Russian Journal of Biomechanics

Surgical treatment of overload metatarsalgia is the actual problem, as this disease is subject to a large number of older patients. This contributes to the polyetiology of the disease. This article provides a comparative analysis of different types of surgical treatment of this pathology. The efficiency of surgical technique, which was supplemented by reinserting plantar ligaments of the metatarsophalangeal joint to the place of separation from the proximal phalanx of the finger compared to a classic small osteotomy of the metatarsal bones and phalanges. With the aim of evidence of the effectiveness of the proposed methods of treatment was used the method of podobarometry, which showed its effectiveness.

The aim of the study was biomechanical modeling of the development and influence of thoracic aortic aneurysm on the hemodynamics of the vessel. Aortic aneurysm is an irreversible expansion of the aorta and is one of the diseases of the cardiovascular system with a high fatal outcome. Biomechanical modeling included: setting the task, building a virtual model of the object under study, setting boundary and initial conditions and properties of materials, also assessment the results of a numerical experiment based on the physiological characteristics of the object. Two three-dimensional virtual models of the thoracic aorta were constructed on the basis of computed tomographic angiography of a real patient: with an aneurysm of the ascending division and after prosthetics. To analyze the development of pathology, were created additional virtual models with different degrees of aneurismal expansion. The calculation is carried out taking into account the parameters characterizing the work of the cardiovascular system (blood pressure value, dynamic viscosity and blood density). The analysis of the results showed a change in the character of blood flow, the formation of region of blood stagnation in the aneurysm zone. It was revealed that with the increase in the geometric dimensions of the pathology there is a drop in the blood flow rate and an increase in the flow pressure values in the aneurysm. Asymmetric distribution of pressure values on the inner surface of the aorta, triggered by the displacement of the flow velocity vector relative to the axis of the blood vessel, can to incite further development of an aneurysm.

This paper presents the results of biomechanical modelling of the “femur-implant” system under condition of non-standard cone size and addition of the developed hip replacement adapter. One of the most effective treatment methods for diseases and injuries of the hip joint is total hip replacement. Expansion of indications for total hip replacement led not only to an increase in the percentage of implants, but also to an increase in the number of recorded complications. The leading position among complications is occupied by aseptic instability of the endoprosthesis components. With isolated reimplantation of the endoprosthesis cup and the friction pair “head-liner”, orthopedists are faced with the problem of non-standard sizes of the neck cone of the stem. This leads to the need for extraction of stable femoral components and a significant decrease in the effectiveness of the technique. To solve this problem, we developed an adapter, which is shaped as a truncated cone. The inner diameter of the adapter corresponds to the outer diameter of the non-standard cone, and the outer diameter of the structure has standard size. Biomechanical modelling methods were used to introduce this development into practical medicine. This paper presents stages of creating biomechanical models of the "bone-implant" system. Biomechanical modelling is carried out in the Ansys Workbench software. The main attention is focused on the distribution of equivalent stress values. Stresses occur in the metal structure elements with application of physiological loads. The maximum values of equivalent stresses in the structure under study at the load of 800 N (133.3 MPa) are comparable to maximum equivalent stresses in standard endoprosthesis structures, ranging from 31 to 195 MPa. The maximum values do not exceed yield strength of the material, which is 350 MPa. Thus, the results of biomechanical modelling showed high operational reliability of the developed adapter with a non-standard size of the femoral component’s neck.

Neurological gait disturbances require long-term gait rehabilitation. According to existing research results, robot-assisted gait training devices are designed to improve patient’s walking capabilities and to eliminate the operator's physical overloading. The aim of this paper is to present an ergonomic analysis of commercially available robot-assisted gait training devices, including both the operators and patients postures during robot-assisted gait training therapy. This ergonomics analysis was performed on the Hocoma’s Lokomat Pro, involving five randomly chosen device's operators and ten adult and children patients who received gait therapies on the day of the experiment. Both evaluators concluded that the most problematic points, from aspects of safety and fatigue for the operators, were the preparation process of the device, device adjustments to each patient individually, and the noise produced by the device. Subsquently patients mostly struggled with the device's ramp and uncomfortable harness. It was noted that although the Lokomat Pro is the most widely used robot-assisted gait training device with many advantages that contribute to improved patient ́s gait capacities, like in every medical device, there is always room for improvement. Research and development of robot-assisted gait training devices is a long-term process requiring multidisciplinary cooperation. The cooperation represents an enriching experience for a whole team of specialists and ensures that the product meets the criteria for the end-users.

Research of resistive vessels, assessment of their functional state is one of the key issues of blood circulation from the point of view of physics, angiology, rheology, blood biomechanics and related sciences. The article examined some physical quantities that describe the functional state of resistive arteries. According to the results of our study, such physical components as the thickness of the intimal medial layer, the coefficient of resistance of the resistive arteries and Young's module turned out to be interesting pathophysiological markers that can reflect the change in the vascular wall at earliest stages, when there are no yet other precursors of the disease. It is very important to continue research in this direction in order to deepen, transport and generalize our data to large-scale cohort studies.

This study is devoted to assessing the fatigue strength of a self-expanding Nitinol frame for a prosthetic heart valve when reconstructing the conditions of primary implantation in the mitral position. The object of research is a stent-like supporting frame, which is a cellular structure that performs the function of the main fastening and maintaining the shape of the leaflets and cover. The study included two stages of the formation of the stress-strain state of the frame: the creation of a mathematical model that provides an assessment of the state of the structure of the support frame in the final state and an assessment of the fatigue strength. It is shown that during the packaging of the frame in the delivery system (compression), a high degree of localization of inelastic deformations leading to surface destruction of a number of cells and joints at the final stage of the compression process, is noted. In a number of cell vertices and frame junctions, the fatigue strength coefficient exceeded its limit value, which indicates their destruction under the influence of long cyclic alternating loads. The main effect on the fatigue strength of the structure is the stress-strain state obtained at the stages of compression and implantation. To meet the conditions of static and fatigue strength, a modification of the support frame structure is required.

The numerical finite element method is proposed as a method to model the erythrocyte aggregation process. The results of the simulation of an experiment are presented in which hydraulic micropipettes were used to form a pair of erythrocyte aggregates in a dextran medium with a molecular mass of 150 kDa. The parameters of erythrocyte aggregation were determined: the value of pressure normal to the surface of erythrocytes, which attracts them; size of the contact zone; erythrocyte membrane strain energy; by comparing the results obtained experimentally and performed numerical simulation. The mathematical modeling of the erythrocyte aggregation process was performed taking into account shear stresses. The shear stress values were obtained using the Couette model and compared with the results of experiments on the separation of paired aggregates of erythrocytes.