experimental setup during one of the functional tasks of grasping an object (here, the foam tennis ball) and releasing it in the dedicated container, with the arm prosthesis controlled through the associated mobilization of the phantom limb. (Right) Photo of the setup being used with P2.

prototype, and are working with amputees who are wearing the prosthesis during testing. “While numerous limitations related to robustness of pattern recognition techniques and to the perturbations generated by actual wearing of the prosthesis remain to be solved, these preliminary results encourage further exploration and deeper understanding of the phenomenon of natural residual myoelectric activity related to phantom limb mobilization,” concluded the researchers, “since it could possibly be a viable option in some transhumeral amputees to extend their control abilities of functional upper-limb prosthetics with multiple active joints without undergoing muscular reinnervation surgery.”

Austrian First To Undergo Single-Operation Upper-Limb Osseointegration Procedure While many lower-limb amputees have completed osseointegration surgeries to receive implants for direct attachment of prostheses, the procedure is much less common among upper-limb amputees. Austria’s Edmund Rath recently became the first person to undergo a single operation to install a “click” prosthesis that the brain controls via signals on the missing hand. Austrian surgeons implanted a metal rod into the bone of Rath’s residual limb in May 2018; the operation was projected live during an industry congress in Vienna, Austria. The rod features an external accessory that can anchor a prosthesis to the bone in the upper part of the 10


arm. During the operation, surgeons also located nerves that had been previously used to control the hand and connected them to the muscles of the upper arm, a procedure called “reinventing the directed muscle.” It took six weeks for the implanted nerves to grow in the subject’s muscles to allow him to control six different functions of a robotic prosthetic arm, which was supplied by Ottobock. Since the surgery, Rath has been learning to complete increasingly difficult tasks. He said the implant allows him to move his arm freely, compared to the restricted movement provided by a socket. Rath displayed his new abilities using an osseointegrated prosthesis during an Ottobock Media Day in October.

IMAGE:© N. Jarrassé 2018

French researchers are studying phantom-mobility-based prosthesis control in transhumeral amputees without surgical reinnervation. A preliminary study, published in the November 29 issue of Frontiers in Bioengineering and Biotechnology, found that amputee subjects could be trained to control their prostheses based on phantom limb mobilization and myoelectric pattern recognition techniques. Researchers from the French National Center for Scientific Research (CNRS) and Aix-Marseille University developed a natural approach to prosthesis control stemming from the idea that many amputees can voluntarily move their “phantom,” or missing, limb. Previous studies had found that some arm amputees are able to engage in muscle contractions in the residual limb that would allow for finger pinching, making a fist, or rotating the wrist—contractions that are not connected with the joints used prior to amputation. Building upon this phenomenon, the researchers, led by Nathanael Jarrasse, PhD, and Jozina de Graaf, developed a prototype using algorithms capable of recognizing muscle activity generated by mobilization of the phantom limb and reproduction of the detected movement by the prosthesis, via “intuitive control.” Two amputee subjects tested the prototype, using a prosthesis placed near—but not attached to—the residual limb. After several minutes of acclimating to the system, both participants achieved the goal of controlling the prosthesis to perform specific grasping and releasing tasks. The researchers are performing additional testing of the

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January 2019 O&P Almanac  

American Orthotic & Prosthetic Association (AOPA) - January 2019 Issue - O&P Almanac

January 2019 O&P Almanac  

American Orthotic & Prosthetic Association (AOPA) - January 2019 Issue - O&P Almanac