For the study, two participants with transradial amputations had RPNIs created by suturing skeletal muscle grafts to peripheral nerves or nerve fascicles in the residual limb. Intramuscular EMG (iEMG) electrodes were implanted into the RPNIs and muscles in the residual limb.
After the surgery, the participants’ functional performance was assessed in several ways, including through a multiple degrees-of-freedom control test called the Coffee Task (putting a cup and a coffee pod into a coffee machine, pushing the start button, moving the filled cup to a table, and opening a sugar packet and pouring it into the cup). Other tests involved controlling a virtual hand and wrist in real time by mimicking various on-screen grips, and a posture classification experiment, in which the subjects controlled hand or wrist movements of a virtual hand while sitting and standing. In each test, the participants achieved faster, more accurate and more reliable control using the implanted electrodes than the surface electrodes.
After comparing RPNIs and iEMG against conventional surface EMG, the researchers found that the ability to control wrist rotation reduced the users’ total body compensations, and the implanted electrodes significantly reduced task completion times and offered more accurate and stable control compared to surface electrodes when wrist rotation was added as an additional control movement.
In the article in Physics World, which has an international audience of physicists, scientists, and researchers, the study’s senior author, Cynthia Chestek, PhD, explained that RPNI grafts are also beneficial for the nerve itself. “They provide a target for nerve endings that prevent the formation of painful neuromas, and that may in turn help reduce phantom limb pain,” she said. “In future, it would also be possible to place electrodes and a wireless transmitter during that same surgery, such that no additional surgeries are required other than the original amputation.”
Chestek noted that in a previous study where participants wore a prosthesis without an active wrist, “almost everything we asked them to do required large body movements.
“Fortunately, the implantable electrodes provide highly specific and high-amplitude signals, such that we were able to add that wrist movement without losing the ability to classify multiple different grasps,” she said. “The next step would be to pursue continuous, rather than discrete, movement for all of the individual joints of the hand….”
To read “Implanted Electrodes Provide Intuitive Control of Prosthetic Hand,” visit Physics World.
To read the open-access study, “Regenerative peripheral nerve interfaces (RPNIs) and implanted electrodes improve online control of prostheses for hand and wrist,” visit the Journal of Neural Engineering.
To read more on the topic from The O&P EDGE, search for prosthetic control at opedge.com.
