Page 340 - WSAVA2018
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 25-28 September, 2018 | Singapore
IM Pin Summary
Intramedullary pins are uniquely capable of resisting bending forces in all planes, but this is the extent of their abilities.Therefore, IM pinning typically requires some form of appropriate supplemental secondary or primary fixation.
Cerclage Wire Fixation
To understand the ability of cerclage wire to resist these disruptive forces, the principles of proper cerclage wire application must first be discussed.
Only for Perfectly Reduced Long Oblique or Spiral Fracture Configurations
Full-cerclage wire fixation is an encircling wire that
is capable of generating significant interfragmentary compression between the 2 bone segments, but only when properly applied to LONG oblique or spiral fracture configurations. The length of the fracture line must be at leasttwice the bone diameter; fracture lines that are 3 times the bone diameter permit greater interfragmentary compression (ie, improved fracture stability). Sufficient interfragmentary compression is only achieved when
the long oblique or spiral fracture configuration can
be perfectlyreduced (in this instance, “close” doesn’t count!). After closely studying your high quality, orthogonal view radiographs, one simple rule kept in mind can save you a lot of problems: if you see multiple cortical fragments (especially small ones), “put down the wire and nobody gets hurt!”.
One Cerclage Wire is Never Enough for Fracture Stabilization
A single cerclage wire is neversufficient to stabilize 2 main fracture segments because it concentrates all of the disruptive forces into this single site. When properly used to stabilize a long oblique or spiral fracture configuration, each cerclage wire adds to the interfragmentary compression that is achieved. When proper wire
spacing is used (discussed below), insufficient room for
a 2ndcerclage wire indicates that the fracture line is not sufficiently oblique for effective use of cerclage wiring.
Proper Cerclage Wire Spacing is a Must!
Proper wire spacing is required to permit vascular inflow and outflow from the cortical bone while achieving
the needed interfragmentary compression. Adjacent cerclage wires are to be spaced 1 bone diameter apart from one another. Cerclage wires placed adjacent to the tips of long oblique/spiral fracture lines should be at least 1⁄2 bone diameter from the tip of the segment. Note that
if a fracture line is less than 2 bone diameters in length, it would only be possible to place a single cerclage wire when the rules of proper wire spacing are applied. A fracture line that is 2 bone diameters in length will permit proper application of 2 cerclage wires and a fracture line that is 3 bone diameters in length will permit application of 3 cerclage wires.
Use the Correct Size of Wire
In small animal orthopedic surgery, 18gauge wire is used for medium and large breed dogs, 20gauge wire is used for medium and small breeds of dogs, and 22gauge is used for most cats and toy breed dogs. Braided wire is not used because it is not possible to generate sufficient wire tension with conventional tensioning and knotting techniques.
Cerclage Wire Knots
The twist knot is the most frequently used method to tighten and secure cerclage wires. In this technique,
it is important that tension be applied as the wire is twisted in order to twist the wire ends uniformly around one another like a barber pole. On occasion, one end
of the wire while twist upon the other like a snake on stick; this twist knot is not secure and the wire should
be replaced. When an adjacent cerclage wire is placed, the additional interfragmentary compression that is produced often causes subtle, but relevant, loosening
of the first wire. For this reason, when using twist knots, do not cut the twisted wire until all cerclage wires have been applied because additional tightening cannot be achieved once the wire is cut. Twist knots are usually
cut between the 3rdand 4thtwist. Bending the twist knot after the wire has been cut loosens the wire, so the twisted tip is usually left protruding into the soft tissues where a fibrous capsule will form around it. If there are critical neurovascular structures adjacent to the twist,
the knot can be twisted as the wire is bent toward the cortical surface in attempt to minimize the loss of tension associated with bending. Single- and double-loop knots can also be used and have their own distinct advantages and disadvantages. While there are mechanical advantages (especially for double-loop knots), one of the key disadvantages is the requirement for purpose- specific instrumentation. Practically speaking, any these forms of cerclage wire fixation can be used effectively in most instances provided the principles of proper use are strictly adhered to.
Preventing Cerclage Wire Loosening
Loose cerclage wires do not impart interfragmentary compression and, worse yet, they interfere with bone healing because they disrupt blood flow in and out of the bone. In short, “loose wires kill”. In order to minimize the risk of loosening, full cerclage wires should oriented perpendicular to the long axis of the bone. As previously mentioned, application of an adjacent cerclage wire can loosen a wire that was previously tight; therefore, it is vital that all wires be checked for tightness immediately prior to surgical closure. For my pre-closure “wire- looseness” check, I like to use a periosteal elevator to try to shift each wire up or down the bone. Any loose wires are re-tightened (if possible) or replaced; a little extra work here can save hours of work and agonizing in the weeks to come. In conical segments of bone, cerclage

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