In the meantime, high-tech prostheses allow complex movements to be performed. However, they require a lot of practice.
Everything can happen very quickly. A thoughtless act of a teenager, homemade fireworks – and the hand was gone. “Today, of course, I touch my head, but it’s like that, and you can’t undo it,” says Alexander Kühnle soberly. “I have still had luck in misfortune.
The now 59-year-old software developer has since worn a hand prosthesis that attaches to the wrist. To be more precise, he has two different prostheses: For heavy work and driving, he uses a system hand that is not very flexible but robust. That’s just the thing, for example, to hold a steering wheel. However, he usually wears his “iLimb Ultra Revolution”, a myoelectric prosthesis. This makes it one of the most frequently used types.
Myoelectric prostheses communicate with sensors on the residual limb that recognize muscle signals and control electric motors in the prosthesis. The wearer moves the prosthesis by consciously tightening the flexor or extensor muscle in the arm. In this way the hand can be opened and closed.
However, prostheses such as those by Alexander Kühnle can do even more: they have motors in the individual fingers and thus perform more complicated grips. This works through control programs. Alexander Kühnle can choose from 4 handles at any time. If he wants other combinations, he can switch to other grips via an app in his iPhone.
Don’t leave patients alone with technology
But he rarely does, because he usually gets along well with the 4 standard grips. Switching between the individual grips works well for him. “I am a computer scientist and understand how it works,” he says. “You also have to get a feeling for it and train.
However, Merkur Alimusaj, head of Technical Orthopaedics at the University Hospital in Heidelberg, says that for some patients this is a major challenge. “When patients understand and learn how to use the prosthesis, it has a great benefit in everyday life. If they are left alone with the technology, they cannot do anything with it”. Education and training are therefore essential.
Alexander Kühnle, computer scientist
“It doesn’t replace the real hand, but it works fine.”
Alexander Kühnle also used a week of ergotherapy to familiarise himself with his myoelectric prosthesis. How quickly patients can safely handle the new limbs is very individual. Once you have mastered the basic techniques, the main thing is to use them in everyday life. There is more to consider than one might initially imagine.
Many situations do not even catch the eye of a person with two functioning arms. The fact that you bend your arm when you squat usually happens automatically. Armprosthesis wearers, on the other hand, have to think about it actively.
Movements need more attention
Whether this works out well also depends on how often you actually use the prosthesis. For Alexander Kühnle it is only natural to spend almost the whole day with his artificial hand, especially in the shop or when he is out and about. “I simply see it as a useful tool,” he says. “It doesn’t replace the real hand, but it works well.”
Alexander Kühnle has been living with the prosthesis for a long time and is calm about it. For other patients, however, there is sometimes more behind it than just a tool. Even a visit to a restaurant with friends or going shopping can be mentally and physically stressful for the patients. The prosthesis ensures that the patient is not immediately noticed and also facilitates certain actions, depending on the model.
The prosthesis also has another function. “If, for example, the arm is missing on one side, the counterweight is missing,” says Merkur Alimusaj. “In patients, we can see that the musculature decreases over the years.” The spinal column can then bend, especially during more extensive amputations. Prostheses compensate for this.
Both in posture and in conscious and unconscious movements, a sense called proprioception plays an important role: the feeling of one’s own body, its position, its position in the environment, and the posture of the body parts to each other. Exactly this feeling is missing in prosthesis hands and arms. The wearer can move the prosthesis through his muscle signals. But he does not get any feedback, so he has to look to know what he is doing. Pressure, the procurement of the surface, the position of the fingers, we normally feel all this instinctively. If this information is missing, you need much more attention for each movement.
Passing on information to the body still a dream of the future
Scientists and doctors are trying to develop new methods. Alexander Kühnle finds the research exciting. He would be particularly pleased if the fingers could be controlled individually. But he knows that these technologies are still in their infancy.
One approach for more precise control is an operation known as Targeted Muscle Reinnervation (TMR). In this process, nerves in the arm that used to be linked to muscles in the missing hand, for example, are transferred to existing M