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Today's VeTerinary PracTice | november/december 2015 | tvpjournal.com a PracTiTioner's Guide To FracTure ManaGeMenT Peer reviewed 32 • Never place IM pins into the radius due to high likelihood of joint penetration into the carpus or articular surface of the radial head. • Avoid stack pinning—placing multiple small pins to replace one large pin—and threaded pins—those with a threaded endface; stack pinning does not provide any additional rotational support and threaded pins tend to fail at the thread pin interface. 1 INTERLOCKING NAIL An ILN is similar to an IM pin, but is secured to the bone by bolts or screws that are placed proximal and distal to the fracture, passing through pre-existing holes in the nail. ILNs are similar to IM pins with regard to placement; however, they are superior for preventing rotational and shearing forces (due to the bolts/screws) and countering bending and compressive forces. Indications ILNs are useful for fractures in which the bone cannot be reconstructed, such as highly comminuted fractures. This fxation method typically results in very rigid repairs that can counteract all forces and are entirely load bearing until bone healing has progressed to callus formation. ILNs are also helpful when limited bone length is available proximally or distally, as their corresponding bolts do not require much available bone length for placement. Benefts Versus Risks Benefts of ILNs include placement with a minimally invasive technique, allowing the fracture hematoma to remain untouched. This principle of minimal disruption at the fracture site allows for healing to progress undisturbed, optimizing the biological environment for healing. However, some of the same limitations seen with IM pin placement must be considered when placing ILNs: the articular surface must be carefully avoided during placement; thus, placement in the radius is not advisable and, while placement in the tibia is possible, it is slightly more challenging. Technique ILNs are locked in place with bolts or screws that penetrate the cortex and thread through pre-existing holes at the proximal and distal aspects of the nail. Depending on nail type and number of holes distally and proximally, the number of screws or bolts placed varies. During surgical placement, a jig must be used to ensure that the bolts appropriately line up with the holes in the nail. A newer, angle-stable ILN (I-Loc, biometrix. com) was developed to overcome the concerns of instability in bending and torsion that is seen with traditional ILNs. It has a novel hourglass shape that provides increased strength due to a larger diameter Orthopedic Hardware: IM Pin & Cerclage Wire IM pins and Kirschner wires (K-wires) are made from 316L stainless steel. The difference between pins and k-wires is mainly diameter: IM pins—also referred to as Steinmann pins—are between 1.5 mm (1/16 inch) and 6.5 mm (1/4 inch) in diameter, while K-wires are 0.9 to 1.5 mm (0.035, 0.045, 0.062 inches) in diameter. 1 The most common pointed ends for IM pins are 3-sided trocar tips or 2-sided chisel tips: trocar tips are better suited for penetration of cortical bone, while chisel tips can be braced against the endosteal surface of the bone's cortex or lodged in cancellous bone. 2 Some IM pins may be partially threaded; however, when placed in the medullary cavity, partially threaded IM pins do not have any better holding power than standard smooth threaded pins (see Cautions). Cerclage wire comes in various sizes, ranging from 0.635 mm (22 gauge) to 1.02 mm (18 gauge). The correct size must be used based on patient size: 1 ` Cats and very small dogs: 20 to 22 gauge ` Small, medium, and large breed dogs: 18 to 22 gauge ` Giant breed dogs: 16 gauge. FIGURE 2. Lateral (A) and craniocaudal (B) radiographs of mid-diaphyseal comminuted tibial fracture stabilized with the I-Loc ILN; on the craniocaudal (B) radiograph, note the hourglass design of the nail, with 2 bolts placed proximal and 2 bolts placed distal to the fracture. Courtesy Dr. Cory Fisher A B