Object: the process of formation of bone regenerate in victims after a diaphyseal fracture and the influence of mechanical and other factors on it. Aim: to increase the efficiency of treatment of patients with diaphyseal fractures of the long bones of the extremities by establishment of regularities of bone regenerate formation and improving the method of functional treatment using external fixation devices and orthoses. Methods: experimental animal modeling; clinical; radiological; ultrasonographic; histological; biomechanical (mathematical finite element modeling); statistical. Scientific knowledge of regularities of osseous regenerate formation after shaft fracture of extremities bones has been supplemented. It has been proven for the first time that fibrin-blood clot formed in the area surrounding the fragments is a primary bioactive mechanical frame, where proliferation and differentiation of cells with further formation of osseous tissue occur. It has been shown that poorly differentiated cells are located on fibrin septa, and their longitudinal axis is located in parallel to fibrin fibers. Formation of fibrin-blood clot has been investigated under іn vitro conditions for the first time, and the effect of mechanical factors (stirring and pressure) on it has been shown. As a result of ultrasonographic examinations, it has been established for the first time that shape and location of osseous regenerate conform to shape and location of fibrin-blood clot. Particulars of stress-strain behavior of fibrin-blood clot and periosteum in the area surrounding the fragments have been studied for the first time based on mathematical calculations using finite-element models. The maximum fibrin stress value was identified near the bone; it was decreased in the central portion of the spindle and increased again when approaching the periosteum. The highest fibrin stress was identified in case of connection of fragments with external fixation device under the conditions of either vertical or transverse loading. When the fragments were connected with a plate or an intramedullary blocked rod, fibrin stress level was at least twice as low. Values of linear displacement of fragments under the conditions of functional therapy of shaft fractures of long bones of extremities with an orthosis or a rod external fixation device were analyzed for the first time. It has been established that displacements of 13–40 % (versus the initial value between the control points), if applied during the first three weeks after fracture, are associated with formation of integral periosteal osseous regenerate in 95–98 % of the cases (depending on fracture location). Based on the identified regularities, staging of formation of osseous regenerate after a shaft fracture has been specified, treatment principles have been formulated, and their procedures have been improved. Based on the results of experimental, clinical, and theoretical studies, procedures of minimally invasive functional treatment of patients with shaft fractures of the bones of extremities using rod external fixation devices have been developed. The procedures combine special, interrelated procedures of coaptation of fragments and their connection with rod external fixation device, procedure of functional load of affected extremity, control of regeneration process in cases of fractures of thigh bone and shoulder bone, shin bones. Their use allowed to decrease the rate of fragments non-union episodes (which require additional surgical therapy) in the above category of victims versus the data of independent multicenter studies, where the methods of immersed (bone or intramedullary) osteosynthesis were initially used during therapy. Thanks to accumulated clinical experience, structures of devices for external fixation of fragments have been improved, their manufacturing technology has been developed, and their production has been implemented. The results of the study were introduced into clinical practice of the KZOZ "Kharkiv Regional Clinical Trauma Hospital", the Military Medical Clinical Center of the Northern Region of the Ministry of Defense of Ukraine, the National Military Medical Clinical Center "The Main Military Clinical Hospital" of the Ministry of Defense of Ukraine, the Clinical Hospital named after Kh. I. Mechnikov, National Children's Hospital "OHMATDYT". Traumatology and Orthopaedics.
