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IDS_Ireland_prosthetics_orthotics IDS Ireland offer this free resource for Healthcare Professionals who are encountering prostheses and or orthoses for the first time, or are only occasionally in contact with them. IDS_Ireland_prosthetics_orthotics_IDS Ireland offer this free resource for Healthcare Professionals who are encountering prostheses and or orthoses for the first time, or are only occasionally in contact with them. IDS_Ireland_prosthetics_orthotics_IDS Ireland offer this free resource for Healthcare Professionals who are encountering prostheses and or orthoses for the first time, or are only occasionally in contact with them. IDS_Ireland_prosthetics_orthotics_IDS Ireland offer this free resource for Healthcare Professionals who are encountering prostheses and or orthoses for the first time, or are only occasionally in contact with them.
IDS_Ireland_prosthetics_orthotics_IDS Ireland offer this free resource for Healthcare Professionals who are encountering prostheses and or orthoses for the first time, or are only occasionally in contact with them.

IDS ::: Prosthetics ::: Upper Limb Power

Power source mechanisms

An upper limb prosthesis can be mainly functional, mainly cosmetic or a combination of both. If functional, the power to operate it will probably be from one or more of the following sources:
  • Body powered: generally by means of biscapular abduction creating tension via a harness into a cable.
  • Myoelectric

Body Powered

A transtibial exoskeletal prosthesis with body powered voluntary closing spilt hook.
A simple shoulder harness and operating cord mechanism.
An exoskeletal body powered transhumeral prosthesis.
Split hooks are normally body powered here are examples of adults.
Examples of children's split hooks with soft covers for safety.

Overview of possible body powered functions

  • Grasp – by opening the prosthetic hand or terminal device. Closing is normally powered by a spring, but this is sometimes the reverse.
  • Elbow flexion – extension is normally achieved by gravity.
  • Locking/unlocking of the elbow.
  • Note! All of the above are controlled and powered by biscapular abduction – Not easy!

Myoelectric
Electrodes incorporated into the prosthetic sockets pick up micro signals on the skins surface. These signals are amplified by battery power. The amplified current drives a motor via a clutch.

Possible myoelectric functions.

  • Grasp – by opening and closing the prosthetic hand or terminal device.
  • In some cases the speed or power can be proportional to the strength of signal.
  • Rotation of the hand or terminal device – this mimics pronation/suspiration.
  • Elbow flexion./extension

Myoelectric considerations

  • The components are expensive.
  • They require space to be incorporated.
  • They can be heavy, especially when more than one function is included e.g. grasp and rotation.
  • Not all patients can generate the required signals or control them adequately.
  • These prostheses are not suitable for frequent heavy use.
  • Two electrode sites are not always essential.
 Inserting the rechargeable battery for the Myoelectric prosthesis.
A Myoelectric transradial prosthesis cut away to show construction.

Sensor hand - the internal mechanism of the sensor myoletic hand.

Transparent transcarpal hand.

A Myoelectric hand and greiffer terminal device, showing internal components which power the hand or Greiffer.

A young man using a Greiffer hand.

A greiffer hand is an alternative to the normal myoletic hand. Its design permits much more precise grip for technical tasks and also permits better visual feedback.

Examples of hands and internal mechanisms
Examples of hands and internal mechanisms


Myoelectric considerations

  • The components are expensive.
  • They require space to be incorporated.
  • They can be heavy, especially when more than one function is included e.g. grasp and rotation.
  • Not all patients can generate the required signals or control them adequately.
  • These prostheses are not suitable for frequent heavy use.
  • Two electrode sites are not always essential.
 A relatively high degree of dexterity can be achieved with both body powered and myolectric hands.
A body powered hand and cover.
A close up of a Greiffer hand.
The internal view of a child's Myoelectric hand.
A Myoelectric electrode
A Myoelectric motor
   
IDS_Ireland_prosthetics_orthotics_IDS Ireland offer this free resource for Healthcare Professionals who are encountering prostheses and or orthoses for the first time, or are only occasionally in contact with them.
IDS_Ireland_prosthetics_orthotics_IDS Ireland offer this free resource for Healthcare Professionals who are encountering prostheses and or orthoses for the first time, or are only occasionally in contact with them. IDS_Ireland_prosthetics_orthotics_IDS Ireland offer this free resource for Healthcare Professionals who are encountering prostheses and or orthoses for the first time, or are only occasionally in contact with them. IDS_Ireland_prosthetics_orthotics_IDS Ireland offer this free resource for Healthcare Professionals who are encountering prostheses and or orthoses for the first time, or are only occasionally in contact with them. IDS_Ireland_prosthetics_orthotics_IDS Ireland offer this free resource for Healthcare Professionals who are encountering prostheses and or orthoses for the first time, or are only occasionally in contact with them.