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Universal dynamizable linear fixator 

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Technique for use 

Foreword 
The dynamizable external fixator Dynamic 2.0 is a veterinary surgical device, whose use is restricted to veterinary surgeons who are thoroughly familiar with the procedures and directions for use. Ad Maiora is not liable for any use other than the purpose for which it was designed, or not following the correct method of use. 
The following guidelines do not represent in any way a suggestion for using the fixator on clinical patients. The decision on its application depends exclu-sively on the judgment of the surgeon. 


Technical note 
The current version of the fixator (Dynamic 2.0) is different from the one rep-resented in the images of the instructions. The technique of use, however, has remained the same, so you can still refer to these instruct
ions for all ver-sions of the fixator. 

Description The fixator is made up of 2 telescopic steel cylinders, an inner threaded bar which is coaxial to the cylinders and a spring which is coaxial to the bar. The opposite ends of the cylinders are closed - except for the hole required for the threaded bar to protrude – and marked by a letter. The cylinder end which is marked by the letter C is threaded, and the threaded bar can be screwed onto it. The end of this cylinder is hexagonal, so that it can be firmly held with a wrench. Compression/distraction can be achieved by acting on this end of the cylinder. The cylinder end which is marked by the letter D has the same di-ameter as the threaded bar which runs inside it. The fixator can be dynamized by acting on this end of the cylinder. The position of the threaded bar which protrudes from the cylinders is adjusted and hold in place by nuts which are screwed onto the bar in a number of 2 on each side. They are numbered with 1 and 2 starting from the one which lies closer to the cylinder end (C1 and C2, D1 and D2) (Fig. 1). 

(Fig. 1)

Static position 
There is no motion between cylinder C and D. To be sure that the fixator is in static position, check that there is clearance between the cylinders, then try to push them one against the other (Fig. 2). 

(Fig. 2)

If there is such motion as to allow the cylinders to come close to each other, the fixator is dynamized, while if there is no motion it is in static position. This should take place in the presence of residual clearance between cylinder C and D. The fact that the two cylinders are in contact does not necessarily im-ply that the fixator is in static position but could simply mean that there can be no motion between the cylinders. If the fixator is already in static position, compression/distraction maneuvers can be performed. If the fixator is not in static position, check that nuts C1 and C2 are uncoupled. This means that they are not tightened to each other, therefore capable of moving inde-pendently, while if they are coupled they are fixed together (Fig. 3). 

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(Fig. 3)

Bring nut C1 in contact with the C end of the fixator until it becomes tightened. Bring nut C2 in contact with nut C1 and tighten it (Fig. 4). 

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(Fig. 4)

Make sure that nuts D1 and D2 are uncoupled, then turn nut D1 until it is brought in contact with the end of cylinder D: keep tightening it until no more motion is present, thus preventing the nut from being further screwed in (Fig. 5). 

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(Fig. 5)

This maneuver must be done gently, stopping when you feel resistance to screwing the nut. Too strong tightening can damage the internal spring, pre-venting its proper operation during the step of dynamization. 
Bring nut D2 in contact with nut D1 and tighten it. This procedure ensures that the fixator is hold in static position. At this point – in order to check whether the procedure was performed correctly – try to push the cylinders one against the other. No motion should occur. 
Compression/distraction 
Fixator compression and distraction should be performed in static position, i.e. when the fixator is not dynamized. 
Distraction 
Nuts C should be uncoupled and removed from cylinder C so that nut C1 is at a distance which corresponds at least to the desired amount of extension of the fixator. Tighten nuts C1 and C2 so as to use them as an anchorage point for threaded bar rotation (Fig. 6). 

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(Fig. 6)

Turn the threaded bar clockwise and hold cylinder C with a wrench to prevent it from turning together with the threaded bar (Fig. 7). 

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(Fig. 7)

The bar should enter into the fixator and became shorter. The central part of the fixator must lengthen accordingly, determining the distraction of the stumps of the fracture to which the fixator is connected in a clinical setting (Fig. 8). 

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(Fig. 8)

Conversely, by rotating the threaded bar counterclockwise, compression can be achieved, provided that there is still motion between the two cylinders. 

Once the desired compression/distraction is achieved, nuts C1 and C2 are uncoupled and brought in contact with the C end of the fixator, then tightened. This makes the desired position to be maintained. To change the position by lengthening or shortening the fixator repeat the previous steps. Dynamization 
Nuts C1 and C2 are uncoupled, brought at 2-3 mm from cylinder C, then cou-pled again. Nuts D1 and D2 are uncoupled, nut D2 should be at a distance from D1 which equals the amount of motion required for dynamization, while D1 is left in its original position, in contact with the end of cylinder D (Fig. 9). 

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(Fig. 9)

Using a wrench, hold the fixator in place by stabilizing the hexagonal portion of the end of cylinder C. Using another wrench, turn the coupled C nuts coun-terclockwise in order to cause the bar to protrude from the cylinder (Fig. 10). 

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(Fig. 10)

You will notice that nut D2 starts rotating with the bar. Once it contacts nut D1, dynamization is achieved and the fixator can make the axial motion given by the distance at which D2 was placed compared to D1 (Fig. 11). 

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(Fig. 11)

Nuts C are uncoupled, brought into contact with cylinder C and then tight-ened. Nuts D1 and D2 are coupled by tightening D2 in contact with D1. The position is stabilized and a dynamized fixator is thus obtained, i.e. a fixator which can move only longitudinally. 
The axial load of the callus in the absence of torsional and bending stresses is considered a proper condition to stimulate its final maturation. 

Radius-ulna

Radius-ulna diaphyseal fracture stabilization by dynamizable fixator.

Tibia

Technique for reduction and stabilization of a diaphyseal tibial fracture by a dynamizable fixator.

Use of the dynamizable fixator

Compresion - Distraction

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