The additional value of gravity stress radiographs in predicting deep deltoid ligament integrity in supination external rotation ankle fractures

Objectives Goal of this study was to investigate whether a gravity stress radiograph is beneficial in determining instability in Supination-External rotation (SER)-type ankle fractures without a medial fracture. Methods 39 Patients with a SER-type ankle fracture without a medial or posterior fracture and medial clear space (MCS) < 6 mm at regular mortise view were included. A gravity stress radiograph and Magnetic Resonance imaging (MRI)-scan were made. The MCS measurements of the regular and gravity stress radiographs were compared with the MRI findings (set as reference standard) to determine the sensitivity, specificity, and positive (PPV) and negative (NPV) predictive values as indication for a complete deltoid ligament rupture. Results Mean MCS at regular mortise views was 3.11 (range 1.73–5.93) mm, compared to 4.54 (range 2.33–10.40) mm at gravity stress radiographs. With MCS ≥ 4 mm as threshold for predicting a complete rupture at regular ankle mortise views the sensitivity was 66.7, specificity 91.7, PPV 40.0 and NPV 97.0. Gravity stress radiographs with MCS ≥ 6 mm as threshold led to a sensitivity of 100, specificity 91.7, PPV 50.0 and NPV 100. Conclusion Gravity stress radiographs have more discriminative ability for diagnosing SER-type fractures with or without a complete deltoid ligament tear than regular ankle mortise views.