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The treatment of patients with tibial fractures and overweight has certain peculiarities due to the increased load on the osteosynthesis device. Objective. To compare the stress-strain state of models of the lower leg with a fracture of the tibia in the upper third of the diaphysis under the influence of torsional load under different options of osteosynthesis depending on the patient's weight. Methods. Using the finite element method, a fracture in the upper third of the tibia and three types of osteosynthesis were modeled: using an external fixation device (EFD), a bone plate, and an intramedullary rod. A torque of 7 Nm and 12 Nm was applied to the tibial plateau. The results. The highest indicators of the stress level in the fracture zone (6.3‒10.8 MPa) and on the metal structure (251.0‒430.2 MPa) were determined in the model with a bony plate. In the model with osteosynthesis with the help of EFD, a fairly low stress level (0.2‒0.3 MPa) was established in the fracture zone, but a high one in the proximal part of the tibia (6.7‒11.5 MPa). The lowest values of stresses in the fracture zone (0.1‒0.2 MPa) and the proximal fragment of the tibia (0.6‒1.0 MPa) were determined under the conditions of reproduction of osteosynthesis using an intramedullary rod, but in the distal part of the tibia the stresses remained quite high — 11.1‒19.0 MPa. Conclusions. The values of stresses in the fracture zone in the models with EFD and intramedullary rod were significantly lower than the values of the intact bone, with the periosteal plate - only at a load of 7 Nm. In the distal fragment of the tibia, the highest stress level was determined in the model with osteosynthesis with an intramedullary rod, in the proximal one — with EFD. Among the metal structures, the greatest stresses were found in the periosteal plate and around the fixing screws and rods under the conditions of its use. The function of the dependence of the amount of stress on the weight of the patient in the elements of the model turned out to be linear and directly proportional.

Recently, there has been a trend towards high statistical indicators of the number of bone fractures of the lower limbs(47.3%), of which diaphyseal fractures of the lower leg bones make up 45‒56 %. Objective. Conduct a comparative analysisof the stress-strain state of leg models with a fracture of the tibia under the torsional loading combined with various optionsof osteosynthesis and depending on the patient's weight. Methods. A fracture was modeled in the middle third of the diaphysisof the tibia and three types of osteosynthesis — with the help of an external apparatus fixation (EAF), periosteal plate andintramedullary rod Bones were attached to the tibial plateau torque of 7 Nm and 12 Nm. Results. It was determined thatthe changes in stress levels in bone tissue depend linearly on the patient's weight. Under simulation conditions stabilizationof the fracture with the help of EAF and intramedullary stress rod in the fracture area were found significantly lowerthan the level of indicators of intact bone. In this same zone in the model with a bony plate, the value stress levels were lowerthan the intact model bone, but with an increase in the patient's weight to 120 kg, these indicators almost leveled off. The highest stress level was recorded in the distal part of the tibia in the model with intramedullary rod osteosynthesis, and inthe proximal one, the stresses that exceeded the parameters of the model with intact bone were determined under the conditions use of EAF. The largest in metal structures stress is detected in the periosteal plate. Conclusions. The highest stresses in the fracture zone (5.8‒9.9 MPa) and on the metal structure (360.0‒617.0 MPa) was recorded in a model with a bone plate. In the model with EAF in the zone of the fracture, the stresses were at the level of 0.1‒0.2 MPa, in the proximal part of the tibia — 6.3‒10.8 MPa, in the model with an intramedullary rod — 0.1‒0.2 MPa and 0.5‒0.9 MPa, respectively. In the distal partof the stress in the last model remained high — 11.7‒20.1 MPa.