Incisura tangent method to determine the transsyndesmotic axis for syndesmotic fixation

Clamping along the transsyndesmotic (TS) axis decreases the risk of malreduction when reducing syndesmotic diastasis. We aimed to measure the difference between the TS axis and the axis determined by the newly proposed fluoroscopic incisura tangent (IT) method. The measurements were compared to those between the TS axis and those based on the center–center (CC) and talar dome lateral (TL) methods. We analyzed computed tomographic images of 43 normal ankles. The IT view was simulated using a digitally reconstructed radiograph, in which the anterior and posterior fibular incisura tubercles overlapped on the internally rotated anteroposterior view. The interaxis angle between the TS and the axes determined by the IT method was measured on the axial computed tomographic image corresponding to the radiographic image. The same procedure was repeated using the CC and TL methods. The measured values were compared between the three methods using a one-factor analysis of variance. Furthermore, the measurements of the anteverted and retroverted incisurae were compared for each fluoroscopic method. The mean interaxis angles between the TS were − 0.5 degrees, 6.3 degrees, and − 1.8 degrees for the IT, CC, and TL methods, respectively, with a significantly larger value for the CC method than for the IT and TL methods (P