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Terminal device

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A terminal device is the prosthetic component that is designed to substitute hand function. It can be classified as active or passive. Passive terminal devices are highly use for a cosmetic appearance but sometimes can be used to stabilize an object during bimanual activities. On the other hand, active terminal devices are commonly used for function which hand and hook terminal devices are the two basic types. Although hand terminal devices restore the natural look, they are heavier and more expensive. Moreover, many of material used are vulnerable to both mechanical and chemical damage. Active terminal devices can be powered by a mechanical cable-driven (body powered) or an externally powered (switch controlled or myoelectric) systems.

Voluntary opening vs Voluntary closing

In a voluntary opening system, elastic bands or a spring are used to hold the active terminal device (hand/hook) in a closed position. To open the hand, the person must generate enough tension to through the cable system in order to overcome the force of elastic bands or a spring.

In a voluntary closing system, the mechanism is opposite to a voluntary opening system. For this system, the elastic cords or a spring are used to hold the terminal device in an open position unless the wearer activates the cable system to close the device. To continue holding or grasping an object, the wearer must maintain tension level on the cable.

Body powered vs Myoelectric

Body powered control is the oldest and the most popular method, in which the user operates the prosthetic device through the user’s motion. There are several factors that contribute to the popularity of body powered control such as inexpensive cost, low maintenance, lighter weight, etc. However, the most important factor is the proprioceptive feedback through the harness.

Body powered control
Body powered control

Author: Weerawat Limroongreungrat
Affiliation: Division of Physical Therapy, Georgia State University
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