Article: Artificial limb

A United States soldier demonstrates Foosball with two prosthetic limbs

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

• Transtibial prostheses: Below the knee
• Transfemoral prostheses: Above the knee
• Transradial prostheses: below the elbow
• Transhumeral prostheses: 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 person's 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 by other muscles (for example, on the back), but today direct neural control is preferable.

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.

In September 2005, Popular Science reported on a prototype neurally controlled limb developed by The Rehabilitation Institute of Chicago's amputee program. This prosthesis required a unique surgery that rerouted multiple nerves, which were once connected to the arm of the user, to his chest, where the nerves interfaced with various electrodes. This design is the first neurally controlled prosthesis to move simultaneously at the shoulder elbow and wrist. It contains a 64-bit computer to co-ordinate its movements and allows the user to actually sense pressure when grasping an object.

Costs

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

The Department of Mechanical Engineering at the University of Waterloo (Waterloo, Canada) is currently developing a semi-active prosthetic leg geared specifically for landmine victims in Afghanistan. This prosthetic is geared specifically for trans-femoral amputees.

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.