MATHEMATICAL JUSTIFICATION OF THE CHOICE OF RODS FOR EXTERNAL FIXATION DEVICES FOR POLYSTRUCTURAL PELVIC INJURIES.

Aim - In order to fulfill the purpose of biomechanical substantiation for extrafocal pelvic osteosynthesis in osteoporosis we studied the stress-strain state (SSS) of LEG under conditions of external fixation by apparatuses with cylindrical and conical rods. Studies of the stress-strain state of the lower extremity belt by the finite element method were carried out under conditions of external fixation by devices with cylindrical and conical rods. In the finite element method, the approximate solution is constructed as a superposition of approximating functions. At the first stage of solving the problem, the object is divided into areas of a simpler form - finite elements whose geometric dimensions are significantly smaller than the dimensions of the entire biomechanical system. Modern software systems generate finite elements of the grid automatically using elements with triangular faces in most cases. At the junctions of the elements (nodal points), the real stress field is replaced by the action of forces and movements. The type of finite elements is characterized by the number of nodes and the degree of approximation of unknowns within the domain and largely determines the accuracy of the resulting solution in the finite element method. Various types of biological tissues were taken into account in the conducted studies: compact and spongy bone, cartilage tissue, intervertebral disc, ligaments. In this study, the material was considered homogeneous and isotropic. The main load is body weight. In the calculation, the body weight was taken to be equal to 700 N. The geometric model was built on the basis of tomographic sections of the pelvis carried out through 0.5 - 1 cm for irregular zones. A pelvis with rotationally unstable (type B1 according to AO classification) damage after osteosynthesis by an external fixation device was modeled in the variants of using cylindrical and conical rods. Mises stresses were used to assess the stress state. The resulting model consists of 75,845 finite elements and has 132253 nodes. The construction of the geometric model was carried out in the SolidWorks program. VAT calculations and analysis were carried out in the ANSYS program. In the first variant of the study of the pelvic model with normal bone tissue and cylindrical rods, the calculation results showed that with a single support standing (support on the left limb), the supporting side with pronounced stress concentration zones in the sacroiliac joint, the place of entry of the rod into the bone and in the area of reducing the thickness of the iliac wing is more tense. Two stress concentration zones are observed along the passage of the rod. The most intense is the area of the screw entry into the bone (18.5 MPa). There is also an area of increased stress at the site of a decrease in the thickness of the iliac wing (8.1 MPa), where the rod passes closest to the cortical layers. The calculation of the model using conical shaped rods showed that the nature of the VAT distribution for the model as a whole has not changed, and the stress state level has decreased. So, at the point of entry of the screw into the bone, the value of the Mises stresses is 16.4 MPa, and at the point of reduction of the thickness of the iliac bone - 6.3 MPa. It is worth noting that the area with an increased stress state along the passage of a conical rod is smaller than for a cylindrical one. In the second variant of the study for a pelvic model with osteoporotic bone tissue, a comparative analysis of VAT when using cylindrical rods of an external fixation device showed that the general nature of the distribution of stresses and deformations for the model as a whole did not change, but the VAT level increased. At the point where the screws enter the bone, it is 28.4 MPa, at the point where the thickness of the iliac wing decreases - 9.1 MPa. The level of tension has also increased throughout the "rod-bone" contact. A comparative analysis of VAT for the variant of conical rods of the external fixation apparatus and osteoporotic bone tissue showed that the general nature of the VAT distribution for the model as a whole has not changed, and the level of stress state has increased as well as in the model with cylindrical screws. At the point where the screws enter the bone, it is 26.5 MPa. At the site of the reduction in the thickness of the iliac wing, the stress level is 7 MPa. The use of conical shaped rods in the external fixation device of the pelvis makes it possible to reduce the level of stress-strain state both in the area of the entry of screws into the bone and in the area of the thinnest part of the iliac wing. For external osteosynthesis of the pelvis in polystructural injuries, lowering the stress state when using conical rods plays an important role, since the strength characteristics of osteoporotic bone tissue are significantly lower than those of normal. Thus, the use of conical rods in external pelvic fixation devices improves the strength characteristics of the "pelvis - rod" system, which makes it possible to recommend their testing in clinical practice.

