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Dynamizzable linear system 

Instruction for use 

Important note 
Please read carefully the following instructions before applying the Dynamizable system on clinical patients. This is a veterinary surgical device, and requires knowledge of its use and limitations. No attempts should be made to use the device for indications different from those the system was developed for. Any improper use will be under the responsibility of the user. 
Description 
The Dynamizable system is an external linear fixation system designed to stabilize fractures in dogs of body weight between 10 and 30 kg. Its peculiar feature, which makes it unique among the veterinary external fixators, is that it allows to perform compression and distraction on the fracture, as well as the dynamization of the bone callus. As usual for external fixation, the addition of pins and changes in the frame structure may profoundly affect the biomechanical properties of the fixator, allowing its use in heavier patients. Being almost impossible to describe all the po-tential variations of the fixator features that can influence its biomechanical proper-ties, it is the surgeon's experience to dictate the patient's weight that fits with a specific frame configuration. 
Kit components 


The Dynamizable kit contains the following components. 

  1.  Sterilization case (Code C00040010a)

  2. One external linear dynamizable fixator 10 cm (Code F00030001b)

  3. One external linear dynamizable fixator 15 cm (Code F00030002b)

  4. Six clamps for dynamizable fixator (Code M00010018a)

  5. Two extensions for dynamizable clamp (Code E00010001a)

  6. Four threaded pins ø 2.8 mm L 120 mm (Code F00020161a)

  7. Four threaded pins ø 3.5 mm L 130 mm (Code F00020162a)

  8. Four caps for pins ø 2.8 mm (Code P00040005a)

  9. Four caps for pins ø 3.5 mm (Code P00040002a)

  10. One hexagonal wrench 3.0 mm with spherical tip (Code U00010002a)

Suggestions for use and reuse of the components 

  1. Sterilization case. Always perform the sterilization cycle with the cover closed. If left open, it can be bent or damaged during the cycle. The case should be sterilized within a standard sterilization bag, because it is not in-tended to maintain sterility of the content once it’s withdrawn from the auto-clave. The case is reusable up to ten sterilization cycles. It is possible to do more cycles, but this is not recommended, and it is up to the user's judgment and responsibility.

  2. Linear dynamizable fixator 10 cm. It can be sterilized as many times as re-quired. It can be used on clinical patients many times, but its mechanical func-tion should be checked for each use. To increase its life span, it is suggested to send it about once a year to the Ad Maiora assistance center, depending on the number of sterilization cycles received, to change the parts subjected to wear.

  3. Linear dynamizable fixator 15 cm. The same as for point 2.

  4. Clamps for dynamizable fixator. They can be sterilized as many times as re-quired and can be reused on clinical patients. It is strongly recommended, though, to check every component after the mechanical loading during the clinical use, because if the more delicate parts, like threads, are damaged, their biomechanical behavior is unpredictable, posing a serious risk for further clinical applications.

  5. Extensions for clamps. The same as for point 4.

  6. Threaded pins ø 2.8 mm L 120 mm. They can be sterilized as many times as requested, but they cannot be reused on clinical patients.

  7. Threaded pins ø 3.5 mm L 130 mm. The same as for point 6.

  8. Caps for pins ø 2.8 mm. They cannot be autoclaved, and they should be ap-plied to the protruding stump of the pin at the end of the surgery. They can be used until they are efficient in protecting the pin stump.

  9. Caps for pins ø 3.5 mm. They cannot be autoclaved. The suggestions for use are the same as for point 8.

  10. Hexagonal wrench ø 3,0 mm with spherical tip. It can be sterilized as many times as requested, and discarded when it is damaged or no more func-tional.

Instruments not included in the kit 

  1. Dedicated drill bit for predrilling for threaded pins ø 2.8 mm

  2. Dedicated drill bit for predrilling for threaded pins ø 3.5 mm

  3. Combination wrench 8,0 mm


These instruments can be sterilized as many times as requested, and discarded on-ly when damaged or no more functional. It is important, though, to always use sharp bits, because if it is dull the bone is damaged and heated during its perforation, with the potential risk of bone necrosis and subsequent pin loosening.

General considerations on the use of the Dynamizable system 
Number and type of pins 

The pins provided in the kit are purely indicative of the range of pins available for the patients the kit is intended for. Four units for each of the above-indicated pins are provided, but the surgeon can choose to include in the kit more pins of a specif-ic type, thanks to the empty holes in the support. For example, for bigger patients the use of 4.5 mm threaded pins (Code F00020163a, not provided in the standard kit configuration) could be more appropriate. Please note that Ad Maiora cannot be considered responsible for problems related to instability of the fixator due to the use of pins from different producers or for improper use of the pins provided.  


