Validity of the Center-Center Method for Syndesmotic Fixation Axis Against the Trans-Syndesmotic Axis: A Cross-Sectional Study

Abstract

Category: Trauma; Ankle Introduction/Purpose: In surgery for ankle fractures with tibiofibular diastasis, it is important to vertically grasp the distal tibiofibular joint. However, it is difficult to do that because the tibiofibular joint surface is not under direct vision. Center-center method (CC) is an intraoperative fluoroscopic technique to determine the position of the syndesmotic clamp. CC has been reported to reduce the risk of syndesmotic malreduction, but It is unclear whether the axis by CC (CC axis) coincides with the axis perpendicular to the distal tibiofibular joint (trans-syndesmosis axis: TS axis). Therefore, the present study aims to 1) measure the difference between the CC axis and TS axis, and 2) compare the measured values when CC is performed at different distances from the ankle joint surface. Methods: The subjects were 150 patients who underwent CT scans for ankle joint disease and lower extremity trauma. CC is a method in which the ankle joint is rotated, and the midpoint of the anteroposterior margin of the tibia and fibula is superimposed by fluoroscopy. In the present study, CC was performed using Digitally reconstructed radiography (DRR) created from a CT image. At the ankle joint surface (0mm), CC axis and TS axis were projected onto the CT axis linked with DRR. The angle between the axes was measured (inter-axes angle). Also, the distance of the intersection of these axes through the medial cortex of the tibia was measured (inter-axes distance). It was also performed at 10mm and 20mm proximal to the ankle joint surface. One-way repeated measures analysis of variance and the post hoc Bonferroni tests were used to compare the measured values' difference according to the articular surface's height. Results: Overall, the TS axis was externally rotated relative to the CC axis, with a mean inter-axes angle of 8.5±6.8degrees. The inter-axes angle of 0mm, 10mm, and 20mm were 1.9±4.0degrees, 10±5.3degrees, and 13±5.1degrees, respectively (p < 0.001). Also, the intersection point of the TS axis with the medial tibial cortex was anterior to the intersection of the CC axis, with an inter-axes distance of 7.7±6.3mm overall. The inter-axes distance of 0mm, 10mm, and 20mm were 2.0±4.2mm, 9.0±4.9mm, and 11.3±5.2mm, respectively (p < 0.001). Both the inter-axes angle and the inter-axes distance were larger when the CC method was performed higher to the tibial plafond (P < .001), with the post hoc tests showing significant differences among all heights. Conclusion: The TS axis was externally rotated to the CC axis and positioned slightly anteriorly. Also, the inter-axes angle and distance were larger when the CC method was performed higher to the tibial plafond. If the surgeon aimed to clamp the syndesmosis along the TS axis, the CC method should be applied closer to the ankle joint surface, and the medial tip of the forceps be placed slightly anterior to the point determined by the CC axis.