Anatomical landmarks for optimal insertion of the syndesmotic screw

Abstract

Discussions about the optimal syndesmotic screw (SS) placement deal primarily with its biomechanical aspects. The aim of this article is to point out the anatomical aspects that have so far been mentioned only marginally. Optimal SS placement is dictated basically by three anatomical parameters that may be easily used intraoperatively without any angular measurements or 3D imaging: (1) the level of screw placement, (2) the insertion point at the lateral malleolar crest (LMC), and (3) the screw trajectory through the distal fibula and tibia. The proximal height is limited by concavity of the fibular notch (FN), while the distal height is limited by the extension of the superior recess of the ankle joint cavity. Therefore, the SS is optimally inserted through the concave surface of FN and above the superior synovial recess – between 2 and 3 cm above the ankle joint line. A more distal SS placement results in a higher rigidity of the tibiofibular mortise and lower bending force on the distal fibula. The LCM on the outer aspect of distal fibula is an ideal landmark for insertion of SS in the antero-posterior direction. In the interval of 20–25 mm proximal to the ankle joint line, the LMC may be used as an entry point. If the SS is inserted more proximally than 25 mm above the joint line, the ideal entry point lies 1 to 2 mm posterior to the LMC to ensure its trajectory through the distal fibula and fibular notch in a center-center direction. If the screw trajectory follows the direction of a reduction clamp that is placed close to the tip of the distal tibia and fibula along the axis of the ankle joint, a center-center trajectory in the distal tibia will be achieved without any angular measurements.