A computed tomography evaluation of two hundred normal ankles, to ascertain what anatomical landmarks to use when compressing or placing an ankle syndesmosis screw

• Ankle fractures with associated syndesmotic injury have more pain and poorer function that those without syndesmotic injury.
• High syndesmotic malreduction rates are associated with poor functional outcome.
• Lateral apex of fibula and area of the medial malleolus just anterior to its midline can be used as landmarks when inserting trans-syndesmotic screws.
• The reduction clamp should always be placed along the centroidal axis to avoid anteriorposterior instability.
• This study conflicts with current AO teaching recommending screw insertion at 25–30 degrees relative to the coronal plane of the ankle.

Classical AO teaching recommends that a syndesmosis screw should be inserted at 25–30 degrees to the coronal plane of the ankle. Accurately judging the 25/30 degree angle can be difficult, resulting in poor operative reduction of syndesmosis injuries.The CT scans of 200 normal ankles were retrospectively examined. The centroid of the fibula and tibia in the axial plane 15 mm proximal to the talar dome was calculated. A force vector between the centroid of the fibula and the tibia in the axial plane should not displace the fibula relative to the tibia when surfaces are parallel. Therefore, a line connecting the two centroids was postulated to be the ideal syndesmosis line. This line was shown to pass through the fibula within 2.5 mm of the lateral cortical apex of the fibula and the anterior half of the medial malleolus in 100% of the ankles studied.The results support the concept that in the operatively reduced syndesmosis, the anterior half of the medial malleolus can be used as a reliable guide for aiming the syndesmosis drill hole, provided that the fibular entry point is at/or adjacent to the lateral fibular apex. The screw should also remain parallel to the tibial plafond in the coronal plane.