Musiienko O. Strength and deformability of osteosynthesis systems taking into account the properties of damaged bone tissue and its artificial substitutes

The dissertation is devoted to the study of the deformability and strength of osteosynthesis systems used in modern surgical practice for fixing gunshot and traumatic fractures of human bones: determination of the mechanical properties of bones under various conditions of loading, deformation and development of displacements in fractures under the action of short-time loads, taking into account the degradation and regeneration of bone fabrics. A technique was developed and equipment was created for measuring the degree of bone tissue degradation in the area of a gunshot wound, which is used to determine changes in the mechanical characteristics of bone tissue in linear areas of deformation. New methods of research on the strength and deformability of osteosynthesis systems for traumatic bone fractures are described, which take into account the characteristics of bone tissue, including its degradation in gunshot fractures and the development of regenerative bone tissue in the process of fracture fusion. New schemes for fixation of StAZF are proposed, which are aimed at improving the effectiveness of the course of treatment of gunshot and traumatic fractures. The mechanical properties of bone tissue were calculated and the anisotropy of bone tissue characteristics was confirmed on the basis of experimental studies. The ratio of the modulus of elasticity in the direction of osteon orientation to the modulus in the direction perpendicular to the osteon orientation ranges from 1.14 to 4.02. Anisotropy of bone tissue behavior is also observed during relaxation and creep. It has been experimentally confirmed that the degree of wetting of the sample strongly affects its mechanical characteristics. Therefore, to obtain more reliable data, samples of bone tissue after extraction from the human body should be stored under conditions similar to those present in the human body. On the basis of experiments and calculations, it has been proven that bone tissue is a non-linear viscoelastic material. The dependence of the mechanical properties of bone tissue on their X-ray density has been determined, which makes it possible to create computer models with maximum approximation of the results to real ones. Modeling surgical intervention and predicting its results, using such models, allows to reduce the frequency of errors and complications in the reconstructive and restorative treatment of patients with the consequences of ankle joint damage. It was established that the area of bone tissue damage during a gunshot fracture reaches 40 mm from the fracture site, and changes in stiffness are up to 20% of the stiffness of an intact bone, which must be taken into account when securing rod devices for external fixation of fractures. It was determined that increasing the angle of inclination of the rods increases the stiffness of the system during compression, bending and torsion. A rational location of the rods is proposed, which takes into account the presence of areas of bone tissue degradation and compensates for the loss of stiffness in the case of a gunshot fracture. The deformation of the "bone with a fracture - a means of fixation" system at the stages of bone tissue regeneration under the action of compression and bending was studied. It was established that the formed regenerate significantly increases the stiffness of the system "bone with a fracture - bone regenerate - means of fixation" and the level of permissible loads on the system. The possibility of using polymer substitutes for regenerated bone during experimental bone research has been proposed and confirmed. A mathematical model was developed to take into account the contribution of the regenerate to the mutual displacements of the fracture points and to estimate the permissible loads on the bone. The levels of permissible loads that can be applied to the limb are calculated, taking into account the known permissible mutual displacements of the fracture points. The rigidity of systems in volumetric, rod and beam structures was compared. The coincidence of the experimental results with the results of computer modeling in the ANSYS Workbench software complex is shown. It has been confirmed that the system with distant rods has the lowest stiffness, and the scheme with the rods arranged at an angle of 60° has the highest. A working mathematical model was obtained for the study of other load cases that cannot be investigated by experimental methods. The results of the work - the methods and data of mechanical tests, the results of computer simulation - can be used to improve the methods of treatment of damaged limbs at the intermediate and final stages of fracture fusion.