Manual Stress Ankle Radiography Has Poor Ability to Predict Deep Deltoid Ligament Integrity in a Supination External Rotation Fracture Cohort

Abstract

Stress ankle radiographs are routinely performed to determine deep deltoid ligament integrity in supination external rotation (SER) ankle fractures. However, variability is present in the published data regarding what medial clear space (MCS) value constitutes a positive result. The purposes of the present study were to evaluate the diagnostic accuracy of different MCS cutoff values and determine whether this clinical test could accurately discriminate between patients with and without a deep deltoid ligament disruption. MCS measurements were recorded for stress ankle injury radiographs in an SER ankle fracture cohort. Preoperative ankle magnetic resonance imaging studies, obtained for all patients, were then read independently by 2 musculoskeletal attending radiologists to determine deep deltoid ligament integrity. The MCS measurements were compared with the magnetic resonance imaging diagnosis using receiver operating characteristic analyses to determine the sensitivity, specificity, and optimal data-driven cutoff values. SER II-III patients demonstrated a mean stress MCS distance of 4.3 ± 0.98 mm compared with 5.8 ± 1.76 mm in the SER IV cohort (p < .001). An analysis of differing MCS positive cutoff thresholds revealed that a stress MCS of 5.0 mm maximized the combined sensitivity and specificity of the external rotation test: 65.8% sensitive and 76.5% specific. Using the receiver operating characteristic curve analysis of the MCS measurement, the calculated area under the curve was 0.77, indicating inadequate discriminative ability for diagnosing SER pattern fractures with or without a deep deltoid ligament tear. Judicious use of additional diagnostic testing in patients with a stress MCS result between 4.0 mm and 5.5 mm is warranted.