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Upper Extremity Prosthetics



- 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