The biomechanics of various fixations for syndesmotic joint diasthesis: a finite element study

Introduction Management of syndesmotic injury is very much open to debate. Controversies aroused in many aspects, and yet no single treatment is considered as gold standard. The surgical management is still evolving. Positional screw has been widely used as a stabilizer while waiting for healing but the utilization of screw itself is varied. Kirschner wire has been used for temporary stabilizer and the clinical results revealed good outcome. Interosseous suture has emerged as an alternative way in restoring syndesmotic joint function, also with good clinical outcome. We conduct a study to analyse the behaviour of all three implants used in the management of ankle syndesmosis diasthesis. Method Three finite element models, consist of distal half of tibia and fibula with talar bone were developed. The models were completed with sets of ligaments, including interosseous membrane, all syndesmotic ligaments, deep portion of deltoid ligament and lateral collateral ligaments. Verifications were done using three tests, which are axial loading, lateral separation of fibula and anterior drawer test of the talus. Once all ligaments has been verified, syndesmotic ligaments were removed and exchanged with implants. 600N axial loading was applied and the behaviour of syndesmotic movement recorded. Result Models with positional screw and two parallel Kirschner wire recorded very minimal syndesmotic joint movement, which are 0.03mm and 0.04mm respectively, after given 600N axial load. The model with interosseous suture recorded 2.1mm fibula movement in relation to tibia after given 180N axial load, and further 4.4mm after 600N axial load applied. Conclusion 3.5mm positional screw and two parallel Kirschner wire will result in stable but rigid fixation to the syndesmotic joint with axial loading. Interosseous suture will allow normal physiological movement of syndesmotic joint up to 180N before diasthesis occur.