Radiological indicator of reduction adequacy during ankle syndesmosis surgery: A computational cadaveric study.

PURPOSE: We introduced the intraoperative radiological indicator to assess the reduction adequacy without additional procedure or instrument, and propose the optimal syndesmotic screw trajectory.

METHODS

Thirty adult cadavers (15 males and 15 females) without ankle problems were enrolled and subjected to continuous 0.75 mm-slice computed tomography (CT) scans. CT images were imported into Mimics® software to reconstruct three-dimensional (3D) model of ankle. Using free 360° rotations with magnification, the 3D mutual relationships of ankle syndesmosis were assessed, and the fibular congruency of incisura was evaluated to determine the optimal screw trajectory. By reformatting the CT scanning plane along the screw direction, the coronal relation of ankle syndesmosis was evaluated to verify the distance between the adjacent bones.

RESULTS

The fibula was placed in the concentric position of fibular incisura in the 20 models (concentric group) and 40 models, in an eccentric position (eccentric group). Despite this variant, all fibulas were changed into the concentric position in the proximal part of syndesmotic footprint, which might be the ideal height for syndesmotic screw in our study. The fibular bisecting screw trajectory associated with the ideal height of screw was parallel to the ground if the tibial tubercle was directed to the superior and nearly vertical to the ground floor (TT view). Through the reformatted scanning plane parallel to the screw, the lateral border of talus was always placed more medial than the lateral border of distal tibia in the coronal image. All models had a perfectly equidistant and parallel joint space except the medial aspect.

CONCLUSION

The lateral border of talus in the TT view was intraoperatively used as the radiological indicator for ankle syndesmosis widening because it was always placed more medial than the lateral border of distal tibia. The optimal syndesmotic screw trajectory was placed around the proximal syndesmotic footprint and parallel to the ground via the TT view.