This Prosthetic Leg with Sensory Feedback Can Improve Mobility
Would you wear a prosthetic leg that provides sensory feedback? If yes, you may only need to wait a few more years. A breakthrough bionic prosthetic leg was unveiled on September 9 by researchers from Switzerland’s Swiss Federal Institute of Technology. The artificial limb makes it possible for above-the-knee (AK) amputees to “feel” their leg, which results in greater stamina, stability, and mobility.
Image courtesy of AFP.
This ability to feel is made possible by surgically connecting sensors on a mechanical limb to nerve endings in the thighs, via electrode implants. Scientists from the University of Freiburg developed the electrodes while the prosthesis was from prosthetic manufacturer Össur. The researchers tested the device on two volunteers, both above-knee amputees.
Taking cues from neural feedback
The inspiration for this new prosthetic leg is the feedback loop that occurs between a biological leg and the brain. Nerves in the feet and legs relay a steady stream of electrical impulses to the brain. This feedback allows the brain to make instant adjustments to prevent falling on a steep slope or prevent leg fatigue by changing the amount of force.
In contrast, prosthetic users today don’t have that feedback loop, which makes it difficult to walk steadily. With the current prosthetic technology, prosthetic users resort to relying on their sound side leg, which causes them to tire faster.
To restore that feedback loop, researchers placed sensors under the soles of the prosthetic foot as well as around the joint of an electronic knee. Meanwhile, doctors surgically implanted electrodes into the volunteers’ thighs, which took the place of the nerve endings that had once sent and received messages from the amputated leg.
Better mobility, reduced phantom pain
Within three months, volunteers were able to test their bionic prosthesis. Both agreed that the machine allowed them to adjust their gait when walking. This was tested as they walked over sand, an uneven and soft surface. They also said that the leg allowed them to walk considerably faster than on a regular modern prosthesis.
Another takeaway was that the bionic leg reduces or removes phantom pain. One of the volunteers usually feels pain on a phantom big toe, heel, ankle, and calf. This pain can be strong enough to wake him up at night. However, since he started testing the leg, he said he doesn’t feel any phantom pain at all.
The possible explanation for this phenomenon is that the sensors and electrodes—which are connected by wires that pass through the skin—partially restored the feedback loop. The stochastic entanglement theory explains how an interrupted feedback loop can result in phantom limb pain.
More tests required
According to the researchers, they still need to conduct more tests over an extended period before the technology could be made available to the market. The next step for this research is to develop a fully implantable system with wireless neuro-stimulation, which will eliminate the need for wires to pass through the skin.
Within the next four years, the researchers plan to hold large-scale clinical trials with neuroprosthetics company SensArs.
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