CT scan assessment of the syndesmosis: a new reproducible method

Anatomic reduction of the fibula with regard to the tibia is the goal when treating syndesmotic injuries. No objective method exists to describe the distal tibiofibular relationship. The primary and secondary objectives of this study was to describe and validate radiologic measurements of the syndesmosis and to establish a set of normal values, respectively.

A set of 6 measurements and 2 angles were defined on axial computed tomography scans. These measures describe distal tibiofibular anatomy in rotation, lateral translation, and anteroposterior position. A series of 100 ankle computed tomography scans were measured by 2 evaluators. Interobserver reliability was assessed on a subset of 30 scans by 3 different evaluators. Measurements were repeated 6 weeks later by 2 evaluators for intraobserver reliability. All correlations were evaluated with intraclass correlation coefficients.

Good correlations for nearly all measurements were found, with intraclass correlation coefficients over 0.5. The lateral translation was the most reliable measure with a mean value of 2.8 mm. The mean ratio of anterior tibiofibular distance to posterior tibiofibular distance was 0.54. Proximal to tibial plafond, the fibula is internally rotated 8.7 degrees and at the talar dome level it is in 6.9 degrees of external rotation.

Several studies have shown that the reduction of the syndesmosis is essential to restore normal ankle mechanics and prevent secondary degenerative changes. The evaluation criteria developed in this study can give the surgeon a guideline for evaluating syndesmosis anatomy with reliable parameters. Concerning the normal range of motion, our radiologic measurements of 100 normal ankles showed that a significant amount of variability exists in the uninjured distal tibiofibular relationship.