[Image courtesy of the researchers]
During surgery, paired thigh muscles are rejoined using an agonist-antagonist myoneuronal interface (AMI), preserving the push-pull relationship that lets the nervous system sense limb position. Surgeons then anchor a titanium rod, called e-OPRA, inside the residual femur. The implant carries 16 wires that transmit muscle signals to a controller, which powers the knee in real time.
In a study, two amputees received the complete osseointegrated mechanoneural prosthesis (OMP). Eight others had the AMI surgery without the bone implant, and seven used standard socket limbs. All participants tested the same powered knee prototype.
“All parts work together to better get information into and out of the body and better interface mechanically with the device,” said the study’s lead author Tony Shu. “We’re directly loading the skeleton, which is the part of the body that’s supposed to be loaded, as opposed to using sockets, which is uncomfortable and can lead to frequent skin infections.”
OMP users bent the knee to target angles more accurately, climbed stairs more smoothly and cleared obstacles more reliably than the other groups. They also reported a stronger sense that the device was part of their body.
“A prosthesis that’s tissue-integrated — anchored to the bone and directly controlled by the nervous system — is not merely a lifeless, separate device, but rather a system that is carefully integrated into human physiology, offering a greater level of prosthetic embodiment. It’s not simply a tool that the human employs, but rather an integral part of self,” said senior author Hugh Herr, co-director of the K. Lisa Yang Center for Bionics at MIT.
Herr’s research team said the AMI procedure is already routine for below-knee amputations at Brigham and Women’s Hospital and could become standard for above-knee cases. Larger clinical trials are planned to seek U.S. regulatory clearance for the combined OMP system, a process the researchers estimate could take about five years.
“This paper represents the fulfillment of a vision that the scientific community has had for a long time — the implementation and demonstration of a fully physiologically integrated, volitionally controlled robotic leg,” said Michael Goldfarb, a professor of mechanical engineering and director of the Center for Intelligent Mechatronics at Vanderbilt University, who was not involved in the research. “This is really difficult work, and the authors deserve tremendous credit for their efforts in realizing such a challenging goal.”
The study was funded by the Yang Tan Collective and the U.S. Defense Advanced Research Projects Agency.
