Biomechanics comparison between endobutton fixation and syndesmotic screw fixation for syndesmotic injury ankle fracture; a finite element analysis and cadaveric validation study.

INTRODUCTION

Various syndesmotic fixation methods in ankle injury are recommended; however, a lack of biomechanical information persists regarding the stiffness of the fixation methods. The current study thus aimed to assess biomechanical cadaveric validation and perform a finite element analysis of syndesmotic fixation comparing endobutton vs. screw after syndesmotic injury with an ankle fracture.

METHOD: Five pairs of ankles of fresh cadavers were used for the validity test for Anterior Inferior Tibiofibular Ligament (AITFL), Posterior Inferior Tibiofibular Ligament (PITFL), and Interosseous ligament biomechanics properties. Four finite element models (FEM) were created: an intact model, a fracture model with/without syndesmotic injury, an endobutton fixation model, and a syndesmotic screw fixation model. Each FEM was tested vis-à-vis external rotation force, anteroposterior translation force, and compression force until model failure. The primary outcomes were stiffness and force until failure.

RESULT: The respective anteroposterior translation force for the stiffness of the intact model, the screw fixation model, and the endobutton fixation was 8.14, 9.15, and 8.17 N/mm. The respective external rotation force for the stiffness of intact, screw fixation, and endobutton model was 0.927,0.949, and 0.940 Nm/degree. The respective stress under compression force in the intact, screw fixation, and endobutton model was 39.94,25.59, and 37.30 MPa.

CONCLUSION

Both screw and endobutton fixation models provided more translation, compression, and rotation stability than normal syndesmosis, but the screw model provided greater translation and compression force stability than the endobutton model. There was no difference in rotational stability between the two models. We thus recommend the same rehabilitation protocol for both fixation methods; however, vigorous translation and compression should be avoided when using endobutton fixation.