Biomechanical characteristics of fixation methods for floating pubic symphysis

Abstract

BackgroundFloating pubic symphysis (FPS) is a relatively rare injury caused by high-energy mechanisms. There are several fixation methods used to treat FPS, including external fixation, subcutaneous fixation, internal fixation, and percutaneous cannulated screw fixation. To choose the appropriate fixation, it is necessary to study the biomechanical performance of these different methods. The goal of this study was to compare the biomechanical characteristics of six methods by finite element analysis.MethodsA three-dimensional finite element model of FPS was simulated. Six methods were used in the FPS model, including external fixation (Ext), subcutaneous rod fixation (Sub-rod), subcutaneous plate fixation (Sub-plate), superior pectineal plate fixation (Int-sup), infrapectineal plate fixation (Int-ifa), and cannulated screw fixation (Int-scr). Compressive and rotational loads were then applied in all models. Biomechanical characteristics that were recorded and analyzed included construct stiffness, micromotion of the fracture gaps, von Mises stress, and stress distribution.ResultsThe construct stiffness of the anterior pelvic ring was decreased dramatically when FPS occurred. Compressive stiffness was restored by the three internal fixation and Sub-rod methods. Unfortunately, rotational stiffness was not restored satisfactorily by the six methods. For micromotion of the fracture gaps, the displacement was reduced significantly by the Int-sup and Int-ifa methods under compression. The internal fixation methods and Sub-plate method performed well under rotation. The maximum von Mises stress of the implants was not large. For the plate-screw system, the maximum von Mises stress occurred over the region of the fracture and plate-screw joints. The maximum von Mises stress appeared on the rod-screw and screw-bone interfaces for the rod-screw system.ConclusionsThe present study showed the biomechanical advantages of internal fixation methods for FPS from a finite element view. Superior stabilization of the anterior pelvic ring and fracture gaps was obtained by internal fixation. Subcutaneous fixation had satisfactory outcomes as well. Sub-rod fixation offered good anti-compression, while the Sub-plate fixation provided favorable anti-rotational capacity.

Modified pedicle screw-rod versus anterior subcutaneous internal pelvic fixation for unstable anterior pelvic ring fracture: a retrospective study and finite element analysis

“…The FEA results of the present study show that the displacement distribution and vM stress were similar in the MPSRF and INFIX models compared to the intact model, indicating that both fixation techniques can effectively treat anterior pelvic ring fractures. Song et al reported that the maximum von Mises stress appeared at the rod-screw and screw-bone interfaces in floating public symphysis by finite element analysis, which is basically consistent with our result analysis [22]. However, the maximum displacements of the pelvis and implant were lower in the modified group than in the conventional group in the single-(left/right) and dualleg standing and sitting postures, indicating greater stability.…”

Modified less invasive anterior subcutaneous fixator for unstable Tile-C-pelvic ring fractures: a biomechanical study

“…The INFIX also seems more effective than external fixation at reducing postoperative surgical site pain [16]. Other disadvantages of the external pelvic fixator include worse outcomes in diabetic and obese patients [17].…”

“…The symphysis-fixed INFIX (extended unilateral INFIX) could provide improved rotational stability compared to the bilateral INFIX with fixation of the symphysis. A finite element study by Song et al [17] showed better rotational stability of the plate fixation fixed to the symphysis compared to the bilateral INFIX. It was concluded that this could be due to the fixation to the symphysis [17].…”

“…A finite element study by Song et al [17] showed better rotational stability of the plate fixation fixed to the symphysis compared to the bilateral INFIX. It was concluded that this could be due to the fixation to the symphysis [17].…”

Evaluation of strategies for the treatment of type B and C pelvic fractures

“…This study has several limitations. The nature of a registry analysis does not allow us to consider rather rare fracture configurations such as a floating pubic symphysis, which in some cases certainly requires internal fixation 24 . Some patient characteristics such as socioeconomic status or behavioural characteristics were not captured in the registry and might potentially bias the results.…”