[Clinical features and prognosis in heart failure patients with chronic obstructive pulmonary diseases].

BACKGROUND: Multimorbidity is a specific characteristic of the modern patient with chronic heart failure (CHF) which significantly changes clinical course, prognosis of the syndrome, leads to socio­economic losses and makes significant adjustments to treatment tactics. The goal is to study the clinical features and prognosis of patients with CHF in combination with chronic obstructive pulmonary disease (COPD). MATERIALS AND METHODS: We studied 183 HF patients, including with stable CHF, including 105 with CHF combined with COPD. The clinical phenotype was assessed by its belonging to the functional class and the severity of COPD. A 6­minute walk test (6­MWT), spirometry, echocardioscopy, testing on a scale assessing the clinical condition, quality of life were studied. The end points during the year were: all­cause mortality and cardiovascular mortality, myocardial infarction, stroke, pulmonary embolism, and hospitalization rates due to acute decompensation of CHF. RESULTS: The clinical phenotype of CHF combined with COPD was characterized by a high frequency of smoking, low quality of life and exercise tolerance. Respiratory dysfunction in CHF in combination with COPD was characterized by mixed disorders (68.4%), in CHF without lung disease, restrictive (25.6%). Cardiovascular mortality in comorbid pathology was 4.0%, in CHF without COPD - 4.6%; myocardial infarction was observed 1.7 times more often with lung disease than in patients with CHF only (16.8% and 10.8%); stroke was observed exclusively in comorbid pathology (8.9%). The combined endpoint (all cardiovascular events) with CHF in combination with COPD was achieved 2.3 times more often in comparison with patients with COPD only (29.7% and 15.4%). Hospitalization due to acute decompensation of CHF occurred 2 times more often with CHF in combination with COPD than without it (32.7% and 15.4%) with a tendency to increase as the left ventricular ejection fraction decreased. CONCLUSION: The results of the study demonstrate that COPD contributes to the formation of the clinical phenotype of CHF from the standpoint of the mutual influence of the characteristics of the cardiovascular and respiratory systems, and also aggravates the prognosis that requires an integrated approach to the differential diagnosis and individualization of pharmacotherapy.

[Family History of Cardiovascular Disease in Patients With Early Development of Acute Coronary Syndrome].

The aim of the study was to analyze clinical features of patients with premature acute coronary syndrome (ACS) in relation to family history of cardiovascular disease (CVD) and familial hypercholesterolemia (FH). MATERIALS AND METHODS: Of 2832 patients included in ORACUL 1 and ORACUL 2 multicenter observational trials 512 pts who developed premature ACS (≤55 years for men, ≤60 years for women) and had known family history and LDL level were selected for this study. Of these patients 297 had positive family history (51 with FH, 246 no FH), 215 had negative family history. RESULTS: Among patients with positive family history there were more women (31 vs 20.9 %), while among patients with negative family history there were more men (79.1 vs 69 %). The fact of regular alcohol consumption was significantly more frequently observed among patients with positive family history but without FH, compared to patients with positive family history with FH (69.6 vs 47.1 %). Women with positive family history smoked more frequently than females with negative family history (51.1 vs 31.1 %). Among patients with negative family history compared with patients with positive family history there were more people who at admission had hyperglycemia exceeding 11.1 mmol / l (10.3 vs 4.4 %). Multiple vessel disease and coronary calcinosis were present in 73.2 and 24.7 %, respectively, of patients with positive family history, and in 56.9 and 9.8 %, respectively, of those with negative family history. Among patients with positive family history multivessel disease was more frequent in the subgroup with FH, while coronary calcinosis was more frequent in the subgroup without FH. CONCLUSION: Thus, premature development of ACS might be associated not only with genetic factors but also with family history ("inheritance") of adverse habits. Herewith coronary calcinosis is more prevalent in patients with FH.