Validation of the Angle Bisector Method for Precise Tibiofibular Syndesmosis Fixation Angle Using Computed Tomography and 3D-Printed Models
Authors: Karaismailoglu Bedri , Yerlikaya Davut , Özdemir Ceren , Dalbudak Kubra , Komurcu Tolga Barkan , Yolcu Musa Batuhan , Celayir Arin , Sahin Erdem , Tutuncu Mehmed Nuri , Kara Mustafa 
Published: December 2023

Category: Ankle; Trauma Introduction/Purpose: The proposed ideal alignment for the syndesmosis involves a line connecting the centroids of the fibula and tibia, but there is uncertainty about the optimal intraoperative method for determining the appropriate fixation angle. This is due to the fact that the AO guidelines do not account for patient or level-specific factors, and the determination of the angle relative to the coronal plane relies on the surgeon's judgment. Inexperienced trauma surgeons may encounter significant problems with syndesmotic malalignment as a result. The goal of this study was to validate the effectiveness of the angle bisector method using computed tomography and 3D-printed ankle models, in order to determine whether it can assist in achieving proper screw trajectory for syndesmotic fixation. Methods: The angle bisector method was utilized to identify a precise trajectory for the true syndesmotic axis, using the bisector of the angle formed by two lines tangential to the anterior and posterior fibula and tibia. CT validation was made on CT angiography of 50 consecutive patients. DICOM data from 16 ankles were used to create 3D anatomical models which were printed using a desktop FDM printer. Two trauma surgeons performed syndesmotic fixations using the angle bisector method at 2 cm and 3.5 cm proximal to the joint space, after identifying the bisector of the angle formed by two K-wires tangential to the anterior and posterior fibula and tibia. The axial sections of CTs and printed 3D-models were analyzed using software to determine the relationship between centroidal axis and the inserted screws. The measurements were made twice by two blinded observers, with a two-week interval. Results: The results of the study show that the angle bisector method provides a reliable direction with minimal differences at both the 2 cm and 3.5 cm levels. The average angle between the centroidal axis and screw trajectory was 2.4° ± 2° at the 2 cm level and 1.3° ± 1.5° at the 3.5 cm level. Furthermore, the average distance between the fibular entry points of the centroidal axis and screw trajectory was less than 1 mm at both levels, indicating that the angle bisector method can serve as an excellent entry point for syndesmotic fixation on the fibula. The inter- and intra-surgeon analyses showed excellent consistency, with all ICC values above 0.90. Similarly, inter- and intra-observer consistencies regarding the measurements were also excellent. Conclusion: The study demonstrated that the angle bisector method was successful in identifying the original syndesmotic axis and aided in the precise placement of implants in the desired direction. The method has the potential to be replicated intraoperatively and could serve as a basis for the development of a novel surgical guide for determining the correct syndesmotic axis. However, safety analysis using cadavers should be conducted prior to clinical implementation.