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used with minimally-invasive technique. Many fractures of the radius and tibia can be reduced closed and stabilized with an external fixator. The main disadvantage is the potential for complications with premature pin loosening and the added care needed in the postoperative period. The use of external fixators for fracture repair is not optimal if the patient or owner is likely to have poor compliance in the postoperative period. External fixators frames can be applied in one of 3 configurations- linear, circular or as a hybrid of linear and circular.
Plate-rod construct
The plate rod system has been found to be an ideal implant system for biological fracture management. Management of a non-reducible diaphyseal fracture with a combination of
an IM Steinmann pin and bone plate can be applied without anatomical reconstruction and thus, avoids the development of small fracture gaps with high interfragmentary strain. The addition of the IM pin to the plate also significantly increases the construct stiffness and estimated number of cycles to fatigue failure when compared to a plate only construct. An IM pin serves to replace any trans-cortical defect in the bone column and acts in concert with the eccentrically positioned plate to resist bending.2 Mathematical analysis of the plate- rod construct in the canine femur demonstrated that the pin and plate act most like a dual-beam structure, assuming slight motion of the pin in the canal.2 Addition of an IM pin to a bone plate has been shown by Hulse et al. to decrease strain on the plate two-fold and subsequently increase the fatigue life of the plate-rod construct ten-fold compared to that of
the plate alone.1 In the canine femur, plate strain is reduced by approximately 19%, 44%, and 61% with the addition of an IM pin occupying 30%, 40% and 50% of the marrow cavity, respectively.3 Stiffness of plate-rod repairs may be as much as 40% and 78% greater when the pin occupies 40% and 50% of the marrow cavity, respectively.2Ideal diameter of the IM pin should be between 30 and 40% of the medullary canal diameter measured at the istmus. Increasing diameter up to 50 dramatically challenge the ability to insert screws trough the plate holes.
Locking Plates
Locking plates have become very popular for minimally- invasive fracture repair. Many locking plate systems are available including the Synthes, FIXIN, SOP and ALPS. Locking plates have the ability to lock the screw into
the hole of the plate. The mechanism for locking varies amongst manufactures. The Italian design FIXIN locking plate system has a conical locking mechanism while the Synthes system has a threaded locking mechanism. The FIXIN plate hole is tapered to match the conical nature of the head of the screw. This type of fitting is similar to the Morse taper of the head and neck fitting of the Total Hip Replacement implant. The stability of this design
is extremely secure. The Synthes locking plate has threaded holes in the hole of the plate. Corresponding threads in the head of the screw engage the threads of
the hole, locking the screw to the plate. The ability to lock the screw to the plate increases pull-out strength
of the screw and construct stability. Traditional plates
do not have threaded holes. Screws placed in ordinary plates apply pressure to the plate, pressing it onto the bone surface. The friction between the plate and the bone provides the stability to the bone-implant construct. In contrast, the locking plate achieves stability through the concept of a fixed-angle construct. The locking plate is not pressed firmly against the bone as the screws
are tightened. The locking screws and plate function more like an external fixator. Locking plates are essential “internal fixators.” The plate functions as a connecting bar and the screw functions as a threaded fixator pin. The tapered or threaded head of the locking screw engages the hole of the plate, similar to the clamp of an external fixator. The Synthes locking plate also has combi-holes which allow use of traditional or locking screws when desired. Traditional screws should be place prior to locking screw when using locking plates.
Locking plates are ideal for minimally-invasive fracture repair for several reasons. Blood supply to the bone
is preserved because the plate is not pressed tightly against the bone. The plate does not require perfect anatomic contouring because the displacement of the plate will not occur as the screw is tightened into the hole of the plate. Accurate contouring is difficult with a minimally-invasive approach due to the minimal exposure to the shaft of the bone. Lastly, locking screws give fixed angle support to the non-reduced fracture, increasing stability and less chance of collapse and instability at the fracture gap.
Interlocking nail
The Deuland interlocking nail system presently available in the U.S. (Innovative Animal Products, Inc., Rochester, MN) is a modified Steinmann pin modified by drilling one or two holes proximally and distally in the pin,
which allows the placement of transverse bolts or screws through the bone and nail. The nail, bolts and screws can be applied in closed or open fashion due
to the incorporation of a specific guide system that attaches to the nail. The equipment needed to place
the nail includes a hand chuck, extension device, aiming device, drill sleeve, drill guide, tap guide, drill bit, tap, depth gauge, and screwdriver. Cost of the system is reasonable and each nail is approximately half the cost of a comparative bone plate. The nails are available in diameters of 4.0, 4.7, 6, 8 and 10 mm and varying lengths and hole configurations. The 4.0 and 4.7 mm nails use 2.0 mm screws or bolts. The 6 mm nail is available in two models and will accommodate either 2.7 or 3.5 mm screws or bolts. The 8 mm nail is also available in two models and will accommodate either 3.5 or 4.5 mm screws or bolts. The 10 mm nail uses 4.5mm screws
or bolts. The solid cross locking bolts have a larger
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