Upper Extremity Prostheses Gain Greater Realism

by James Cavuoto, editor

October 2014 issue

The potential market for upper-extremity neuroprosthetics continues to look promising and two recent developments in the U.S. and Europe have addressed critical issues amputees have faced with existing devices. These include difficulty in donning, doffing, and controlling a motorized prosthetic and the lack of sensory input needed for performing tasks requiring the dexterity of a natural arm.

In Europe, a team from Sahlgrenska University and Chalmers University of Technology has used ossointegration to seamlessly integrate a neural-controlled robotic arm with the user’s body. In the U.S., a team from Case Western Reserve University has demonstrated a prosthetic arm that restores the sense of touch to amputees. The combination of these two technologies could revolutionize the prosthetics industry in the years ahead.

Dustin Tyler and his colleagues at CWRU and the Louis Stokes Cleveland Veterans Affairs Medical Center used their system in two amputees who reported feeling sensations that were familiar and were able to control their prosthetic hands with more dexterity.

“The sense of touch is one of the ways we interact with objects around us,” said Tyler, “Our goal is not just to restore function, but to build a reconnection to the world. This is long-lasting, chronic restoration of sensation over multiple points across the hand. Our work reactivates areas of the brain that produce the sense of touch,”

How the system works and the study’s results were published online in the journal Science Translational Medicine. Tyler also described his work at the recent Neurotech Leaders Forum in San Francisco. Other research teams have attempted to use electrical stimulation to restore feeling. But the Cleveland team’s efforts are unique in several respects. First, the nerves used to relay the sense of touch to the brain are stimulated by contact points on cuffs that encircle major nerve bundles in the arm, not by electrodes inserted through the protective nerve membranes.

Surgeons Michael Keith and J. Robert Anderson from Case Western Reserve School of Medicine and Cleveland VA implanted three electrode cuffs in one user’s forearm, enabling him to feel 19 distinct points. They implanted two cuffs in another user’s upper arm, enabling him to feel 16 distinct locations.

The research team has developed algorithms that convert input from sensors taped to a patient’s hand into varying patterns and intensities of electrical signals that produce a more natural and repeatable sensation. The different signal patterns, passed through the cuffs, are read as different stimuli by the brain. The system has worked for two and a half years in one user and one and a half in the other. Other research has reported sensation lasting one month and, in some cases, the ability to feel began to fade over weeks.

Meanwhile, robotic prostheses controlled via implanted neuromuscular interfaces have become a clinical reality in Europe. Last year, a Swedish arm amputee was the first person in the world to receive a prosthesis with a direct connection to bone, nerves and muscles. An article about this achievement and its long-term stability was published in Science Translational Medicine.

“Going beyond the lab to allow the patient to face real-world challenges is the main contribution of this work,” said Max Ortiz Catalan, research scientist at Chalmers University of Technology and lead author of the publication. “We have used osseointegration to create a long-term stable fusion between man and machine, where we have integrated them at different levels. The artificial arm is directly attached to the skeleton, thus providing mechanical stability. Then the human’s biological control system, that is nerves and muscles, is also interfaced to the machine’s control system via neuromuscular electrodes. This creates an intimate union between the body and the machine; between biology and mechatronics.” The direct skeletal attachment is created by osseointegration, a technology in limb prostheses pioneered by associate professor Rickard Brånemark and his colleagues at Sahlgrenska University Hospital.

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