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A terminal device simply describes the terminal or component at the end of an upper extremity prosthesis, and they come in all shapes and sizes. Some are more lifelike than others, while others are less cosmetic but provide higher function. From advanced computer controlled components to simple open and closing mechanisms, terminal devices aim to restore function to the upper extremity. There are two major classes of terminal devices, hands and hooks.
Sized to match your sound side hand, both body and externally powered hands restore both appearance and function. Many prosthetic hands are closed at rest and open with body movement (body power) or muscle contraction (external power), depending on the design of your prosthesis. Prosthetic “skins” are typically used over the hand to match the skin tone of the user.
A cable extending from the base of a body powered hand is connected to a harness worn by the user. When specific body movements are performed, tension is placed on the cable which opens and closes the thumb in relation to the index finger. This “pinch” grip is able to pick up light objects. The remaining fingers can be prepositioned, but do not actively move.
There are many types of externally powered hands, from hands with a moving thumb (like body powered hands) to more complex microprocessor controlled components with 5 individually moving fingers. Externally powered hands receive input from electrodes imbedded in the socket that pick up the muscle signals from the residual limb to open and close the hand. A chargeable battery within the prosthesis provides the “external power” to allow the hand to function.
Non-microprocessor hands were some of the first myoelectric components to emerge on the market. The movement of the thumb and index finger are similar to that of a body powered hand, but the open and close commands are generated from signals received from the electrodes located inside the socket. Non-microprocessor hands allow users to take advantage of myoelectric technology without the microprocessor price tag.
Microprocessor controlled hands are the most advanced upper extremity prosthetic components. An onboard microprocessor receives input from the electrodes and generates specific commands and hand grasping patterns, based on programming by the prosthetist. Most body powered and non-microprocessor hands have one grasp pattern, opening and closing of the thumb and index finger, whereas microprocessor hands can have up to 21 grasp and gesture patterns. Unfortunately, microprocessor hands can be quite costly and begin around $75,000 for the hand alone.
P&O Care prosthetists are certified to fit the following Microprocessor Hands:
Otto Bock Michelangelo Hand
Touch Bionics iLimb Ultra, Pulse, Quantum Hands
Different grasp patterns
Heavier than Body Powered Hands
Not as durable
Cannot be used in wet environments
While they may look intimidating, hooks can be very useful tools for an upper extremity amputee. Extremely lightweight and cost effective, hooks are extremely durable and useful. There are many different styles of hooks, made of different materials, shapes and sizes depending on the users needs. Hooks can be both body powered or externally powered.
Can be used in dusty or wet environments
Easy to use
Often, some patients like to wear a hook for their day-to-day activities, but prefer to use a hand for more formal occasions or social events. A quick change wrist is a special receiver on the end of an upper extremity socket that allows the user to quickly change from one terminal device to another. A patient can change from a hook to hand to a special use terminal device in a matter of seconds.
Bilateral upper extremity fittings can be quite complex, and require an extensive, experienced and accessible team. P&O Care prosthetists are equipped to handle the most complex cases and allow patients to return to independent living.