[MATHEMATICAL MODELING OF OPTIONS FOR MOUNTING AN EXTERNAL FIXATION DEVICE ON THE TIBIA DURING ITS LENGTHENING].

The main problem in the treatment of axial deformities and limb shortening in pediatric orthopedics is the presence of incomplete growth of the patient, which gives an unfavorable basis for the achieved correction. The most advanced technology for the treatment of deformities and limb shortening is the use of external fixation devices (AVF). Target. To study the stress-strain state of the "tibia-AVF model with different variants of AVF mounting in conditions of tibia lengthening. Mathematical modeling of tibial osteosynthesis with external fixation devices in children with achondroplasia was carried out. The model of the distal end of the lower limb contained both lower leg bones and bony elements of the foot. Two variants of the AVF imposition were modeled: with the arrangement of all rods in the same plane, and according to the scheme with a V-shaped arrangement of the rods in the proximal tibia. The values of maximum stresses and values of relative deformations in the elements of the models were investigated. Sweat is a compressive load, the zone of maximum stress (66.8 MPa) in the bone tissue occurs around the upper rod. The smallest stresses (22.8 MPa) are observed around the fourth bar. On the second and third rods, the stresses are the same - 41.6 and 41.5 MPa, respectively. The V-shaped arrangement of the rods leads to a decrease in stresses around the first rod to 57.2 MPa. The stresses in the distal part of the proximal tibia fragment do not exceed 35.5 MPa. Under torsional loads in the model with parallel arrangement of rods, the zone of maximum stresses arises around the first rod (16.3 MPa). The stresses in the distal fragment of the tibia are determined in the range from 1.2 to 3.9 MPa on the lower and upper rods, respectively. The use of an AVF with a V-shaped arrangement of the rods causes stresses in the tibia at a level of 13.1 MPa on the first rod, a minimum 1.1 MPa on the fourth. When the model is compressed with a parallel arrangement of the AVF rods, the values of relative deformations in the bone regenerate are determined in the range from 62 to 85%. The use of the AVF according to the scheme with a V-shaped arrangement of the rods makes it possible to reduce the magnitude of the relative deformations to the level of 77%. In the model with a parallel arrangement of the AVF rods, the relative deformations in the bone regenerate under torsional loads are determined in the range from 3.0 to 6.0%. When using AVF with a V-shaped arrangement of rods, the level of relative deformations is determined in the range from 1.0 to 4.0%. The use of an AVF with a V-shaped arrangement of rods in the lower part of the proximal fragment of the tibia during its osteosynthesis allows reducing the level of stresses at all control points of the model for all types of loading, as compared to the model of an AVF with a parallel arrangement of rods. AVF with a V-shaped arrangement of the rods makes it possible to reduce the values of the relative deformations of the bone regenerate at all the studied control points of the models, both under compression and torsion loads.

[EXPERIMENTAL STUDY OF THE ULTIMATE STRENGTH OF SAMPLES OF MATERIAL BASED ON POLYLACTIDE AND TRICALCIUM PHOSPHATE, PRODUCED BY 3D PRINTING WITH DIFFERENT POROSITIES, DEPENDING ON THE TIME OF HYDRATION].

The advantage of polylactide-based implants is their rapid and complete biodegradation, followed by replacement of the defect with bone tissue. The disadvantage of materials with a high biodegradation rate is their low support ability. The admixture of ceramic materials increases the strength of the implants and reduces the rate of biodegradation. 3D printing technology allows you to reduce the negative factors of ceramic impurities through the manufacture of implants of various porosities. Target. Determine the ultimate strength of a composite material based on PLA and TCP, manufactured by 3D printing with different porosity options, depending on the duration of hydration. Were made 9 samples of material with a size of 10x10x10 mm with different porosity 40%, 30%, 20%. Samples of the material were hydrated in saline. Strength tests were carried out on days 2, 10, and 20 after hydration, 3 samples of material of each porosity. All samples were tested for compression. The carried out comparative analysis indicates that the tested samples are statistically significant (at the level of p <0.05) differ from each other depending on the value of porosity at all periods of hydration. Although the average values of the ultimate strength of samples of the same porosity tend to decrease depending on the period of their hydration, these changes do not acquire statistical significance even between the extreme periods of observation. This is confirmed by the values of the indicator of the statistical significance of the differences p equal to 0.07; 0.759 and 0.124 for specimens with porosity of 20%, 30% and 40%, respectively. The tensile strength of samples of material based on polylactide and tricalcium phosphate, made using 3D printing, directly depends on their porosity, the smaller the pore volume, the stronger the samples. The hydration of the samples in saline solution for 20 days does not entail statistically significant changes in their strength regardless of the pore volume, although the average values of the ultimate strength for all tested samples tend to decrease.

[INFLUENCE OF HIP JOINT CONTRACTS FOR HIPS MUSCULAR].

Objective - to study the effect of hip contractures on the strength of the thigh muscles. Gait analysis was performed in the OpenSim 4.0 program, gait2394 was taken as the basis. Created 4 models with contractures of varying severity. We analyzed the change in the work of the thigh muscles in normal conditions, with adduction, flexion-adduction and flexion-adduction contractures with shortening. According to the data obtained in modeling the adductive and flexor-adducing contractures of the hip joint, it can be noted that contracture changes the work of the muscles around the hip joint. It was noted that modeling only adduction contracture causes noticeable changes in the medial group of femoral muscles and muscle stabilizers. Of the muscles of the posterior thigh group, m.semimembranosus, m.semitendinosus and m.biceps femoris are most susceptible to changes. These muscles change the level of load, and most importantly, periods of excitation and muscle relaxation shift. Simulation of combined flexion-adduction contracture showed that muscle dysfunctions increase, and m.sartorius, an anterior thigh muscle, was added to the muscles in which noticeable changes additionally occurred. With simulated adduction and flexion adduction contractures, changes occur in all the muscles of the thigh, periods of their excitement and relaxation shift, but the level of muscle tension is close to normal values - not exceeding them by 20-30%. Flexion-leading contracture with shortening of the limb leads to a distortion of muscle parameters in the form of excessive loads for the step (up to 100-300%). Based on the obtained simulation results, the inability of the muscles to develop the necessary efforts leads to a change in the parameters of the step in the form of a decrease in the length of the step and the duration of the periods of support on the foot, a change in the nature of the transfer of the foot. It is logical to assume that a long period of impaired muscle function will lead to the development of sustainable changes in the walking pattern.

Review: the Caspian Sea benthos: unique fauna and community formed under strong grazing pressure.

A quantitative comparison of the benthic distribution in the Middle and Southern Caspian Sea, using benthos distribution maps with previously published materials, showed that the benthic communities is stable and interrupted only by the introduction of new species. The bottom community is dominated by small-size organisms, mainly fry and young and the benthic biomass is low although its efficiency as prey for higher trophic levels is high even though carnivores are almost absent in the bottom community. At depths of c.100 m the benthos biomass and species diversity sharply decreases showing these features as a unique case of a bottom fauna and bottom community formed and modified under the influence of a severe grazing pressure by the sturgeon (Acipenser spp.) during very long periods. It is therefore suggested that grazing pressure has become the most important forcing function for the diversity and development of the bottom community.