Dyman M. Deformability of systems of means osteosynthesis of extremities taking into account a type of loadings

The method of testing the means of fixation of bone fractures at loads with simultaneous measurement of displacements of fracture points was developed. A non-contact method of digital photography is applied, which allows the recording of spatial displacements of points and does not create additional loads on the object of test. The result of the comparison of the data obtained by the method of digital photography with the data obtained by direct measurement of displacements by the non-contact method using an optical system, showed satisfactory accuracy of the method of digital photography. The discrepancy between the control measurements and the measurements with a calibrated instrument is at (1 ... 4)%. A device for bone loading with systems of osteosynthesis with simultaneous action of axial loading, transverse force and torque was developed and created. The digital displacement measured the spatial displacements of the various fracture points. Methods and programs for testing of tibia, talus, metacarpal and femur bones with modeled fractures and fixation systems have been developed. The characteristics of strength and rigidity of bone fixation systems with fractures and osteosynthesis systems under single and cyclic loads were obtained. In addition, along with the general rigidity of the osteosynthesis system, the spatial displacements of individual fracture points were taken into account. On the basis of the proposed methodology, in Solid Work environment software files based on the finite element method have been created, which allow to estimate the parameters of the stress-strain state of whole and synthesized plates of damaged bones. The developed technique allows to estimate the stress-strain state of bone at different types of fractures and to choose the most stable, optimal system of fixation of the fracture. The criterion ratios were obtained to calculate the levels of loads under which no impermissible displacements and mutual rotations of fracture parts occur. The necessary displacements necessary for the calculations are determined by the results of simple tests with separate action of compression, bending and rotation of bone specimens with simulated fractures and fixation means. According to the results of simple types of loads (compression, bending, torsion), the displacements for plates for fixation of fractures of the tibia are calculated. The levels of allowable loads with the combined action of compression, bending and torsion, and the areas of validity of the permissible loads, are calculated according to the specified displacements. Under the influence of these loads, linear and angular displacements in fractures are within physiologically justified values ​​(mutual displacement within 1 mm, rotation angle within 3 degree). Tests were made to measure the spatial displacements of the most dangerous fracture points under complex loading (compression, bending and torsion). Comparison of test results with calculations performed using simple test data (joint action of joint, bend and torsion) showed a satisfactory coincidence of results. The proposed methods allow accelerated comparative estimates of the rigidity of different osteosynthesis systems on full-scale specimens with simulated fractures.