While prosthetic devices can restore mobility in lower limb amputees, the current state of the art suffers from numerous limitations. Standard prosthetics do not provide any useful feedback to the user, leading to poor mobility, high risk of falls, and in some cases, abandonment of the prosthesis. A new collaborative study from various European institutes shows promising preliminary results from three upper-leg amputees suggesting that adding in sensory feedback to prosthetic devices could dramatically improve functionality.

During walking, legs send a variety of sensory information to the brain, where it is used to adjust motion to avoid obstacles, climb stairs, or change direction. This sensory information includes touch and pressure on the foot and leg, vibration, and the stretch of muscles. By placing pressure sensors on the foot of a prosthetic device and an additional sensor which measures the angle of the knee, the neuroengineers were able to extract important sensory information from the prosthetic. The next challenge was to figure out how to give this information to the nervous system. The scientists surgically implanted devices which could send electrical signals to the sciatic nerve (the main source of sensory information from the legs) and found the proper conditions to mimic normal sensations of pressure or muscle contraction. Using a custom software interface, the information from the sensors was “translated” into the language of the nervous system and delivered to the brain in real time.

To test the effectiveness of their design, this interface was implanted in three amputees who completed stair climbing, obstacle avoidance, and straight-line walking tasks. Restoring feedback from the foot and knee improved the speed of motion, reduced the rate of falls, and improved agility in all participants. Additionally, the amputees were able to more effectively concentrate on a hearing task while walking when feedback was present than without it, suggesting the prosthetic is more naturally integrated and requires less continuous mental effort to operate.

These results are quite preliminary, having only been obtained from three participants, and so a larger number is necessary to confirm the potential improvements. Still, even limited sensory feedback showed substantial benefits and volunteers did not require any special training to use the prosthetics, suggesting that sensory-integrated devices are a promising next step in restoring mobility to amputees.

Managing Correspondent: Andrew T. Sullivan

Press Articles: Amputees merge with their bionic leg, Science Daily

Bionic Legs With Sensory Feedback Blur the Line Between Biology and Technology, Technology Networks

The bionic leg that promises to fully ‘merge man with machine’, The Telegraph

Original Journal Article: Enhancing functional abilities and cognitive integration of the lower limb prosthesis,” Science Translational Medicine

Image Credit: GollyGforce, Flickr, Under Creative Commons Attribution 2.0 Generic License

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