General rules for pin application to the patient 
Threaded pins ø 2.8 L 120 mm and 3.5 mm L 130 mm (Codes F00020169a and F00020162a). 
They represent the major holding tool for the fixator, and should be used as the primary mean for connection of the fixator to the bone. A stab wound is performed in soft tissues, and they are slightly dissected by a scissor or a mosquito forcep. Then, a sleeve is inserted in the wound and steadily hold orthogonally to the bone surface. A 2.0 mm drill bit for the pins ø 2.8 mm F00020169a or 2.5 mm for the pins ø 3.5 mm F00020162a is used to perforate the bone. It should be inserted at a max-imum speed of 500-600 rpm, and continuously chilled by saline flushing during insertion, to avoid heating of the bone, which can induce osteolysis, and secondary pin loosening. The drill bit is retracted while holding the sleeve in place. The thread-ed pin is inserted by hand, using a chuck as a driver for insertion. When the surgeon feels the resistance of the far cortex, the insertion should be continued just until the feeling of resistance stops, adding a couple of turns. The pin is released from the chuck, and any tension on soft tissues should be released by enlarging the wound. The same principles apply to the use of the 4.5 mm threaded pins (Code F00020163a). 

 

Setting of the clamp for the connection of the pin to the fixator's body 
For a correct sequence of the clamp setting please refer to the pictures that come with this guide. 
Clamp for dynamizable fixator (Code M00010018a) (Fig. 1). It is intended for the connection of a threaded pin to the dynamizable fixator. The clamp is connected to the fixator's body by the hole (a) with a close clamp but with the tightening screw (b) released. In case it is necessary to put a clamp in between two clamps already tighten, it is possible to remove the tightening screw (b), opening the clamp in two parts (half-clamps), then putting the open clamp on the fixator's body and tighten-ing the screw (b) again. Please note that the tightening screw (b) should be inserted first through the gliding hole on the first half-clamp, and then screwed into the threaded hole for traction in the second half-clamp. To avoid that an excessive ten-sion is applied on the screw (b), which could open the branches of the clamp on the opposite side, a spacing plate (c) should be put on the opposite side of the clamp. A pin or extension can be inserted through a hole (d), which can accommodate a threaded pin up to a ø 4.5 mm or the shaft of the extension E00010001a. In both cases, locking in the desired position is achieved by means of the locking screws (e). The difference between inserting the pin or the extension in the clamp is due to the fact that inserting just the pin directly in the clamp it is possible to translate it along or rotating it around the fixator's major axis (Fig. 2). Instead, if an extension is connected with the clamp, and the pin is inserted through the extension, it is possi-ble to incline it along the longitudinal axis of the fixator (Fig. 3). Furthermore, the ex-tensions allow a translation orthogonal to the fixator's major axis, so that the pin can be actually moved on four planes. 
The extension is locked to the clamp by the locking screws (e), and locks the pins into a hole in the extension's head by a locking screw. All the screws of the clamp and the extension can be turned by the hexagonal wrench ø 3,0 mm with hemi-spherical tip code U00010002a that is enclosed in the kit. 
The head of the extension E00010001a should always be positioned on the side of the clamp opposite to the locking screw of the clamp (b), to avoid any interference between them during intraoperative maneuvers. 

Use of the fixator for compression/distraction and for dynamization 
The most peculiar feature of the Dynamizable fixator is the possibility it offers to perform maneuvers on the fracture area. In the acute phase of treatment micromet-ric compression and distraction can be performed, useful for fracture reduction. In the more advanced phase of bone healing, dynamization can be performed. It al-lows stimulating the bone callus by axial compression forces, preventing those of bending and torsion. Some suggestions for the use of the fixator for fracture reduc-tion and stabilization are given underneath. It should however BE

 

STATED VERY CLEARLY THAT: 

  1. They represent just some suggestions on the potential use of the fixator, and they are not intended as a clinical indication for its use, which pertains to the choice of the surgeon, and must be based on clinical evaluation of the patient and of the fracture features.

  2. As usual with external fixation, many different frame configurations and choice of pins and their positioning are possible. For this reason, a unique recom-mendation cannot be made for a specific fracture, but just general principles that can be applied.

  3. So many variables can affect the final outcome of a treatment, including post-operative management of the patient. It is the responsibility of the surgeon to verify those variables, and to provide all the personnel and owners with pre-cise instructions on how maintain the fixator, check its status, and manage the postoperative care in a correct way.

Compression/distraction 
The fixator is made by two metallic cylinders (cylinder D and cylinder C) that are tel-escopic in their central part. The inner space of the cylinders is occupied by a threaded bar, with two hexagonal nuts at each extremity (nuts D1 and D2 on the ex-tremity D, C1 and C2 on the extremity C). The extremity of the cylinder C has a hexagonal shape, like a nut, to allow for its stabilization by a wrench n. 8 (not included) (Fig. 4 A). 
To perform compression/distraction, the fixator should be in static position, and dy-namization mechanism should be locked. To check for the fixator's state, i.e. static or dynamized, holding each cylinder by one hand, push each one against the other. If the cylinders shift on each other it means that the fixator is dynamized. On the contrary, if it stays stable it is in static position. In this latter case the fixator can be used for compression/distraction. In the former case it should be locked following the next steps. 

  1. Bring the nut C1 close to the extremity of the cylinder C, stabilizing the ex-tremity by a wrench n. 8. Tighten the nut C1 against the extremity C of the fix-ator.

