“Sonanis Tuning Fork Lines”: A New Radiologic Method to Determine Talar Shift, Diastasis, and Displacement of Lateral Malleolus in Ankle Fractures

Abstract

We introduce new “Sonanis” Tuning fork lines (TFL) to be drawn on ankle anterior-posterior (AP) radiographs to diagnose and assess the percentage of the talar shift, diastasis, and displacement of the lateral malleolus fractures. A 3-dimensional (Auto-CAD) of the ankle joint was reconstructed, and TFL were drawn on ankle AP radiographs. In a normal radiograph, the medial surface of the fibula touched the handle of the TFL, and the superior-lateral dome of the talus lies medial to the handle of TFL. In displaced ankle fractures with diastasis and talar shift, this relation is lost. The Talar shift was graded as per the handle of the TFL cutting talar dome. A cohort radiologic study was done by drawing TFL on 100 radiographs, and the results were observed by a senior clinician. Fourteen patients had normal radiographs, and further 33 patients had an ankle fracture with no talar shift. Ankle diastasis with talar shift was seen in 27 cases and they were further graded as: grade 0 (no shift): 0 patients, grade 1 (<25% shift): 15 patients (4%), grade 2 (25-50% shift): 7 patients (1.89%), grade 3 (50% to 75% shift): 1 patient (0.27%), grade 4 (75% to 100% shift): 0 patients (0%), and grade 5 (100% shift): 4 patients (0.6%). We conclude that in a normal ankle AP radiograph it is possible to diagnose and comment on the ankle fractures even if proper ankle mortise views or computed tomography scans were not available.