Osteosynthesis of the pubic symphysis: development of a finite element model of the pelvis to compare different fixation techniques

Pelvic injuries are characterized by the fracture of one or more pelvic bones and can be classified using multiple systems. In particular, symphysis fractures categorized as rotationally unstable and vertically stable are classified as B1 fractures according to the Tile classification, and APC I and II according to the Young and Burgess classification. Open reduction and osteosynthesis, achieved through plate fixation of the pelvic ring, are the main techniques used in this case. In literature, various plate designs are documented, such as two-hole, multi-hole, and double plates. However, these methods may lead to implant loosening due to the excessive rigidity imposed on the pelvic ring. The ideal scenario should involve a material capable of replicating the flexibility of the ligaments. In response to this issue, semi-rigid implants, such as the Endobutton CL, have been introduced to enhance these characteristics. This particular fixation method is commonly used in anterior cruciate ligament reconstructions, as it can replicate ligaments’ behavior and joint flexibility while supporting physiological healing. This thesis work aimed to develop and validate a finite element (FE) model to compare traditional plate fixation with the Endobutton CL technique. A 3D mesh of the pelvis was created using the Altair HyperMesh software to recreate the experimental assets involving artificial SawBones pelvis specimens employed within experimental tests. A total of three different FE models were created: a fractured model, where the symphysis was removed; a model fixated with a plate; a model fixated with the Endobutton, mirroring the experimental tests. The simulations were conducted using a linear static analysis in Abaqus. A vertical displacement of 7 mm was applied to the sacrum, while proximal femur-like elements articulated with the pelvis through the acetabulum in accordance with the experiments. The symphysis opening was computed and compared with experimental data, while the inferior part of the bone was connected to the two base supports, constraining the vertical displacement. Experimental and numerical results were compared in terms of the symphysis opening, computed by following the displacements of markers glued to the specimens and of their corresponding nodes in the FE models. A good agreement between experimental and numerical symphysis opening could be observed, with the higher degree of mobility of the Endobutton fixation compared to plate fixation highlighted.