Measuring Deltoid Insufficiency After Supination-External Rotation Ankle Fracture With Lateral Talar Subluxation on Gravity Stress View

Background: Stress-view radiographs are frequently obtained to evaluate supination-external rotation (SER) variant ankle fractures. Measurement of the ankle medial clear space (MCS) is a surrogate of medial structure integrity as part of overall ankle stability. Measurement of the lateral talus displacement with respect to the incisura may be a sensitive and specific method to assess joint subluxation. Methods: Retrospective review of acute SER-variant isolated lateral malleolar fractures with gravity stress views (GSVs) were performed for 103 patients. GSV analysis was performed with standardized measurements of the MCS, superior clear space (SCS), and 2 new novel measurements of lateral talus subluxation (LTS). Decision for surgery was obtained by surgeons who reviewed masked injury radiographs for predictive performance analysis of the LTS vs MCS. Results: MCS, SCS, and LTS measurements were performed on 103 patients. Mean MCS, SCS, and LTS within the operative group was increased. MCS ≥5 mm and LTS >4 mm had equal sensitivity (95%), with higher specificity for LTS (75% vs 60%). Receiver operating characteristic analysis demonstrates an area under the curve of 0.786 for MCS ≥5 mm vs 0.918 for LTS >4 mm. Conclusion: We found LTS to be superior to MCS for medial ankle structure stability on gravity stress views of SER-variant ankle fractures. We propose this as a useful tool for clinicians to consider when evaluating SER-variant ankle fractures. Level of Evidence: Level II, prospective comparative study of radiographs.