MODELING OF BONE FRAGMENTS FIXATION WITH AN EXTERNAL FIXATION DEVICE FOR BILATERAL ROTATION UNSTABLE PELVIC INJURIES B TYPE ACCORDING TO AO/ASIF CLASSIFICATION

Objective: to determine the stability of bone fragments fixation with an external fixation device in the simulation of bilateral partly unstable pelvic injuries of B type according to AO/ASIF classification and to identify the role of different fixation elements in the stability of fixation. Material and methods: the study was performed on the finite element model of a system “an external fixation device - pelvis” developed for a software package MSCNastran. Formation of a fracture of pubic and ischial pelvic bones was accomplished by means of rupture in the finite element network and decrease of elasticity modulus in the ilio-sacral joint on both sides up to 35 mm at the site of a fracture. Loads were carried on top of the body of the first sacral vertebra with a force of 500H.The second area of application of the load was from the bottom-up on the acetabular roof with a force of 250H. In this study the effect of different elements of an external fixation device on the stiffness of bone fragments fixation was evaluated. Symmetrical elements were removed both separately and together. As a result, the stiffness of a system decreased and the displacement at the fracture site increased. Conclusion: in a model of partly stable pelvic injuries accompanied by general rotation instability in the horizontal and sagittal planes to 35 mm, an external fixation device provided high stability of bone fragments (to 3 mm) due to introduction of bone rods in the iliac wings with the obligatory introduction of the rod in the vertical branches of pubic bones and strengthening the anterior lower bar between the subsystems. What is more, installing the anterior upper bar or introduction of bone rods in the bodies of iliac bone are not necessary.