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Category: Ankle, Trauma Introduction/Purpose: Distal tibio-fibular syndesmotic reduction (SR) is an independent predictor of good functional outcome following ankle surgery. Classic intraoperative fluoroscopic parameters have shown to be poor predictors of distal SR. Syndesmotic malreduction (S-MR) has been reported up to 52% of surgically treated patients. Grenier et al proposed the Anteroposterior Tibio Fibular Ratio (APTF) to evaluate normal sagittal syndesmotic anatomy, showing good interobserver agreement and high correlation between both sides in normal ankles. We propose the use of the comparative APTF index (cAPTF), calculated as the absolute difference of APTF index between the normal and surgically treated ankle, to guide intraoperative sagittal SR. The aim of this study was to determine the capability of the intraoperative cAPTF to predict S-MR. Methods: Prospective observational study. Patients who required syndesmotic fixation for an unstable ankle fracture and who had a contralateral healthy ankle were prospectively enrolled. Intraoperative APTF was measured under fluoroscopy in both ankles according to Grenier et al and the cAPTF was calculated. No surgeons were informed of APTF measurements during the procedure. Bilateral postoperative CT was obtained, and quality of SR was evaluated using the method described by Dikos et al. To estimate the discriminatory power of the cAPTF, a receiver operative characteristic (ROC) curve was obtained and the area under the curve was calculated. Youden index was used to determine the ideal cAPTF cut-off value for S-MR and its sensitivity, specificity, positive likelihood ratio (LR+) and negative probability (LR-) were calculated. Results: Forty-seven patients were enrolled. Sixteen (34%) had S-MR on the postoperative CT. The cAPTF varied between 0.005 and 0.435. The cAPTF cut-off value to predict S-MR was 0.161. A cAPTF value greater than 0.161 had Sensitivity 100%; specificity 94%; LR+ 15.50; and LR- 0.06, for predicting malreduction of the syndesmosis. The area under the ROC curve was 0.99. Conclusion: Intraoperative cAPTF index demonstrated excellent discriminatory power for predicting syndesmotic malreduction. We propose the routine use of this new method to improve the results of syndesmotic reduction.

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