3D model analysis of existing CT syndesmosis measurements

Use of Computed Tomography (CT) to evaluate syndesmotic reduction following injury has significantly increased in recent years. The aim of this study was to compare existing clinical measurements of syndesmotic reduction to gold standard measurements of fibular motion obtained from a full 3D model.

Three common clinical measures for assessing syndesmotic congruity on axial CT slices were identified in the literature. Each measure was manually performed on 170 cadaveric ankle CT scans obtained with variable degrees of simulated syndesmotic displacement. Clinical measures were assessed for intraobserver and interobserver reliability and compared to objective measures of true medial/lateral and anterior/posterior translation and fibular rotation that were obtained from a 3D model. Pearson correlation coefficients (PCC) were computed to determine which clinical measurements were most accurate for describing syndesmotic motion obtained from the 3D model.

All three clinical measurement techniques demonstrated good to excellent interobserver and intraobserver reliability. Medial/lateral displacement of the fibula was best correlated with the difference between the anterior and posterior tibiofibular joint space measurements described by Elgafy et al (PCC = 0.29 small correlation). Anterior/posterior displacement of the fibula was well correlated with the anterior/posterior measurement described by Phisitkul et al (PCC = 0.69 large correlation). Fibular rotation was best correlated with the average of the Elgafy anterior and posterior tibiofibular joint space measurements (PCC = 0.33, moderate correlation). Proximal/ distal displacement of the lateral malleolus was best correlated with the Elgafy posterior tibiofibular joint space measurement (PCC = 0.49, moderate correlation).

While the clinical measurements were adequately reproducible, they showed only moderate to small correlations with the 3D measurements of movement of the fibula in the longitudinal, medial/lateral or rotational directions. The only fibular translation measured by the 3D model that was well described by the three clinical measures was fibular movement in the anterior/ posterior direction. This work demonstrates a need for improved clinical measurements of syndesmotic congruity on axial CT scans to serve as surrogates for the true movement of the fibula.