A new prosthesis allows leg amputees to adapt to all types of terrain.
- A new type of prosthesis was tested on seven people who had had their leg amputated below the knee.
- This device allowed them to walk at the same speed as able-bodied people.
- This also gave them access to all types of terrain.
A new robotic ankle has significantly improved the mobility of people who have had a leg amputated.
After just two training sessions (about six hours in total), seven individuals who participated in a small clinical trial testing the new device were able to walk as fast as able-bodied people. Another significant advance: the movements of their bionic joints perfectly imitated the natural movements of the ankle, which allowed them to move on all types of terrain.
Prosthesis: walking is a complex process
To understand the significance of this breakthrough, one must realize that walking is a much more complex process than it appears.
When you decide to take a step, your brain first sends signals down your spinal cord and into your legs, telling your muscles to contract, causing your joints to bend. The movement and position of each joint is then controlled by the contrasting action of two types of muscles: agonists and antagonists.
Then, when you contract your leg muscles to walk, you bend your hip, knee and ankle joints. The position of each of these joints at the beginning and end of the step are then different depending on the situation (rough terrain, slopes, mud, etc.).
Leg amputees have lost much of their muscle, as well as the nerves that control muscle contraction and send information about how the movement is going. Prosthetics research has long been trying to restore all of these commands and information.
New leg prosthesis: what’s new?
With early prosthetics, patients could control their replacement limb using a body-powered harness. For example, they learned to move their shoulder to control their prosthetic hand.
Later, more sophisticated prosthetics appeared. These use electrical signals in the muscles of the upper leg to direct movements of the ankle joint.
Finally, the new type of prosthesis mentioned at the beginning of the article uses the agonist-antagonist myoneural interface (AMI). The AMI restores signaling by reconnecting the agonist and antagonist muscles. The brain and the device can then read the complementary tension of the two muscles, as we do with our biceps and triceps.
The first prosthesis of this type is a bionic ankle for below-knee amputees, where the shin and calf muscles can be reattached. Since the agonist and antagonist are reconnected, the flexion of the joints can be read by the opposing tension of the two muscles. This tension adapts to different situations, such as sloping terrain and stairs, for example.
Finally, a decoder in the prosthesis can dynamically adjust ankle flexion as an intact limb would.
