Object: complications from the implant after replacement of post-resection tumor defects of the proximal humerus by a modular endoprosthesis. Purpose: to improve the results of modular endoprosthetics of patients with tumors of the proximal humerus by developing and improving a combined fixation system of endoprosthesis. Methods: clinical, radiological, computed tomography, magnetic resonance imaging, patent information study, pathomorphological, mathematical modeling using finite element methods, animal experiment, biomechanical study of experimental preparations, statistical. For the first time, the effectiveness of the combined fixation of the endoprosthesis to the bone has been proved by studying the mathematical models of the "endoprosthesis – humerus" system in conditions of three levels of resection (upper third, upper half and segment at the border of the middle and lower third of the humerus), using additional extracorporeal fixation and without her. For the first time in the experiment it was proved that the border of the upper and lower halves of the humerus is the most unfavorable level of resection, since the greatest load occurs in the "critical zone" – at the site of the endoprosthesis body transition into the intramedullary stem. As a result of the study of the stress-strain state of the "endoprosthesis – humerus" system it was found that the maximum stresses in models with endoprostheses without additional extracorporeal fixation system are distributed along the surface of the bone canal, in the endoprosthesis fixation zone in the bone ("critical zone") and along the entire length intramedullary stem. In the case of using an endoprosthesis with a combined fixation system, the stress in these areas was found on average 4.5 times lower. For the first time in experimental animals bone defects were modeled and replaced by modular endoprostheses with intramedullary and extracortical fixation. The effectiveness of the use of the endoprosthesis with a combined fixation was proven. The improved modular endoprosthesis system (patent No. 83345, Ukraine) allows replacing osteoarticular defects of the proximal humerus of considerable size after removal of the tumors, retaining the function of the shoulder joint with preservation of the muscular and nervous structures, shortening the period of immobilization of the limb and in the early restoration of its function. The use of modular endoprostheses with intramedullary fixation in combination with extrakortical allowed to obtain a strong connection with the bone and eliminate complications from the implant (aseptic instability, endoprosthesis fracture, periprosthetic fracture) in the early and late postoperative period. The introduction of experimental data for the first time proved the clinical effectiveness of the developed modular endoprosthesis of the proximal humerus with a combined fixation system. The results of the research were introduced into clinical practice of SI "Sytenko Institute of Spine and Joint Pathology National Academy of Medical Sciences of Ukraine", Public Health Institutions "Kharkiv Regional Clinical Traumatology Hospital", Public Health institutions "Regional Clinical Hospital - Center for Emergency Medical Care and Catastrophe Medicine ", public health Institutions "Kharkiv City Multiprofile Hospital No. 18", Public Health Institutions "Rivne Regional Clinical Hospital" of Rivne Regional Council, Regional Center of Orthopedics, Traumatology and Vertebrology, as well as in the educational process of the Department of Traumatology and Orthopaedics of Kharkiv National Medical University, Ministry of Health of Ukraine. Traumatology and Orthopaedics.
