Prosthetic legs help lower-limb amputees regain mobility. Fitting a patient with a prosthetic only starts the process. Patients then need to learn how to walk with a prosthetic, a period that is often physically and mentally exhausting. Our feet and legs provide feedback about motion, surfaces, temperature, impediments, and other factors. Most prosthetics lack the means to transmit sensory data back to the human brain, so re-learning to walk is harder because it lacks sensory feedback.

We have written about various technologies for adding sensation to upper limb prosthetics. A team at the University of Utah modified a prosthetic arm developed by DEKA Research & Development Corp with a sense of touch in a project funded by DARPA. Researchers from the University of Applied Sciences Upper Austria, developed a prosthetic-sensing wearable sock designed to wear over the foot of a prosthetic leg.

Engineers at ETH Zurich and Lausanne startup SensArs recently published a report in Nature that describes their work with sensory feedback restoration in leg amputees. The basics of the “feeling prosthetic” include tactile sensors attached to the sole of the prosthetic foot, knee movement data from movement sensors in the prosthetic’s electronic knee joint, and tiny electrodes connected to the volunteer patients’ residual leg nerves. The team developed algorithms that translate the data from the tactile and movement sensors into electrical pulses delivered to the residual nerves. The human brain finishes the process as it learns to recognize and respond to the pulses sent via the nervous system.

Two volunteer patients in the study wore the smart prosthetic and found that they re-learned to walk with much less effort and stress. The researchers compared oxygen consumption when adapting to the sensing prosthesis with adapting to a prosthetic leg without the sensory feedback. The researchers noted the patients with the smart prosthesis didn’t need to concentrate as hard on walking and were able to focus on other tasks. The study also found that neurostimulation from the prosthesis reduced phantom pain in both volunteers; in one case phantom pain ceased totally.

The ETH work showed that enlisting the human brain in the re-training process in a natural manner (responding to nerve stimuli) has the potential to speed and ease the process.