Engineers at Case Western Reserve University in Cleveland, Ohio report in the Journal of Neural Engineering that implanted flat interface nerve electrodes (FINE) placed around the femoral nerve trunk can selectively stimulate each muscle the nerve innervates. Matthew Schiefer and others intraoperatively tested the muscles needed for a human to transition from sitting to standing and found that the FINE device could cause individual muscles to be strong enough. Dr. Schiefer and Dustin Tyler (the inventor of FINE) described the study to NewScientist.
From the article:
Motor nerves like this are in some ways like telephone cables: they are made up of electrically isolated bundles of nerve fibres, each one of which connects to certain groups of muscle cells. In the 2006 trial, electrodes were simply placed on the nerve’s surface using a spiral cuff, but this makes for a poor connection with fibre bundles close to the nerve’s core. The new solution, known as the flat interface nerve electrode (FINE), is a cuff that squashes a nerve flat to bring fibre bundles closer to the surface – and to the eight electrodes in the device’s soft rubber lining.
It makes for a much better connection, says Dustin Tyler, who invented the FINE and heads research into its effectiveness. “We apply a little bit of pressure to reshape the cross-section without damaging the nerve.”
Recent tests validated that approach. The cuff was temporarily implanted on the femoral nerves of seven patients undergoing routine thigh surgery. Pulses of current 250 microseconds long were used to selectively and independently activate the muscles that extend the knee and flex the hip joint when a person stands up. The pulses were not enough to bend the joints as much as they would when standing, but the results suggest that longer pulses should stimulate the muscles to provide enough force to support the body’s weight. Longer trials are being planned, subject to approval from the US Food and Drug Administration.
From the abstract in JNE:
In humans, we tested the hypothesis that a flat interface nerve electrode (FINE) placed around the femoral nerve trunk can selectively stimulate each muscle the nerve innervates. In a series of intraoperative trials during routine vascular surgeries, an eight-contact FINE was placed around the femoral nerve between the inguinal ligament and the first nerve branching point. The capability of the FINE to selectively recruit muscles innervated by the femoral nerve was assessed with electromyograms (EMGs) of the twitch responses to electrical stimulation. At least four of the six muscles innervated by the femoral nerve were independently and selectively recruited in all subjects. Of these, at least one muscle was a hip flexor and at least two were knee extensors. Results from the intraoperative experiments were used to estimate the potential for the electrode to restore knee extension and hip flexion through functional electrical stimulation. Normalized EMGs and biomechanical simulations were used to estimate joint moments and functional efficacy. Estimated knee extension moments exceed the threshold required for the sit-to-stand transition.
NewScientist: Paralysed limbs revived by hacking into nerves…
Full article in Journal of Neural Engineering: Selective stimulation of the human femoral nerve with a flat interface nerve electrode
NOTE: Please welcome Dan Buckland, our new editor, and the author of this post. Dan is an MD/PhD candidate at Harvard Medical School and the MIT Department of Aeronautics and Astronautics. His research focuses on ultrasound imaging of the cervical spine in extreme environments (NASA, DOD, etc…)