Weightbearing Computed Tomography Evaluation of Acute SER4a Ankle Fractures

Background: Supination external rotation (SER) fibula fractures with abnormal medial clear space (MCS) on stress radiographs that normalizes with weightbearing radiographs, termed SER4a ankle fractures, pose a challenge in treatment decision making. This study aims to quantify differences in joint contact area, tibiotalar rotation, and translation using weightbearing computed tomography (CT) scans in SER4a ankle fractures. Methods: Between November 2022 and September 2023, patients presenting with isolated Weber B fibula fractures were evaluated for inclusion. Adult patients presenting within 10 days of injury with an SER4a ankle fracture, and no history of ankle fractures or surgery, were included. Ten patients were enrolled and underwent bilateral ankle weightbearing CT scans. Disior Bonelogic Software was used to quantify joint contact area, tibiotalar rotation, and translation, with the uninjured ankle serving as the control. Results: Ten patients (4 male, 6 female) with an average age of 51 years were included. The average MCS measured 2.5 mm (SD 0.36) on weightbearing and 5.7 mm (SD 0.67) on stress radiographs. The difference in joint contact area between injured and healthy joints was 12.2 mm(2) (P = .085). Axial tibiotalar joint rotation averaged 6.6 degrees of increased external rotation on the injured extremity (P < .001). The mediolateral distance between the center of the tibial plafond and center of the talar dome was increased 1.0 mm in the injured extremity (P < .05). Conclusion: In this study evaluating 10 patients with acute SER4a ankle fractures, no difference in joint contact area was found between individuals' healthy and injured ankles. However, differences in external rotation and lateral translation of the talus were observed on the injured ankle. The clinical effects of these tibiotalar rotational and translational changes are unknown. Clinical Relevance: This study provides insight regarding in vivo changes in 3-dimensional alignment of SER4a ankle fractures that may influence future management of these fractures.