Prostheses with feedback
A person can very well determine the position, speed of movement and rotation of his limbs even with his eyes closed. This sensation, known as proprioception, allows us to accurately control the movements of the body. Despite significant advances in the development of prosthetics in recent years, specialists have not yet been able to return this feeling to people with artificial limbs, the absence of which limits their ability to control their movements.
Researchers at the Massachusetts Institute of Technology (MIT), working under the leadership of Professor Hugh Herr, have invented a new electroneuron interface and a communication concept that allows sending commands from the central nervous system to robotic prostheses, providing proprioceptive feedback that provides the central nervous system with information about joint movements. This new concept, called the agonist-antagonist myoneuronic interface, implies the use of an innovative surgical approach to joint amputation, ensuring the preservation of dynamic intermuscular connections. Preclinical studies of the new concept were conducted at MIT, and a subsequent pilot clinical trial was conducted at Brigham and Women's Faulkner Hospital.
The new myoneuronic interface consists of two free muscle grafts placed subcutaneously on the surface of the fascia (muscle sheath).
Figure from the article by Srinivasan et al.
On prosthetic control: A regenerative agonist-antagonist myoneural interface (Science Robotics 2017).
The interface consists of two opposing muscle-tendon complexes, known as an agonist and an antagonist. These complexes are connected in series in such a way that when one of them is shortened and shortened by volitional or electrical stimulation, the second one stretches, and vice versa. Such paired movements allow natural biological sensors to transmit electrical signals to the central nervous system that carry information about the length of the muscle, as well as the speed and strength of its contractions. These signals are interpreted by the brain as a natural acceptance of the joint.
Professor Herr explains that this is how the mechanism of muscle-tendon proprioception works in human joints. Since muscles have their own nerves, when the described muscle interaction occurs, information is sent to the brain that ensures a person's ability to sense the movement and position of muscles, as well as the speed and strength of their work. With the help of electrodes connected to the interface, researchers can register the electrical signals emitted by the muscles or cause them to contract using electrical impulses. When a person thinks about what to move his non-existent ankle joint, the myoneuronic interface provides movement of the bionic prosthesis, in turn, sending signals to the brain. This allows a person to feel the movement of his prosthesis in the entire angular range.
For the first time in clinical practice, two agonist-antagonist myoneuronic interfaces were implanted in a patient during surgery for leg amputation below the knee. One of them was intended to control the work of the bionic ankle joint, and the second – the bionic hip joint.
After the operation, the prosthesis specially developed by MIT specialists was connected to the peripheral nerves of the patient using electrodes placed on top of each of the muscles of the myoneuronic interfaces. After that, the researchers compared the motor activity of a patient with implanted myoneuronic interfaces with the mobility of four patients who underwent traditional leg amputation surgery below the knee and used similar prostheses. Observations showed that the patient who underwent the experimental procedure had more stable control over the movements of the prosthesis and could move more efficiently compared to patients in the control group. In addition, the myoneuronic interface provided rapid manifestations of natural reflexive movements, such as stretching the foot in the direction of the next step when walking up the stairs.
After that, the authors implanted myoneuronic interfaces in 9 more patients with legs amputated below the knee and plan to adapt the procedure for patients requiring amputation of legs above the knee, as well as arms above and below the elbow.
Article by Tyler R. Clites et al. Proprioception from a neurologically controlled lower-extremity prosthesis is published in the journal Science Translational Medicine.
Evgenia Ryabtseva, portal "Eternal Youth" http://vechnayamolodost.ru based on the materials of Brigham and Women's Hospital: Surgical Technique Improves Sensation, Control of Prosthetic Limb.