A mind-controlled prosthetic arm could revolutionize movement for amputees.
The robotic arm attaches to an implant inserted directly into the bone at the end of the remaining part of the limb, and nerve reassignment surgery then allows brain signals to directly direct motion.
Researchers at Johns Hopkins University have been working with a test patient to perfect this technology – and today revealed he can move individual fingers and grasp small objects.
Johnny Matheny lost his arm to cancer in 2008, and has since pioneered the advancement of arm prosthetic technology.
The new system replaces the need for harnesses when working with the Modular Prosthetic Limb (MPL), which can be uncomfortable after prolonged wear.
For Matheny, it has helped to return many natural motions.
‘It’s all natural now,’ Matheny says after his first trial run using the MPL with the new implant.
‘Nothing is holding me down.
‘Before I had limited range; I couldn’t reach over my head and behind my back. Now—boom!—that limitation is gone.’
‘The [old harness system] does get a little uncomfortable after working with the MPL for a while,’ says Matheny, one of several patients who has helped scientists, engineers, and physicians fine tune the prosthetic’s capabilities and test its usability
Matheny was Johns Hopkins Hospital’s first patient to receive this treatment, as a part of the Revolutionizing Prosthetics program, a project funded by the Defense Department, and led by the Applied Physics Laboratory.
In order to make a prosthetic like the MPL work, a patient must first undergo targeted muscle reinnervation, which reassigns the nerves that controlled the arm or hand.
With osseointegration, a procedure that fixes a titanium implant into the marrow space of bone in the residual limb, researchers were able to overcome the complications that often occur at the socket.
An ill-fitting socket can lead to pain, sores, and blisters.
‘This accomplishment has eliminated one of the biggest gaps in prosthetic development: the socket,’ says Michael McLoughlin, chief engineer in APL’s Research and Exploratory Development Department.
‘Before, the only way I could put the prosthetic on was by this harness with suction and straps, but now, with osseointegration, the implant does away with all that,’ said Matheny after the MPL was attached.
At first, researchers planned to move forward cautiously after the MPL was attached to Matheny’s body by Richard McGough, chief of musculoskeletal oncology at the University of Pittsburgh Medical Center.
But, Matheny had done research and was prepared, allowing the exercises to launch right away.
‘He had configured a weighted attachment for the implant that was about 3 pounds, and he had been doing exercises on his own with this weighted implant, which really put us at a position to do more right from the get-go,’ says Courtney Moran, a clinical prosthetics who works closely with patients.
Along with individual finger control, the MPL gave Matheny the ability to move fingers simultaneously and grasp objects, and gave him two degrees of control at the wrist.
The achievement ‘moves the whole field forward, and not just a small step,’ McLoughlin says.
‘The challenge for us next is to really figure out how to get this technology out of the laboratory and into the hands of people that need it.’
As the work progresses, researchers aim to develop prosthetics with improved functionality for soldiers and civilian amputees.