Abstract
Comminuted fractures of the humerus are generally treated with the intramedullary rod fixed by screws or locking plate system, and clinical results are satisfactory. We also know very well that the success of this agriculture depends on the stability and adaptability and integration of the bone tissue of the humerus with this nail in the long term, with less and optimal distribution of stress in the surrounding bone. For this reason, we began to think and look for rational solutions to reduce and minimize this stress which has become an important issue in this area. In this regard, we have proposed a new model of hollow nail made of titanium proposed by some scientific specialists in this field of biomechanics, and we inserted from the proximal humeral head, and to ensure the stability of the nail inside the bone and prevent slippage, we attached small screws. To know the extent of the realization of these nails under the influence of the forces applied to them, finite elements in three dimensions as well as the program ANSYS Workbench 16.2 were used. Two intramedullary rods were instrumented in the finite element model of a medial humeral fracture. Axial, shear, and rotational loads were applied to the models under normal and osteoporotic bone conditions. The whole simulation was repeated 5 times for each fixator. To evaluate the biomechanical characteristics, the distribution of von Mises stresses and strains, total displacement in the nail, cortical and cancellous bone were compared. The numerical results showed that the intramedullary rod system with 4 screws and 6 screws played a very important role in the absorption and thus minimization of stresses. On the other hand, the nailing system fixed with screws was too great a role in reducing the stress compared to intact model. In general, the new model nailing system secured with screws gave a lower level of von Mises stress and strain at the cortical and cancellous bone of the humerus compared to the intact model. The results provided a theoretical basis for the selection of an appropriate surgical model.
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