- Terminal Devices:
- Functional Hooks vs. Cosmetic Hands;
- Hooks: Voluntary opening vs closing:
- voluntary opening:
- more popular & are recognized by their numbers of rubber bands (# is proportional to pinch strength, w/ 3 bands equal to about
3 lbs of pinch strength, which is adequate for adl's;
- voluntary closing:
- held open by spring & allow graded prehension & powerful grip;
- pts may tire w/ prologed holding of objects w/ vc components;
- they are bulkier, less durable, and more expensive;
- myoelectric prosthesis:
- operates more efficiently closer to body & w/ over head activity;
- BEA Prosthesis:
- is controlled w/ one cable system (single control);
- terminal device control:
- ipsilateral shoulder motion applies tension on prehensile terminal to allow it to function;
- controled w/ biscapular abduction & shoulder flexion on amputated side;
- returning shoulder to starting position relaxes tension on cable allowing rubber bands to close fingers of terminal device;
- location of ring or cross point or harness:
- in order to provide greatest mechanical advantage, comfort, and minimum amount of work on part of amputee, ring or cross point
should be situated below spinous process of 7th cervical vertebra & slightly toward non amputated side;
- this location causes cable control strap to cross distal third of scapula on theprosthetic side, taking full advantage of scapular
mobility for cable excursion;
- elbow hinges:
- used in BEA, and can be flexible (permit pronation/supination in long BEAs) or rigid (for higher level amputees);
- Above Elbow Prosthesis:
- usually operated by two separate control cables;
- one cable flexes elbow & opens terminal device whereas second cable locks and unlocks the elbow joint;
- because of cable housing, amputee can maintain terminal device in open position throughout the range of elbow flexion;
- fingers can be opened or closed w/ elbow fully extended or flexed;
- cable housing serves to maintain fixed length of two ends of control cable regardless of whether or not elbow is flexed;
- elbow flexion is made possible by split housing of the control cable;
- locking & unlocking of elbow joint:
- is controled by cable running from anterior suspension strap to elbow that operates on alternator principle;
- elbow locking is controlled by slight extension, abduction, and depression of the shoulder;
- terminal device:
- operates after elbow is locked in the desired position;
- humeral flexion or biscapular abduction (protraction) opens T.D.
- optimal mechanical efficiency of figure of 8 harnesses occurs w/ placement of the straps to cross just below spinous process of C7
and slightly toward the non amputated side
