The purpose of this work was to create optimal tactics for surgical treatment of complicated and chronic tears of the rotator cuff of the shoulder. In order to substantiate the choice of tactics and prove the importance of stabilizing the shoulder joint, a semi-natural biomechanical modeling of the structures of the shoulder joint and vascular-nerve bundle was created and carried out, as well as clinical, biophysical, instrumental studies and a comparison of the results obtained in the treatment of the main group of patients with a retrospective analysis. To determine the behavior of the structures of the shoulder joint in case of damage to the m.supraspinatus or n.axillaris or plexus brachialis, a semi-natural biomechanical simulation of the shoulder joint was carried out. In this method, we analyzed the behavior of the structures of the vascular-nerve bundle of the shoulder joint as a result of traction displacement of the head downwards by 25 %, 50 % and 100 % of its diameter. On the basis of axial CT scans of the intact shoulder joint obtained on the Toshiba Activion 16 computer tomograph, the spatial geometry of the shoulder joint structures was reproduced using the Mimics software package in automatic and semi automatic modes. A simulated 3-D model of the shoulder joint was created using the SolidWorks software package. Soft tissue elements - m.deltoieus and m.supraspinatus muscles, vessels and nerves, morphometric and topographical data about which were obtained from cadaver material, were added to the model. The location and ratio of model elements are as close as possible to real conditions. The existing deviations did not introduce fundamental disagreements and did not affect the results of the calculations. Further calculations were carried out by the SE method, which allows to study the evolution of the deformation process under the load of the elements of the shoulder simulation model, namely, bone tissue, muscles and nerves, with large geometric and physically nonlinear properties of materials and time-varying external influences. In order to calculate VAT using the SE method, simulation models were imported into the "ANSYS" program. Averaged physical properties of biological tissues obtained from literary sources were used in the calculations. For comparative analysis, the smallest value of the limit of tissue strength was chosen. In a semi-automatic mode, 3 variants of the SE model were generated with a distal displacement of the head of the humerus by 25 %, 50 % and 100 % of its diameter, under the influence of the mass of the upper limb, which simulates the exclusion of the function of the deltoid muscle. The models had an average of 393,000 nodes and 128,000 elements. To increase the accuracy of calculations, the mesh is compacted in the areas of contact and for nerve elements. The CE grid is mainly represented by tetrahedral elements (Tetrahedrons), the size of which on the main model does not exceed 2 mm, in places of thickening 0.1 - 1 mm. As the load of the model, the effect of the calculated mass of the upper limb for an average person weighing 75 kg in a standing position, taking into account the mass inertial characteristics: shoulder - 2.7 %, forearm - 1.6 %, hand - 0.6 %, in total - 4.9 % of the total weight of the human body. Therefore, a force of 750N x 0.049 = 36.75N was applied to the distal end of the humerus of the model. The results showed that the distal movement of the humeral head of the model by 25-100 % of its diameter is accompanied by joint movements of the structures of the vascular-nerve plexus. However, all elements of the plexus do not move evenly due to their anatomical location, inter-tissue connection and their own mechanical properties. At the same time, n. musculocutaneus, fasciculus posterior plexus brachialis and n. ulnaris have the largest values according to indicators of total displacement (Total Deformation) - up to 52.9 mm, 44.4 mm and 41.4 mm, respectively. Large displacement indicators are accompanied by a natural increase in stress and strain values on individual structures of the neurovascular plexus of the model. Thus, according to stress indicators, n.radialis and a.axillaris were most affected, their values progressively increased with the increase in the distal displacement of the head of the humerus up to 100% of its diameter and exceeded the limits of tissue strength. Combined data of stress indicators on model elements for different variants of distal displacement of the humeral head (25, 50 and 100% of the diameter). According to deformation indicators, n.radialis and n.axillaris were most affected. Exceeding the strength limits by 2.5 times, the values of deformations for n.radialis, already at a distal displacement of the humeral head of the model by 25%, progressively increased with an increase in the distal displacement of the humeral head up to 100%, reaching values that exceed the limits by 9 times strength of nervous tissue.
