The tibiofibular line: an anatomical feature to diagnose syndesmosis malposition.

Background: Medical imaging of the distal tibiofibular joint requires reliable and simple tools to identify disruption of the syndesmosis. We present an anatomical feature, the "tibiofibular line," which appears on axial computed tomography (CT) images of normal ankles. This feature is a straight line that connects the anterolateral surface of the fibula with the anterolateral tubercle of the tibia at the level of the ankle syndesmosis. The purpose of this study was, first, to demonstrate that this line is a reliable anatomical feature in normal ankles and, second, to demonstrate that this line is displaced with diastasis or malrotation of the syndesmosis.

Methods: A series of 150 normal ankle CTs were collected, negative for history of ankle injury with a normal tibiofibular overlap and clear space. Thirty ankles with a displaced syndesmosis were identified by history, CT, and abnormal tibiofibular overlap and clear space parameters. The tibiofibular line was applied to both groups and measured for its distance displaced from the anterior tibial tubercle.

Results: All CT images in the normal ankle group had a tibiofibular line within 2 mm of the anterior tibial tubercle (77% of the tibiofibular lines were within 0 mm, 19% were within 1 mm, and 4% were within 2 mm). The tibiofibular line in the injured group was displaced anteriorly by 4 to 19 mm (minimum to maximum) from the tibial tubercle (P < .0001).

Conclusion: The tibiofibular line was a normal anatomical feature that could be used to identify displacement of the distal tibiofibular syndesmosis.

Level Of Evidence: Level III, comparative series.