The prosthetic arm has a tradition that dates back to the Middle Ages. Since the World Wars, there have been independently movable prosthetic arms in addition to jewelry arms. In modern times, myoelectric prostheses can be moved lifelike via muscle tension in the arm stump.
What is a prosthetic arm?
Prosthetic arms visually replace the missing arm, creating an image of integrity and symmetry. A prosthetic arm is used for cosmetic and functional replacement of the upper extremities. The history of prosthetics dates back to the Egyptians. Thus, even before Christ, there were smaller prostheses to replace lost toes. The beginnings of arm prosthetics can be traced to the Middle Ages. In the 16th century, for example, there were the first iron hands made of metal materials that met both cosmetic and functional requirements. The individual joints of the iron hands were still passive at that time and had to be bent and sprung open with the help of the healthy hand. In the 20th century, arm prostheses for war-damaged persons became increasingly relevant. A major breakthrough was the Sauerbruch arm, developed at this time by the surgeon Sauerbruch. Jakob Hüfner further developed the Sauerbruch arm and the first actively movable arm prostheses were born. During the Second World War, Lebsche worked successfully on the Sauerbruch idea. Present-day myoelectric arm prostheses are also based on the functional principle of the Sauerbruch arm. To be distinguished from prostheses are epitheses, which serve purely aesthetic purposes.
Forms, types and styles
In the 21st century, prosthetic arms can be divided into decorative arms and working arms. Decorative arms serve only aesthetic purposes. They visually replace the missing arm, creating an image of integrity and symmetry. Much more expensive than jewelry arms are myoelectric working arms, which can be actively moved using the patient’s own muscle tension at the prosthetic attachment. With some practice, this enables voluntary grasping and opening as well as voluntary stretching and bending. Nowadays, myoelectric arm prostheses are also well developed in terms of aesthetics. For a long time, only leather was put over the metal prostheses. Today, the outer skin is made of either PVC or silicone. Currently, the most expensive variant is silicone covers that contain nylon reinforcement. These arms are strong, stain-resistant, tear-resistant and relatively resistant to abrasion. As a rule, a silicone cover with nylon reinforcement must be changed every six months. In addition to forearm prostheses, there are also upper arm prostheses in myoelectrics today. Hybrid prostheses are to be distinguished from these open implants. These closed implants do not replace a lost limb, but only a damaged joint and are completely surrounded by body tissue.
Structure and mode of operation
Today, the most advanced form of open arm prosthesis is the myoelectric arm prosthesis. These prostheses are powered by a battery. Movement of the elements occurs through contraction of the muscles in the residual limb. Myoelectric prosthetic arms are controlled by a surface electrode. This electrode derives an electromyogram from the bioelectric muscle voltages in the microvolt range. Subsequently, a conversion into motor control signals takes place, whereby these control signals are tuned to the motor of the prosthesis. There is proportionality between the muscle force and the myogram. In simple terms, the number of all activated muscle fibers is relatively proportional to the applied force. The efficiency of myoelectric artificial arms depends on how many control signals can be used for sequential control. Ideally, the prosthesis wearer can still contract individual muscle groups in a targeted manner despite the amputation. The voltage of the individual muscles can be measured on the skin via electrodes and makes the individual prosthetic joints arbitrarily controllable. The first myoelectric artificial arm for commercial purposes existed during the 1960s in the USSR. The technique of myoelectric arms is based on the Sauerbruch arm in that Sauerbruch at that time incorporated a canal into the remaining muscle tissue of the arm stump. This channel contained a pin through which the muscle contraction of the arm stump could be transmitted to the prosthesis.
Medical and health benefits
Arm prostheses in the myoelectric form fulfill high health benefits.They restore an absolutely mobile limb that has been lost due to amputations, deformities or accidents and war injuries. This development was hardly imaginable until more than a century ago. Prostheses were equipped with metal joints even then, but were not actively mobile. Since the Sauerbruch arm, things have changed in prosthetics and prostheses are fulfilling an even greater medical benefit for an even greater number of people. Although the prices for myoelectric prostheses in particular are still relatively high and therefore not everyone can wear such a fully functional prosthesis, the fitting of a movable arm prosthesis has at least become safer since then. Indeed, while surgical complications and severe infections were still to be expected back then due to the pin design, the risk of infection is low with today’s systems. In addition to the functional benefits, modern arm prostheses offer psychological value above all. Many amputation patients are distressed by their different appearance. Some suffer from depression and find it difficult to cope with everyday life. Today’s relatively lifelike prosthetic arms give them back their security in social life. Jewelry arms with this purpose have a long tradition and were made centuries ago to provide psychological relief to amputation patients and facilitate their reintegration into social life. Nevertheless, for a long time decorative arms were conspicuous prostheses and hardly gave the impression of a real arm. Today, prosthetic arms can hardly be distinguished from real limbs from a distance.
