مقايسه دو روش تثبيت براي درمان شكستگي ديستال استخوان بازو در بيماران دچار پوكي‌استخوان: تحليل اجزاي محدود

Considering the anatomy of the arm an‎d its level of function, the elbow is one of the most important joints of the upper limb. Fracture of this joint causes pain an‎d impaired movement of the upper limb; therefore, the treatment of distal humerus fractures is essential. Distal humerus fractures are among the most common fractures in people with osteoporosis. One of the distal humerus fractures according to the OA classification is the A2 extra-articular fracture. This study aims to investigate two different fixation models for A2 extra-articular distal humerus fractures. Fixation with two perpendicular plates is a common method for treating this fracture type. In the present study, the biomechanical performance of fixation using orthopedic screws placed crosswise in the bone is investigated an‎d compared with the conventional screw an‎d plate fixation method.In a 3D finite element model, CT images of the humerus of a person with osteoporosis were used. In this model, a 1 mm fracture was created according to the A2 extra-articular fracture, an‎d the simulation of fixation using screws an‎d plates an‎d cross screws under compression, tension, bending, an‎d lateral loading was performed using the finite element method. The maximum bone stress in flexural an‎d lateral tensile loading in fixation using screws an‎d plates was significantly reduced compared to cross screws. The maximum stress of screws an‎d plates an‎d cross screws in compression an‎d tension loading was almost the same an‎d was about 150 MPa, an‎d in bending an‎d lateral loading, fixation with screws an‎d plates created a stress equivalent to 45.9 MPa an‎d 31.9MPa, respectively, which was much lower than the maximum stress of cross screws. According to the results obtained an‎d the lower stress an‎d as a result of the weakening of the bone in the area of screw placement, the ability of the bone to retain the screw is reduced, an‎d the possibility of screw loosening increases. Cortical screw loosening near the fracture area is more likely than in other areas for the aforementioned reason, an‎d the probability of this loosening was reported to be lower in the screw-an‎d-plate fixation method than in the cross-screw fixation method. Also, the more the direction of force application is in relation to the direction of screw placement, the greater the screw pull-out force. Therefore, it is expected that in axial loading (compression an‎d tension) the screw-an‎d-plate model will require a greater pull-out force than in the cross-screw fixation model. In bending loading, given that the load direction is perpendicular to the screws in both fixation models, it is expected that approximately the same force will be required to pull out the screws in both fixation models; however, in lateral loading, given that the angle of force application is aligned with the direction of screw inser‎tion, it is expected that a lower pull-out force will be required than in the cross-screw fixation model.

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