In order for an artificial leg to be better repaired by a person, it must receive more impulses from the muscles remaining after amputation.
When we bend our leg or arm, some muscles contract, while others, on the contrary, stretch. When we straighten our leg or arm, the same muscles change roles: those that stretched now contract, and those that contracted stretch. At the same time, information about the state of the muscles is constantly sent to the brain, thanks to which we feel our own movements, their speed and direction. And therefore, we can always influence the work of the muscles when we need, for example, to climb the stairs or just a slope. In fact, we do not even think about what and how we need to do with the muscles, everything happens automatically, the brain and nerves do everything themselves with minimal participation of consciousness.
If, however, instead of a regular leg with muscles, a bionic robotic prosthesis appears, then problems begin. In such a prosthesis, the artificial foot is movably attached using an analogue of the ankle joint, but its movements are controlled mainly by a program that switches the prosthesis between different walking modes. The bionic leg is connected to the body in such a way as to receive signals from living muscles, but these signals do not allow the gait to be sufficiently smooth and natural. After amputation, the brain no longer receives signals about the state of the muscles – it simply has nowhere to receive them from, the muscles, if they remain, are in a truncated version, and communication between them is almost completely reduced to nothing. Accordingly, in the opposite direction, from the brain to the remaining muscles, there are also much fewer signals. Therefore, the bionic leg has to be guided by autonomous programs and pressure sensors.
In the article in Nature Medicine employees Massachusetts Institute of Technology describe a method that makes the movements of a bionic leg more natural. Fourteen people who had their legs amputated below the knee took part in the study. Seven of them underwent a special operation before receiving a prosthesis: the remains of the muscles that had previously worked to bend and straighten the leg were preserved at the amputation site, and these remains were connected so that they could feel each other again. Feeling mutual tension and relaxation, the muscle fibers worked as if they controlled a real leg. They began to generate more neuromuscular impulses, which can be used to understand the position of the imaginary leg in space, walking speed, etc. These impulses were received by the bionic leg with its bionic ankle joint (the bionic leg itself, by the way, weighed 2.75 kg, which is quite comparable to the weight of an ordinary “live” leg).
The remaining seven participants in the experiment did not undergo such an operation, that is, the artificial limb was attached to the amputation site in the old way. And if those whose leg was attached in the old way received only 0.7 muscle impulses per second, then those whose leg was attached in the new way received as many as 10.5 impulses per second. And although in a normal leg the partner muscles generate about 60 impulses per second, these 10.5 impulses still made the movements much more natural. Those whose leg was attached in the new way walked 41% faster, their prosthesis adapted faster to stairs and walking on an inclined surface. In general, a person received more control over the new leg: the gait changed not depending on the pressure sensors and preset settings in the leg, but according to the will of its owner.
Testing a bionic leg that receives more muscle signals. (Illustration: H. Song et al., Nature Medicine, 2024)
It can be assumed that this approach can be used only in cases where the amputation was carried out in a certain way and in a certain place. However, the method certainly has room for improvement. At the end of last year, we wrote about a bionic hand prosthesis that faces the same problem: it needs clear signals from the muscles remaining after the amputation, and the signals are either lacking or difficult to interpret. In the case of the hand, the researchers found a solution by adding pieces of muscle from the patient’s thigh to the amputation site, and these pieces became signal translators between the nerves and the mechanical hand.
Source: www.nkj.ru
