Журнал «Травма» Том 15, №5, 2014

Introduction. Creation of the most stable fixation of bone fragments, providing optimal mechanical conditions for early consolidation, is the main task in case of transosseous compressive osteosynthesis.

The stability of an external fixation device is directly influenced by the diameter of supports. Reduction of distance between the points of needle fixation increases the overall rigidity of the whole structure. A similar trend is typical for all systems of external fixators. The closer the frame components are located to the bone – the more stable such a structure. 

The geometry of an external support is one of significant components of transosseous osteosynthesis biomechanics at the present stage of its development. Most well-known devices of external fixation are designed on basis of ring bearings. A number of devices with oval, square, hexagon and other shapes of supports have been also worked out and clinically implemented. The authors’ search is obviously connected with imperfection of ring bearings, the shape of which does not match the anatomic form of segments and does not meet all the requirements, faced by the method of transosseous osteosynthesis.

Objective: biomechanical grounding of reasoned application of a universal device with adaptation of supports shape to anatomical configuration of a segment.

Material and methods. Using the program “Autodesk Inventor 11” and the finite element method, the three-dimensional computer simulation of biomechanical systems of two models was performed:

I - "tibia - Ilizarov's device with eccentric location of supports";

II - "tibia - universal device with shape, adapting to configuration of extremity segment".

According to the method of transosseous modules research, the device layout was chosen by the type of a combined tertiary module, in which a combination of needles and rods shall be used as transosseous elements.

Results and their discussion. In order to perform a comparative analysis of different systems of external fixation, all calculations were made using the general schemes of fixing and loading of simulated systems. The tibia consolidation was fulfilled on the epiphysis face of the proximal fragment. The loading vectors were applied to the distal fragment of bone in six standard degrees of freedom. The main objective of research was determining the load in various directions, characterized with one-millimeter shift of the distal fragment, which is considered critical.  

Regarding to the results obtained, one-millimeter shift of the distal fragment in model II occurs, when the loading, applied along the Y-axis, is 1194N, along the X-axis – 495N, along the Z-axis – 465N and the moment of force along the Y-axis – 215Nm, in comparison with model I it is correspondingly higher by – 55,47 % (768N), 15,65 % (428N), 12,05 % (415N) and 26,47 % (170Nm).

Conclusion. The universal device, developed for transosseous osteosynthesis, owing to possibility of adaption of supports shape to anatomical configuration of a segment, the rigidity of fragments fixing, if compared with llizarov’s device, is higher by 55,47 % when applying compression forces, by 12,05-15,65 % - when applying transversal forces, and by 26,47 % - rotary shifting forces. This makes it possible to apply early loading to a damaged limb, thus apparently allowing to optimize the terms and anatomic-functional results of curing patients with tibia fractures.