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Transfixation Wire Properties

- See:
      - Safe Zone of Pin Insertion
        Wires Insertion Techniques

- Wire Characteristics:
    - in general 1.5 to 1.8 mm wires need no incision or drill sheath, but larger, 2.0 wires may be inserted w/ sheath through incision;
           - larger diameter wires will increase stiffness of the frame;
           - generally, the 1.8 mm wire is used for the humerus, tibia, and femur;
           - in smaller patients 1.5 mm wires should be used;
    - whether a ring or unilateral fixator is used, there is some evidence that a better regenerate is formed with the use of titanium half pins rather than transfixation wires;
           - ref: Limb lengthening by callus distraction (callotasis).
      - wire tips:
             - trocar tip is used for metaphyseal bone;
             - bayonet tip is used for diaphyeal bone;
                    - it produces a hole of slightly larger diameter than that of the wire;
             - these wires have a special cutting tip so that predrilling is not required;
      - olive wires:
             - used to assist in indirect reduction;
             - wire is inserted w/ goal of applying tension to the ball inorder to pull the fracture into alignment;
             - olive wires require a small incision of skin only;
             - cautions: olive wires may tend to cut thru cancellous bone, resulting in loss of reduction;
             - note: when olive wires are inserted they should be marked in order that the correct end will be pulled out bone at the time of fixator removal;

      - titanium pins:
             - see: properties of titanium;
             - may have a lower incidence of infection than stainless steel;
             - more flexible than stainless steel, however, use of 6 mm pin brings pin stiffness up to par w/ stainless steel;

- Ring Characteristics

- Stability of Construct / Position of Pins:
      - see safe zone of pin insertion for tibial frx;
            - it is safest to insert pins from the more vulnerable side to the less vulnerable side;
      - wire diameter and wire tension are important factors in frame stability;
      - large fragments require 2 levels of fixation w/ 2 wires (or one wire and one half pin) at each level of fixation;
      - short fragments may be fixed w/ one ring w/ a drop wire (in which case the insertion pin is offset from the ring by 1-2 cm);
      - stability is increased by having pins transfix bone at right angles at each level within anatomic constrainst;
            - if pins are to be crossed at the same level, it is prudent to insert one pin above the ring and another below the ring;

- Pin Attachment to Frame:
    - never bend a pin to meet a frame, but instead, either remove and reinsert the pin, or use spacers to attach the pin to the fixator;
    - wires are attached to ring using either cannulated or slotted fixation bolts, the choice depending on which bolt minimizes wire bending;
    - w/ one wrench holding the fixation bolt stationary, the remaining wrench tightens the fixation nut;

- Wire Tensioning:
    - tensioning is performed thru slotted wire fixation bolt;
    - tensionig is carried out by fixing one end of the wire and tensioning the other wire;
    - frame stiffness will be increased by increasing wire tension, which has the effect of decreasing motion at the fracture site;
    - note when drop wires are used, the tensioner will not have the ring to act as a counter post;
          - in this situation, introduce a hexagonal post between the drop wire's fixation bolts and then tensioner (and then apply the tensioner in the usual way);
    - wires are tensioned between 100-130 kg of force;
          - exceptions:
                - drop wire: 50 to 80 kg;
                - single wire on a ring 100 kg;
                - olive wire: 100 kg;

- Post Op:
    - it is essential to check periarticular wires for signs of inflammation or superficial infection, in order to avoid possible septic arthritis;
    - it is essential that the wire tension be checked, since loss of tension will result in loss of frame stability

The use of wires and pins. Green SA. Techn Orthop. 1990;5:19-25.

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