P. 584

An Urban Experience
purchase can be obtained by engaging the sacrum through the ilium when applying a lateral bone plate in dogs, especially after pelvic osteotomy. Increased bone purchase might lead to less pelvic canal narrowing. However, clinical studies evaluating the bene t of this increased screw purchase have yielded con icting data. In the only study available involving cats, engaging
the sacrum during lateral plating of the ilium did not signi cantly affect screw loosening or pelvic narrowing.
In the presented study in only 1 of 3 cats with screw loosening in the cranial fragment, the screw purchasing the sacrum was loose. Screw loosening was not associated with concomitant contralateral or ipsilateral fractures however this might be underestimated due
to the small number of cats in each group. Despite the limitations, this is the  rst study investigating locking plate for ileal fractures in cats. In conclusion, less screw loosening but no signi cant difference for narrowing of the pelvic canal was observed in lateral plating of feline ilial fractures with an LPS compared to lateral plating with DCP. Implant failure occurs due to screw loosening and not due to failure of the plate.
In some cases conventional plates, or combination plates that allow both locking and compression (LCP, ALP), are an appropriate choice. In most cases a simple fracture should be treated with the goal of absolute stability
using a compression device. Both DCP and LCP are appropriate choices because they allow interfragmen- tary compression. Metaphyseal fractures can be  xed with anatomically pre-shaped plates with locking holes. However, if the plate is not pre-shaped and the locking holes are not placed according to the anatomical region, a conventional plate allows more precise placement of the screws.
The selection of the appropriate length of the plate is a very important step in the preoperative plan. The plate length depends on the fracture pattern and the function that the plate is intended to serve. To maximize implant stability in bridging plating, long plates with fewer screws should be used to decrease the lever arm and distrib- ute the bending forces. The number and position of the screws is a major determinant of the stability and the me- chanical properties of the construct. Two screws in each main fragment are the minimal number required to main- tain the bone-implant construct from a purely mechanical point of view. However, loosening of one screw will cause overloading of the other screws, resulting in failure of the whole construct. By increasing the number of screws there is a decrease in the magnitude of load on each screw, and therefore a reduced risk of pull-out. However, more screws weaken the bone. Hence, it is important to  nd a balance with the appropriate number of screws. It is generally recommended to use three screws on either side of the fracture against bending, and four screws per fragment against torsion.
The position of the screws in uences the stiffness of
the bone-implant construct and stress distribution in
the plate. Minimizing the distance between the nearest screws on either side of the bone fragments (also called working length) increases stiffness and reduces gap motion at the fracture. With a short working length the stress is concentrated and there is higher risk of implant failure from cyclic fatigue of the short segment with concentrated stress. When the innermost screws are further away from the fracture site, the working length
of the plate is greater, allowing bone deformation, gap motion and better distribution of stress in the plate. To achieve a greater working length and a suf cient number of screws on either side of the fracture it is necessary
to use long plates. Considering that on each side of the fracture there should be three screws and two empty holes, plates of 10 holes or more should be used most of the time.

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