Artificial limb: Encyclopedia - Artificial limb

Artificial limb

Artificial limbs are a type of prosthesis and are classified by the type of amputation they would replace, for example:

• Transtibial: Below the knee
• Transfemoral: Above the knee
• Transradial: below the elbow
• Transhumeral: above the elbow

For congenital (from birth) defects the terms are used to refer to the body part that would be amputated. For example if one of the limbs is very short and the foot is at the level of the 'normal' shin then the prosthesis would be described as a transtibial prosthesis even though the Tibia is fully intact.

Any artificial limb is attached to a persons body, to replace a missing part of the body. They used to be made from wood and certain types of metal, but have now been replaced with more lightweight material such as fiberglass.

Artificial limbs in the past had no mobility. Then they were replaced with models that had joints and so could be bent (if unnaturally and not automatically) and fixed in different positions for different types of activities (for example, sitting and walking). These, in turn, were replaced with robotic models capable of moving by themselves when controlled by an internal computer or directly by the user. In the past they could be controlled either by other muscles (for example, on the back), but today direct neural control is preferable.

Artificial limb - Conventional control of powered prosthetic limbs

The myoelectric signal is an electrical signal which is the result of a muscle contraction. This signal travels throughout the body and can be detected at the skin's surface. Prosthetic limbs are usually controlled detecting these myoelectric signals over specific control sites located around the residual limb. For example, someone with a transhumeral amputation could use the signals from the muscles of the biceps and triceps to control a prosthetic limb. The user would contract what remains of their bicep or tricep and the intensity or rate of change of these signals determines which function and how fast the prosthesis should move. Recently, patterns in the myoelectric signal have been investigated and have potential to provide superior control.

Artificial limb - Direct neural control of prosthetic limbs

Limbs and appendages are moved by muscles, which are stimulated by very small amounts of electricity (microvolts) from the nervous system. Even if the limb or appendage is absent, the nerves and impulses controlling the missing limb are (usually) still there, and the brain can send microvolts of electricity to guide a "phantom" limb. If these currents are amplified and sent to a motor in the artificial limb, that limb can be moved via the same method used to control natural limbs. The current challenge for medical science is to perfect the system, as refining the technology is an ongoing process.

Artificial limb - Costs

Many people in developing countries, particularly victims of landmines, can't afford even the most basic artificial limbs.

Artificial limb - Limbs for non-humans

• In 2004 a dolphin in the Okinawa Churaumi Aquarium, who lost most of its fin because of necrosis, got an artificial fin that allows it to swim as fast as a healthy dolphin can and jump from the water.

• In 2005 an elephant in Lampang, Thailand that had lost its left front foot was fitted with a temporary prosthetic foot in preparation for being fitted with a permanent foot.

Adapted from the Wikipedia article "Artificial limb", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki