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, and 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 control systems available in these prostheses: myoelectric and switch control. A myoelectrically-controlled prosthesis uses signals from the muscle to activate the prosthesis, as 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 the speed or activation varies with the intensity of the muscle contraction. Myoelectric 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 advances in materials and design, some passive hands are virtually lifelike.
However, most of these cosmetic prostheses are usually less functional and more expensive than active terminal devices.
Shoulder Disarticulation / Forequarter Amputation is the removal of the entire arm including the shoulder blade and collar bone. A high level of function can be difficult to restore. Many patients learn how to accomplish activities of daily living using the intact limb and for their amputated side, prefer a passive/cosmetic prosthesis to give their body symmetry and improve balance.
However, there are advances in upper limb myoelectrics, which can be an alternative to some. Myoelectric arms work using electronic sensors to detect muscle, nerve and EMG activity generated by the patient. These signals are relayed to various electric motors, which enable the patient to grip and move the prosthesis in an effective manner.