Comparison of stability in the operative treatment of pelvic injuries in a finite element model

Purpose of the study The comparison of the stability of four surgical methods for the treatment of vertically and rotationally unstable type C pelvic ring injuries. Methods We produced a type C pelvic ring injury (type Denis II fracture of the sacrum and symphysiolysis) on a finite element model, in the case of standing on both feet. We stabilized the symphysiolysis with a five-hole reconstruction plate; the sacrum fracture was fixed in the first experiment with two, two-hole reconstruction plates on the ventral surface, in the second one we applied dorsally the transsacral, narrow DC plate, in the third one with KFI-H plate, and in the last one with iliosacral screw. Finite element modeling was performed by the use of the ALGOR software. Not only bones and joints, but joints and mechanically important ligaments were modeled as well. We measured the shift between the two surfaces of the fracture gap, compared to the results of measurements accomplished on cadaver models. Results Larger shift could be elicited after transsacral plating than after direct plating. These results correspond to those of the parallel investigation of the bony ligamentous cadaver pelvis specimens. The shift values after KFI-H plating and iliosacral screw fixation are larger than after direct plating, but smaller than after transsacral plating. The tension created in the implants is less than the allowed values; therefore, the choice of operation should depend on the type of injury. Conclusions The finite element model may be utilized for the comparison of different methods of osteosynthesis for the treatment of injuries described above. Due to several difficulties in investigations performed on cadaver specimens, this model has undoubted utility.