New landmarks for ideal positioning of syndesmotic screw: a computerised tomography based analysis and radiographic...

A lack of specific intra-operative markers for accurate positioning of the syndesmotic screw can result in its malpositioning. Knowledge of the axial orientation of the syndesmosis can help in reducing this risk of malpositioning of the syndesmotic screw. In this CT-based study, we investigated the axial relationships of intact syndesmoses with various rigid bony landmarks around the ankle joint that were independent of foot and horizontal plane.

We analyzed 126 CT-based studies of uninjured normal ankle joints and defined the following bony landmarks: posteromedial and posterolateral surface of the distal tibia, bimalleolar tips, and anterior and posterior extents of both malleoli. Axial differences between coronal plane through the central axis of syndesmosis and modified coronal planes through these bony landmarks were then measured. Software-based lateral radiographs were created with the reference coronal plane for each radiograph being kept perpendicular to the plane of the viewing screen.

The mean axial differences parting the syndesmotic axis from the modified coronal planes based on distal tibial posteromedial surface, distal tibial posterolateral surface, bimalleolar tips, anterior bimalleolar extents, and posterior bimalleolar extents were - 3.15°, 13.73°, 4.10°, 11.95°, and 12.24°, respectively. With the exception of the posterolateral surface of the distal tibia, all other bony landmarks were radiologically identifiable in the majority of cases.

Our study attempts to provide a solution to the issues related to malpositioning of the syndesmotic screw by providing new bony landmarks that can be clinically and fluoroscopically used for syndesmotic-screw positioning. The relationships of bimalleolar tips, anterior and posterior bimalleolar extents, and the posteromedial surface can be reliably used as landmarks for directing syndesmotic screws.