photo source: http://www.healthcare.ottobock.com/technical_orthopedics/armprothesen/sites/cable.htm
Description
In a body-powered prosthesis, motion is transmitted to the prosthesis
via a cable control system. The cable either runs from the prosthetic
arm across the back to a loop around the healthy shoulder or it is harnessed
to the healthy wrist. The motion of the “hand” device may
be powered by either abduction of the shoulder or by flexion of the wrist.
In this way transmission of motions by the wearer’s own actions
gives the wearer a sense of motion and connectedness to the prosthetic.
The two main types of body-powered hands are VO (voluntary open), and
VC (voluntary close). With VO, the hand is opened with the cable and closes
automatically and with VC the hand closes when tension is applied to the
cable. The prostheses may terminate with either a hook or with a cosmetic
artificial hand.
Advantages
The body-powered system has several advantages. Low cost and high reliability
makes it accessible and dependable. Lightweight and simplicity combined
with kinesthetic feedback make it less cumbersome and more personal than
other systems. Therefore, although there are big developments in externally-powered
prostheses, they are not likely to completely obliterate the use of the
body-powered system.
Disadvantages
Although a cosmetic glove or covering may be applied to the prosthesis
in order to make it look aesthetically “normal,” the wearer
still needs to make abnormal movements of the shoulder or wrist in order
to operate the prosthetic hand. These movements may bring unwanted attention
to the wearer and may also compromise the action and range of action of
the prosthesis. Additionally, persons with severe scar tissue, or the
inability to generate sufficient force may not be able to operate a body-powered
prosthesis. Body-powered systems are generally less cosmetically pleasing
than passive or myoelectric models.
References
1) Bodeau, Valerie S. “Upper Limb Prosthetics.” 2002. eMedicine:
Instant Access to the Minds of Medicine. 23 Apr. 2003. <http://emedicine.com/pmr/topic174.htm>.
2) “Cable Controlled Prostheses.” Otto Bock – Cable Controlled Prostheses. 23 Apr. 2003. <http://www.healthcare.ottobock.com/technical_orthopedics/armprothesen/sites/ cable.htm>.
3) Carlson, Lawrence E. and D. Eng. “Improved Control of Body-Powered Prehension.” 1997. University of Colorado at Boulder. 26 Apr. 2003 <http://spot.colorado.edu/~carlsole/ISPO97.html>.
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