Defining normative side-to-side differences in the distal tibiofibular joint of healthy individuals using weight-bearing CT 3D image analysis.

Background And Purpose: Accurate quantification of bony malalignment within the ankle syndesmosis is crucial in diagnosing syndesmotic instability, especially when subtle. While three-dimensional (3D) measurement techniques using weight-bearing computed tomography (WBCT) have gained popularity, normative bilateral comparative data still need to be established. This study aimed to identify the side-to-side variations and gender differences in the syndesmotic area and volume among individuals without syndesmotic injury using WBCT.

Methods: Retrospective analysis was conducted on bilateral ankle WBCT imaging of 88 individuals who underwent imaging for non-ankle-related injury or pathology. Two-dimensional area (at 1, 3, and 5 cm proximal to the tibial plafond) and three-dimensional volumetric (from 0.5 mm proximal to the tibial plafond and up to 3 and 5 cm proximally) measurements were obtained for bilateral ankles. Mean ( ± SD) values, percentage right-to-left differences, and gender differences were analyzed.

Results: Although there were no significant differences between laterality in any of the measurements, the largest right-to-left difference was 8.9 at the syndesmotic area at 3 cm above the tibial plafond in general. Contrarily, significant gender differences were found in the areas and volumes, with the largest difference observed for the 0.5-5 cm volume (8.41 ± 0.87 vs 7.45 ± 1.47 in male vs female, respectively; P = 0.001).

Conclusion: The mean side-to-site variation in the syndesmotic area and volume among individuals without syndesmotic injury is less than 9 %, and a side-to-side volume difference greater than 19 % might be indicative of abnormality. Additionally, gender-specific differences highlight the importance of considering gender norms in ankle syndesmosis evaluation and the need to use the contralateral side as a comparison.