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Multisegmented Hook Instrumentation

- See: Cotrel-Dubousset

- Discussion:
     - multisegmental hook systems, like CD and TSRH, provide multiple points of fixation to the spine and allow both compression and
           distraction on the same rod;
    - added strength is obtained w/ use of several transverse traction devices, which convert the system to rigid rectangle;
    - addvantages:
          - postop bracing is minimized w/o jeopardizing reduction & fusion;
          - allows use of shorter instrumentation & immobilizing of fewer segments;
          - hooks can be used in both distraction & compression modes, allowing complex curve correction and providing stability w/ 
                segmental fixation;
         - improved correction of thoracic hypokyphosis (upto 10 deg);
         - preservation of lumbar lordosis;
         - derotation of the spine;
         - postoperative immobilization is not required;
    - disadvantages:
         - require more time to insert than do the other posterior systems;
         - moderate amount of manipulation is required to connect multiple hooks to rods while reducing unstable spine injury;
- Technical Points:
    - length of lever arms be equal above & below frx;
    - double lamina claws be applied at both cephalic &caudal ends of fixation;
    - hook placement;
          - hooks are placed into areas where there is no canal compromise;
          - in cases of frx w/ severe retropulsion, do not place sublaminar hooks at T12 for an L1 Burst fracture, since canal is narrowest 
                at this site;
                 - instead proximal claw is placed one level cephalad to routine levels