Comparison of External Torque to Axial Loading in Detecting 3-Dimensional Displacement of Syndesmotic Ankle Injuries.

Abstract

Current imaging techniques try to quantify 3-dimensional displacement of syndesmotic ankle injuries using 2-dimensional measurements, which may obscure an exact diagnosis. Therefore, our aim was to determine 3-dimensional displacement of syndesmotic ankle injuries under load and torque using a weightbearing computed tomography (WBCT) and to assess the relation with previously established 2-dimensional measurements. Seven paired cadaver specimens were mounted into a radiolucent frame. WBCT scans were obtained to generate 3-dimensional models after different patterns of axial load (0 kg, 85 kg) combined with external torque (0, 10 Nm). Sequential imaging was repeated in ankles containing intact syndesmotic ligaments, sectioning of the anterior inferior tibiofibular ligament (AITFL; condition 1A), deltoid ligament (DL; condition 1B), combined AITFL+DL (condition 2), and AITFl+DL+interosseous membrane (condition 3). Reference anatomical landmarks were established relative to the intact position of the fibula to quantify displacement. A subsequent correlation analysis was performed between the obtained 2- and 3-dimensional measurements. Axial load increased lateral translation (mean = -0.9 mm, 95% confidence interval [CI]: 1.3, -0.1) significantly in condition 2 relative to the intact ankle (P < .05) but did not demonstrate other significant displacements. External torque increased displacement significantly in all directions (P < .05), except for dorsal translation of the fibula (P > .05). The highest displacement could be detected when external torque was applied in condition 3 and consisted of posterior translation (mean = -3.1 mm; 95% CI: -4.8, -2.7) and external rotation (mean = -4.7 degrees; 95% CI: -5.6, -2.9). Pearson correlation coefficients between the 2-dimensional and 3-dimensional measurements were moderate and ranged from 0.31 to 0.56 (P < .05). External torque demonstrated superiority over axial load in detecting syndesmotic ankle instability. Axial load increased lateral translation; however, differences were submillimeter in magnitude until torque was applied. A moderate correlation was found with previously established 2-dimensional measurements. In clinical practice these findings substantiate application of external torque in current imaging modalities to improve detection of syndesmotic ankle injuries.