Conventional or body-powered arm prosthesis is so-described because it is operated with body power alone, and is not externally powered. Conventional or body-powered prostheses are the most durable prostheses. They are also moderate in cost and weight. However, a body-powered prosthesis is less cosmetically pleasing than myoelectrical-controlled type and also requires more gross limb movement.
A myoelectric prosthesis uses muscle contraction as a signal to activate and control the prosthesis. Batteries and motors are used to operate these prostheses. There are two different types of controls systems available in these prostheses: myoelectric and switch control. A myoelectrically-controlled prosthesis uses signals from the muscle to activate the prosthesis. It detects electrical activity from limb muscles, with surface electrodes.
Switch-controlled prostheses use small switches, rather than muscle signals, to operate the prosthesis. These switches are typically enclosed inside the socket or incorporated into the suspension harness of the prosthesis. A switch can be activated by the movement of the remnant digit or bony prominence against the switch, or by pulling on a suspension harness.
Many myoelectric control systems allow the use of proportional control so that the speed or activation varies with the intensity of the muscle contraction. Myoelechic prostheses include:
Cosmetic shoulder and forequarter restoration prostheses provide body balance and improve a patient’s appearance.
The main advantage of most cosmetic restoration prostheses is their cosmetic appearance. With the advances in materials and design, some passive hands are virtually indistinguishable from native hands.
However, most of these cosmetic prostheses are usually less functional and more expensive than active terminal devices.
In circumstances where amputation is required at the shoulder or forequarter level, the function is difficult to restore. In the past, due to a combination of factors: the weight of prosthetic components and decreased function due to multiple joints, a purely cosmetic prosthesis is used to improve body appearance and to improve body balance.
At present, however, a myoelectric arm offers amputees with forequarter and shoulder disarticulation a more realistic solution. The myoelectric arm works under the influence of electric signals extracted from the skin surface. These signals are used to run various motors which enable the patient to grip and move limbs in an efficient manner.