  2. Check that the nuts D1 and D2 are disconnected. Holding the fixator by a wrench n. 8 on the extremity C turn the nut D1 clockwise by another wrench n. 8, in this way compressing it toward the center of the fixator (Fig. 4B).

  3. Stop the compression of the cylinder as soon as the resistance is felt to rise. Now, doing again the compression of the fixator's cylinders by hand, it should be static (Fig. 5 C). IT IS IMPORTANT not to exert too much compression by the nut D1, because this could be damage the internal spring, making the later dynamization impossible.

  4. Lock the static configuration of the fixator by tightening the nut D2 against the nut D1.

  5. It is now possible to use the fixator for compression/distraction. When a dis-traction is scheduled, as usual in the early phase of fracture reduction, discon-nect the nut C1 from the extremity C of the fixator, bring it together with the nut C2 to the extremity of the threaded bar, and tighten them together. Hold-ing the fixator by a wrench n. 8 on the extremity C, turn the threaded bar in a counterclockwise way (it should exit from the fixator's body) using as a holding point the couple of nuts C1-C2. Keep turning until the central part of the fixator is 1-2 mm large. In this way it will be possible to exert a distraction on the frac-ture area correspondent to the length of the threaded bar out of the fixator body (Fig. 5 D). When a compression on the fracture area is needed, the fix-ator should have the threaded bar completely inserted in the fixator body by turning it in a clockwise direction, and the central part of the fixator about 25 mm open. In this way it will be possible to exert compression on the fracture area correspondent to the length of the central area of the fixator (Fig. 6 E). 

Use of the fixator for fracture reduction and its stabilization 
Generally speaking, long bones fractures will present a dislocatio ad longitudinem with dislocatio ad latus. Fracture reduction is then achieved distracting the fracture segments, in order to reestablish the original bone length and to allow for realign-ment. Fracture reduction can be achieved following the next steps. 

  1. Insert in each fracture segment JUST ONE PIN of correct size. Connect each pin to a clamp with extension, and tighten all the locking screws of the fixator so that the overall frame is stable (Fig. 6 F).

  2. Holding the fixator by a wrench n. 8 on the extremity C, use another wrench n. 8 to turn the nuts C1 and C2 tightened together in a clockwise direction (the threaded bar should go into the fixator's body) (Fig. 7 G). In this way, the cen-tral part of the fixator lengthens and the fracture is distracted.

  3. Once the distraction is large enough for the fracture segments not being over-lapped, it is possible to perform the maneuvers for fracture reduction (Fig. 7 H). Releasing the locking screws of the extension it is possible to correct rota-tion on the minor axis of the bone segment and translation ad axim, while re-leasing the locking screw of the clamp it is possible to correct translation be-tween the fracture segments. It is important to notice that the correction of torsional deformities in never possible with linear fixation, and then specific at-tention should be paid when the first pins are inserted in the fracture seg-ments, in order to avoid this kind of deformity.

  4. Once fracture reduction is achieved, it is possible to exert a moderate com-pression between the fragments if the fracture is transverse or short oblique (Fig. 8 I).

  5. It is then possible to add pins for further fracture stabilization (Fig. 8 L). The clamps needed for adding pins can be prepositioned on the fixator's body if already scheduled in order to speed the procedure up, or opened and inserted in the requested position even in a later phase. It is important that in this phase the fixator stays in a static position, and for this the nuts C1 and C2 should be released, C1 is tightened against the extremity C of the fixator and C2 against C1. This position is the one that will be used for the management of the first phase of bone healing. 

Use of the fixator for the dynamization of the bone callus 
Dynamization is different from destabilization of the fracture because it selects the forces that will load the bone callus while maturing. The callus is loaded by axial compression forces, which are considered positive for its maturation, excluding tor-sion and bending, potentially dangerous for the callus. 
The dynamization procedure should be performed only on calluses radiographically visible, vascularized and extended to the majority of the fracture area. Do not dy-namize atrophic or too early calluses. 
The steps to achieve dynamization of the fixator are the following. 

  1. Release the nuts C1 and C2, bringing them away from the extremity C of the fixator, and then tighten them together again.

  2. Release the nut D2 while holding the nut D1, and bring it away from D1 of a couple of mm. The distance between these nuts represents the amount of the dynamization introduced in the system.

  3. Turn the nuts C1 and C2 tightened together in a counterclockwise direction
    (the threaded bar should exit from the fixator), holding the fixator by a wrench
    n. 8 on the extremity of the cylinder C, until the nut D2 contacts the nut D1 and stops turning. Stop the turning of the threaded bar at this point.

  4. Tighten together the nuts D1 and D2 to keep the dynamization as set.

  5. Release C1 from C2, bring C1 back in contact with the extremity C of the fix-ator and tighten it, and then tighten C2 against C1 to lock the fixator in the new dynamized position. The fixator will now let the axial loads to pass through the fracture area, and this will stimulate the callus maturation (Fig. 9 M).

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