Modular Prosthetic-limb System

Modular prosthetic-limb system, prototype. Stuart D. Harshbarger (American, b. 1964), Johns Hopkins University Applied Physics Laboratory and Orthocare Innovations, Thomas Van Doren (American, b. 1966), HDT Engineering Services, Richard Weir (American, b. 1960), Rehabilitation Institute of Chicago, and John D. Bigelow (American, b. 1957), Johns Hopkins University Applied Physics Laboratory; additional designers: Robert Armiger, James Beaty, Michael Bridges, James Burck, Michelle Chen, Steven Clark, Chad Dize, Harry Eaton, Eric Faulring, Michael Goldfarb, Ezra Johnson, Matthew Kozlowski, Niranjan Kumar, Lonnie Love, Courtney Leigh Moran, Tom Moyer, Aseem Raval, Julio Santos-Munne, Grace Tran, Matthew Van Doren, R. Jacob Vogelstein, Douglas Wenstrand, Michael Zeher. Manufactured by Johns Hopkins University Applied Physics Laboratory, HDT Engineering Services, and Orthocare Innovations. United States, 2009–present. Aluminum alloys, plastic, carbon-fiber composites, machined metals, electronic components. Courtesy of designers

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The design and function of prosthetic arms have lagged behind lower-limb prostheses, not evolving much beyond simple hook-and-cable technologies. But with greater numbers of U.S. soldiers returning from Iraq and Afghanistan with missing limbs (fatalities were down thanks to improved armor and medical care), the U.S. Defense Advanced Research Projects Agency sponsored the Revolutionizing Prosthetics 2009 program, aimed at developing a fully articulated, neutrally integrated artificial arm. Dubbed by the media as the “Manhattan Project for Prosthetic Limbs,” it consists of a multidisciplinary team from more than thirty organizations across the United States, Canada, and Europe, led by the Johns Hopkins University Applied Physics Laboratory.

The Modular Prosthetic Limb System is the team’s latest bionic-arm prototype. Made of lightweight carbon fiber and high-strength alloys, the arm has twenty-five degrees of freedom, or joint motions (the human arm has about thirty), closely mimicking the speed and dexterity of a natural limb. A wide range of neural integration strategies are being tested to control the arm and restore sensory feedback, from injectable myoelectric sensors—wireless devices the size of a grain of rice implanted in muscles of the remaining limb, which integrate directly with the nervous system to transmit signals instructing the prosthetic’s movement—to more near-term methods such as targeted muscle reinnervation, which allow for “thought controlled” prostheses. This approach reroutes nerves that once controlled the lost limb to unused muscles nearby, sometimes using chest muscles; when the brain tells the arm to move, the rerouted nerves create a contraction that provides an electrical signal interpreted by the prosthetic limb, making it move in a natural manner. The prototype is modular and configurable to a patient’s injury, and cosmeses, or skin coverings, feature simulated pores and hair to mimic the natural appearance of the native limb.