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Especially in adult horses the treatment of radial fractures turns out to be difficult and carry a guarded prognosis.A high amount of energy is necessary to destroy the bone. That"s why the fractures are often comminuted and accompanied by severe soft tissue trauma. Besides open fractures are not uncommon. These circumstances lead to circulating interruptions and an increased risk of wound infection.Yet the external fixation is convenient for the treatment of open, compound and infected fractures with extensive soft tissue damage in human and small animal medicine, the possibility of application to radial fractures in horses should be tested. In order to recreate the conditions occured in vivo we chose an unstable fracture model.The circular external fixator showed greatest stability and variability of all external fixations. In an in-vitro study load investigations on six varying Ilisarow ring fixators were performed.Three different ring diameters (140 mm, 180 mm, 200 mm) with either varying pin diameter (4-6 mm) or amount of the pins or rings respectively were investigated in continuos loading tests.Compression- and bending stiffness could be analyzed in single- and continuos-compression modes with a material testing machine. The previous performed single loads were used to determine the index for the testing forces, which resulted in a movement within the fracture gap of approximately 5 mm. Indices of the same level were used for the continuous loads as well.Every fixator took an examination in 100.000 axial compressions and 1000 bending loads. The bending stiffness were calculated by employing the principles of four-point-bending. The examination of the axial stiffness was made on fixator-bone-compositions, in difference to the bending stiffness investigations, where fixator-aluminium-units have been brought in. In in-vivo applications the chosen ring diameter depends on the maximal diameter of the soft tissue around the sector of the radius. The ring diameter should be 1-2 cm larger than the covering soft tissue diameter to prevent complications associated with soft tissue swelling and on the other hand to create stability as high as possible. The external fixator constructions Nr.1 and Nr.4 with 140 mm rings show that the extending of the pin diameter from 4 to 5 mm increases the axial stiffness to 54% and the bending stiffness to 59,6%. The body weight of the horses, within the fixation can be brought in, is calculated as 190 and 295 kg. Employment at radius fractures in foals and ponies of small races seems possible.Increasing the pin diameter from 5 to 6 mm in identically frame constructions in the fixation device Nr.2 and Nr.5 rises the axial stiffness to 43% and the bending stiffness to 31,6%. The use in yearlings and horses of small races with a maximal body weight of 275 and 390 kg is considerable.Multiplying of the ring amount from 4 to 6 and therefore the amount of rings from 8 to 12 in the construction Nr.3 and Nr.6 increases the axial stiffness to 26% and the bending stiffness to 60%. On condition that the soft tissue attached to the radius has no greater diameter than 180 mm, these fixations could be applied in all horses with a maximal body weight of 330 and 415 kg.The raised forces occurring while getting up in the box should be considered. Uncontrolled movements while waking up after anaesthesia can release extreme forces, which can lead to failure of every fixation construction.The study demonstrates the high stability of the Ilisarow ring fixators. The results represent as well, that the stiffness and depending on that the
strengths of the tested fixators is not sufficient to manage radius fractures in adult horses. The devices could not resist the acting forces in necessary measure. Extensive interfragmentary movements with negative effects in view of the fracture healing would occur.A gain of stability could be reached especially by enhancement of the rings, the connecting bars, the pins, pretension of the transfixation pins and improvement of the pinarretation.With modified ring fixator systems the treatment of radius fractures in adult horses could surely be possible. The postnarcotic phase should get special attention and specific measures should be enforced to reduce the uncontrolled movements.