MECHANICAL AND CLINICAL CHARACTERISTICS OF THE «ROD – BONE» CONNECTION IN TREATMENT OF GUNSHOT FRACTURES WITH EXTERNAL ROD DEVICES FROM VARIOUS MANUFACTURERS

Abstract

Objective. To find out the state of the bone threading under the conditions of inserting the rods of different manufacturers and to establish the duration of a stable «rod – bone» connection in treatment of diaphyseal fractures of the bones of the limbs. Methods. An experiment was conducted using tibia bones of calves. Rods used in external fixators of Biomet (France), Stryker (USA), LLC H B Orto (Ukraine), ORTOPAK (Ukraine) manufacturers were selected. The shape of the bone threading and its contact with the surface of the rod were studied at 2‒5X magnification. Devices from the specified manufacturers were used to fix bone fragments during the treatment of gunshot fractures in 91 patients. The stability of the rod in the bone was checked. Results. The experiment showed that in order to obtain the appropriate bone threading, it is necessary to first pass through both layers of the compact bone of the diaphysis using a drill with a diameter that corresponds to the inner diameter of the threaded part of the rod. Without this, bone coils in the first cortical layer are destroyed or bone fragments in the second are chipped off, reducing the strength of fixation. In the case of screwing the rods into the drilled channel in the second layer of the cortical bone, the quality of the «rod – bone» connection was worse in all cases. Under the conditions of installing the rods in the cancellous bone, a larger number of defective turns was formed in it compared to the compact one. The lowest frequency of rod instability in patients was found when using the ORTOPAK device (18 %); it was much more frequent (35– 51 %) when using devices from other manufacturers. The incidence of the unstable state of the rods was almost 4 times greater in their location in the epimetaphysis than in the diaphysis. Conclusions. For the most effective connection of the rod with the bone, it is necessary to screw it into the prepared channel with a diameter that corresponds to the inner diameter of the threaded part of the rod. The quality and duration of the stable state of the rod in the bone depends on the technical characteristics of its threading, localization and state of fusion of the fragments.