Artificial arms, not having to support the weight of the body, may be made of lighter metals and plastics. They are usually strapped to the trunk and controlled by a shoulder harness. Bionic arms have been developed that permit a person to use thought to control the limited movements of the motorized prosthesis. The commands are transmitted through chest muscle that has been surgically connected to the remaining nerves associated with the lost limb; electrodes linked to the artificial arm convert the sensed electrical signals of the muscle into arm movement. Tests with monkeys have shown that robotic arms can also be controlled by the brain's electrical signals directly, using probes implanted in the brain and computer software to interpret the signals.
Artificial hands vary in structure and utility; research and development has resulted in devices that are both cosmetic and functional. For example, an artificial hand has been devised that utilizes a split hook resembling a lobster claw; this is enclosed within a flexible plastic glove that can be made remarkably lifelike, even having fingerprints. The biceps muscle can be attached to the prosthesis by a surgical procedure called cineplasty, which permits grasping in the terminal device while dispensing with shoulder harnesses. A more recent artificial hand has separate motors for each finger, allowing for a more natural and useful grip and movement; the prosthesis is controlled by electrical signals generated by the arm muscles that normally control the hand.
An artificial limb is a type of prosthesis that replaces a missing extremity, such as arms or legs. The type of artificial limb used is determined largely by the extent of an amputation or loss and location of the missing extremity. Artificial limbs may be needed for a variety of reasons, including disease, accidents, and congenital defects. A congenital defect can create the need for an artificial limb when a person is born with a missing or damaged limb. Industrial, vehicular, and war related accidents are the leading cause of amputations in developing areas, such as large portions of Africa. In more developed areas, such as North America and Europe, disease is the leading cause of amputations. Cancer, infection and circulatory disease are the leading diseases that may lead to amputation.
An artificial limb is mythologically referred to in the Rigveda, the "iron leg" given to Vishpala by the Ashvins. The first specimen discovered archaeologically, known as the Roman Capua Leg, was found in a tomb in Capua, Italy, dating to 300 BC, and was made of copper and wood. Two artificial toes found on Egyptian mummies are even older, dating to 1295–664 BC; these are being tested (as of July 2007) to determine whether they could have been used in life. Armorers in the 15th and 16th centuries made artificial limbs out of iron for soldiers who lost limbs. Over the next several centuries, craftsmen began to develop artificial limbs from wood instead of metal because of the lighter weight of the material.
In the 19th century, artificial limbs became more widespread due to the large number of amputees from wars such as the Napoleonic Wars in Europe and the American Civil War. In the latter, a Confederate soldier, J.E. Hanger, who had himself suffered the war's first amputation (see Battle of Philippi) founded what was for a time the world's largest artificial limb factory.
Technology improved primarily for two reasons: the availability of government funding and the discovery of anesthetics. After World War II, the Artificial Limb Program was started in 1945 by the National Academy of Sciences. This program helped improve artificial limbs by promoting and coordinating scientific research on prosthetic devices.
In recent years, a great deal of emphasis has been placed on developing artificial limbs that look and move more like actual human limbs. Advances in biomechanical understanding, through the combined work of doctors and engineers, the development of new plastics, and the use of computer aided design and computer aided manufacturing have all contributed in the development of more realistic artificial limbs.
There are four main types of artificial limbs. These include the transtibial, transfemoral, transradial, and transhumeral prostheses. The type of prosthesis depends on what part of the limb is missing.
In addition to new materials, the use of electronics has become very common in artificial limbs. Myoelectric limbs, which control the limbs by converting muscle movements to electrical signals, have become much more common than cable operated limbs. Myoelectric limbs allow the amputees to more directly control the artificial limb. Computers are also used extensively in the manufacturing of limbs. Computer Aided Design and Computer Aided Manufacturing are often used to assist in the design and manufacture of artificial limbs.
Most modern artificial limbs are attached to the stump of the amputee by belts and cuffs or by suction. The stump usually fits into a socket on the prosthetic. The socket is custom made to create a better fit between the leg and the artificial limb, which helps reduce wear on the stump. The custom socket is created by taking a plaster cast of the stump and then making a mold from the plaster cast. Newer methods include laser guided measuring which can be input directly to a computer allowing for a more sophisticated design.
One of the biggest problems with the stump and socket attachment is that there is a large amount of rubbing between the stump and socket. This can be painful and can cause breakdown of tissue.
Artificial limbs are typically manufactured using the following steps:
Recently the i-Limb hand, invented in Edinburgh, Scotland, by David Gow has become the first commercially available hand prosthesis with five individually powered digits. The hand also possesses a manually rotatable thumb which is operated passively by the user and allows the hand to grip in precision, power and key grip modes. Raymond Edwards, Limbless Association Acting CEO, is the first amputee to be fitted with the i-LIMB by the National Health Service in the UK. The hand, manufactured by "Touch Bionics" of Scotland, went on sale on 18th July 2007 in Britain for £8,500 (U.S. $17,454).
Targeted muscle reinnervation (TMR) is a technique in which motor nerves which previously controlled muscles on an amputated limb are surgically rerouted such that they reinnervate a small region of a large, intact muscle, such as the pectoralis major. As a result, when a patient thinks about moving the thumb of his missing hand, a small area of muscle on his chest will contract instead. By placing sensors over the reinervated muscle, these contractions can be made to control movement of an appropriate part of the robotic prosthesis.
An emerging variant of this technique is called targeted sensory reinnervation (TSR). This procedure is similar to TMR, except that sensory nerves are surgically rerouted to skin on the chest, rather than motor nerves rerouted to muscle. The patient then feels any sensory stimulus on that area of the chest, such as pressure or temperature, as if it were occurring on the area of the amputated limb which the nerve originally innervated. In the future, artificial limbs could be built with sensors on fingertips or other important areas. When a stimulus, such as pressure or temperature, activated these sensors, an electrical signal would be sent to an actuator, which would produce a similar stimulus on the "rewired" area of chest skin. The user would then feel that stimulus as if it were occurring on an appropriate part of the artificial limb.
Recently, robotic limbs have improved in their ability to take signals from the human brain and translate those signals into motion in the artificial limb. DARPA, the Pentagon’s research division, is working to make even more advancements in this area. Their desire is to create an artificial limb that ties directly into the nervous system.
The main disadvantage of this method is that amputees with the direct bone attachment cannot have large impacts on the limb, such as those experienced during jogging, because of the potential for the bone to break.
There is currently an open Prosthetics design forum known as the "Open Prosthetics Project". The group employs collaborators and volunteers to advance Prosthetics technology while attempting to lower the costs of these necessary devices. Visit their site at http://OpenProsthetics.org.
A plan for a low-cost artificial leg, designed by Sébastien Dubois, featured at the 2007 Indernational Design Exhibition award show in Copenhagen, Denmark. It plans to be able to create an energy-return prosthetic leg for US 8 dollars, composed primarily of fiberglass.