Cortices of Fibula and Tibia Can Provide Landmarks for Accurate Syndesmosis Fixation Angle: Computed Tomography Validation of Angle Bisector Method.

Anatomic syndesmosis reduction is necessary to restore ankle biomechanics and prevent poor clinical outcomes, but malreduction can be encountered frequently since the ideal fixation angle varies between patients and fixation levels. This study aimed to validate the angle bisector method to reveal whether it provides an accurate syndesmotic fixation angle that is patient- and level-specific. Lower extremity CT angiography of 50 consecutive patients (25 male, 25 female) without evident ankle pathology were evaluated. The average age was 52.8 (±18, range: 18-75). Lines tangent to anterior and posterior cortices of tibia and fibula were drawn in the axial plane at both 2 cm and 3.5 cm above the ankle joint line. Bisection of the angle formed between these lines was drawn and its relationship with the centroidal axis, which is proposed to be the ideal syndesmotic axis, was evaluated. The angle between the bisector line & the centroidal axis and the distance between their most lateral intersections with the fibula were calculated. The measurements were made by 3 blinded observers. Intra- and interobserver reliability analyses were conducted. The average centroidal axis-bisector angle was 2.1° ± 2.1° at 2 cm and 0.6° ± 1.3° at 3.5 cm level. The average distance to the actual syndesmosis entry point was 1.0 ± 0.9 mm at 2 cm and 0.4 ± 0.4 mm at 3.5 cm level. The values didn't show any significant difference according to gender. Intra- and interobserver reliability analysis showed excellent correlation in all parameters (interclass correlation coefficient > 0.90). Angle bisector method was found strongly reliable providing accurate direction for syndesmotic axis. It can provide a patient- and level-specific angle for the application of syndesmotic implants without increasing the fluoroscopy exposure. Its use can have a broad impact on functional outcomes of ankle injuries by decreasing the malreduction rates. Further cadaveric validation and safety studies should be conducted for possible clinical usage.