Mathematical analysis of the mechanics and rigidity of fixation of transverse acetabular pelvic fractures using a finite element model of the "external fixation apparatus — pelvis system"

The finite element model was used to study the mechanics of the deformed state of the system "external fixation apparatus — pelvis" in pelvic bone fracture. It was found that in transverse acetabular fractures of the B1.2/3 type (according to the AO/ASIF classification) with bilateral damage to the posterior pelvic semicircle by changing the elastic modulus of the iliac-sacral articulation in the experiment on the finite element model "pelvis" without stabilising it with an external fixation apparatus, the displacement of bone fragments in the control zone between points 739-740 is in direct dependence on the state of the iliac-sacral articulation. Thus, at the elasticity modulus of the bone fragments 20000 MPa there is their high stability, and the decrease in the elasticity modulus entails an increase in the displacement of the bone fragments in the control points with a pronounced displacement along the vertical Y axis up to 106.0 mm, which determines the complete displacement of the bone fragments by 114.0 mm. The external fixation apparatus provides sufficient stability of the bone fragments for verticalisation of patients when the elastic modulus decreases to 200 MPa in bilateral injuries, which corresponds to damage to the anterior or posterior iliosacral ligament. Further reduction of the elastic modulus in the projection of the iliosacral joint requires additional methods of fixation of the iliosacral joint. In unilateral iliosacral joint injuries, stabilization of horizontal pelvic acetabular fractures with external fixation apparatus provides high stability of bone fragments that do not require additional fixation methods.