Research on Determining Bony Landmarks for Accurate Tibiofibular Syndesmotic Fixation: Cadaveric Validity and Safety Analysis of Angle Bisector Method

Category: Trauma; Ankle Introduction/Purpose: Syndesmosis fixation, a common procedure, is vital for restoring ankle biomechanics, but malreduction occurs in up to 52% of cases, necessitating precise anatomic reduction. While AO guidelines recommend a 20-30 degree trajectory in the coronal plane, the proposed ideal syndesmotic alignment is the line connecting fibula and tibia centroids. Intraoperatively determining the ideal fixation angle is challenging due to non-patient-specific and surgeon-dependent angular direction decisions. This study explores the angle bisector method's potential in establishing a patient- and level-specific syndesmotic fixation angle in cadavers, aiming for reproducibility independent of the surgeon. Additionally, the research assesses the safety of this method concerning major neurovascular structures for potential surgical application. By addressing these aspects, the study contributes to enhancing the precision and reliability of syndesmotic fixation procedures. Methods: Fixations on cadaveric leg specimens were conducted utilizing the angle bisector method at two levels (2 cm and 3.5 cm proximal) parallel to the tibial plafond. Two surgeons employed an open lateral approach for the procedure. The angle bisector method involved using a drill (2.8 mm) and screw (3.5 mm) directed along the bisector of the angle formed between two percutaneously placed K-wires (1.8 mm) at the fixation level, tangent to the anterior and posterior aspects of the fibula and tibia (Figure 1a). Subsequently, CT images of the cadavers were obtained (Figure 1b). The angle between the true centroidal axis (determined by software) and the axis of the screw placed with the angle bisector method was measured. Furthermore, distances between entry points of the centroidal axis and the screw were measured. Distances in millimeters between the positioned K-wires and major neurovascular structures were measured on cadaver dissections. (Sponsored by AOFAS-grant) Results: The mean angle between the centroidal axis and the trajectory of the screw was 2.7 degrees (±2.2, range 0-9.2 degrees) at the 2 cm level and 1.8 degrees (±2.1, 0-7.8 degrees) at the 3.5 cm level. At the 2 cm level, the average distance between the fibular entry points of the centroidal axis and the screw was 1.7 mm (±1.2, range 0-3.2 mm), while at the 3.5 cm level, it was 1.2 mm (±1.3, range 0-2.5 mm). The results exhibited low inter-surgeon variability (ICC > 0.80). The distance between the placed K-wires and major neurovascular structures consistently exceeded 5 mm, ensuring the safety of the technique, as none of these structures incurred damage. Conclusion: Our findings demonstrate that the angle bisector method offers a precise trajectory for syndesmotic fixation, proving its safety and efficacy in surgical applications. It can provide a more precise and patient-specific anatomical trajectory for syndesmotic implant compared to the conventional freehand technique, without increasing fluoroscopy exposure.