Tamás Bodzay1, Tamás Burján2, Cecília Bagdi2, István Flóris1, Zsolt Vendégh1, Károly Váradi2

1National Institute of Traumatology and Emergency Medicine, Budapest, Hungary
2Budapest University of Technology and Economics, Faculty of Mechanical Engineering, Institute of Machine Design, Budapest, Hungary

Keywords: Finite element analysis; models, structural; pelvic bones/ injuries/physiology; sacrum/injuries; stress, mechanical.


Objectives: We developed a finite element model to compare the stabilization methods for the treatment of vertically and rotationally unstable type C pelvic ring injuries. Materials and methods: Using the COSMOS/M DesignSTAR system, finite element modeling was performed to simulate a type C pelvic ring injury (Denis type 1 fracture of the sacrum and symphysiolysis). The latter was treated with a 4-hole reconstruction plate; the sacrum fracture was fixed with two 2-hole reconstruction plates on the ventral surface or a dorsally applied narrow trans-sacral DC-plate. Finite element modeling included not only the bones and joints, but also mechanically important ligaments. We measured maximum stress in the bones and the ligaments, distribution of stress, displacement and shift. The results were compared with those obtained from measurements performed on cadaver pelvis models.
Results: After direct plating, maximum stress was 21.46 MPa in the plates, and 7.93 MPa in the bones when loading on two feet. These values were 31.1 MPa and 29.1 MPa, respectively when loading on the injured side. With trans-sacral plating, the corresponding figures were 57.36 MPa and 14.14 MPa on two feet, and 223.5 MPa and 23.52 MPa on the injured side. Maximum displacement and shift measured at the two facets of the fracture gap after direct plating were 0.45 mm and 0.01 mm on both feet, and 1.71 mm and 0.28 mm on one foot, respectively. The corresponding figures for trans-sacral plating were 1.099 mm and 0.71 mm on both feet, and 3.55 mm and 2 mm on the injured side. The results of finite element modeling were in agreement with those obtained from bony-ligamentous cadaver pelvis specimens.
Conclusion: Finite element modeling may be useful for the comparison of stabilization methods used for the treatment of pelvic ring injuries.