Good News for Amputees From Biomedical Engineers

This week, news came out in the Institute of Electrical and Electronics Engineers (IEEE) general publication Spectrum about improvements in quality of life for leg amputees by incorporating sensation into prosthetic legs.  H/T to A Large Regular in his links for yesterday, Sept. 12.

Luke Skywalker inspired a generation of prosthetic arms, including hands that grip, feel, and respond to thoughts.

This morning, an international team of researchers led by ETH Zurich announced a bionic leg that brings similar advances to the lower body. The prosthesis sends sensor input from the foot and knee to a nerve in an amputee’s thigh, allowing users to feel the bending of the knee, as well as pressure and vibrations of the foot on the ground. And those sensations, it turns out, make a big difference to the health of the wearer.

In its first two users, the bionic prosthesis improved walking performance, boosted endurance, and reduced phantom limb pain—the feeling of having a missing limb still attached, but in a wrong or painful position.

The team began with a commercially available prosthetic from Össur, which included a microprocessor and an angle sensor in the knee joint, and added an insole with seven sensors to the foot. The modified system then transmitted the foot and knee signals in real-time, via Bluetooth, to a controller strapped to the user’s ankle.  In the controller, an algorithm encoded the sensor signals into neural signals, then delivered them to the nervous system via a small implant in the patient’s tibial nerve, located in the back of the thigh.  The patients required very little training and said the sensations felt “very natural.”

The device was tested in two above-knee amputees, who had experienced the most severe form of lower-limb amputation. In a series of trials, scientists asked them to walk indoors and outdoors on various types of terrain—for example, in a large, sandy area—with and without the sensory feedback turned on.

When the users could feel the prosthetic limb, they walked faster, felt more confident, and consumed less oxygen, suggesting moving around was less strenuous than with a traditional prosthesis.

That last paragraph is interesting.  It says using the commonly used prosthetics with no feedback  sensations is more tiring because of the lack of those feedback signals the body is trained for and expects.  Here's where it gets even more interesting to me. Even though prior studies have shown that having that neural feedback reduces phantom limb pain in arm or hand amputees, that had not been demonstrated in leg amputees until this study. 

With just a few minutes of electrical stimulation per day, one patient experienced a complete loss of pain. In the other, pain was reduced about 80 percent, said co-author Francesco Petrini, also of ETH Zurich. Yet the two volunteers had to be present in the lab connected to an external device by a cable to undergo treatment, so current use of the system for pain relief is limited.

The benefits of walking faster, feeling more confident, expending less energy to walk, and reducing pain by feeding back mechanical sensations from the prosthetic leg to the body makes it seem like a no-brainer that this research should go on.  Our bodies are clearly designed to function with those sensations, if taking them away causes pain, and that says that patients should get limbs with this technology as early in their recovery as possible.  The problem is that they don't exist yet. 

ETH Zurich's Dr. Petrini says, “We are working to develop a fully implantable system which will be able to be maintained inside the body of the patients,” like a pacemaker.  Once that system is developed, they will run a larger controlled trial with 60 patients.

Now, in my view, the ultimate answer is tissue engineering to regrow those limbs, so that lost limbs are regrown similar to how primitive vertebrates like the axolotl regrow lost limbs.  People who follow this technology speculate that regenerated/regrown hearts are probably in the range of 10 years away.  There are more types of tissue in a leg than a heart, so they're more complex, but if you're perhaps 40 or younger, you might see legs being regrown in your lifetime. 

One of the types of Össur legs as used in the study; not one of the two initial patients from the experiment.  Photo source.