MRI Findings in Patients with Discordant Results Between Gravity Test and Weight-Bearing Stress Views in Isolated Supination-External Rotation Fibular Fracture
Authors: Piga Camilo , Turner Felipe , Herrera Valentina F. , Pino Cristobal F. Del , Bastias Gonzalo F. , Filippi Jorge 
Published: November 2022

Category: Trauma Introduction/Purpose: Medial and syndesmotic stability evaluation of isolated supination-external rotation fibula fractures (ISER) is critical to determine surgical conduct. However, there is no agreement on the best method to diagnose instability preoperatively. This problem is especially relevant in those with less than 2mm displacement in non-weightbearing radiographs. Different radiographic stress methods have been proposed: external rotation, weightbearing x-rays (WBx), and gravity stress radiographs (GSx). Likewise, the literature describes the use of ultrasound and magnetic resonance imaging (MRI) as complementary studies. To our knowledge, no studies have described the MRI findings in patients with discordant results between GSx and WBx views. Purpose: To analyze the imaging findings in WBx, GSx, and MRI in a consecutive group of patients with ISER with discordant results on stress views. Methods: For two years and prospectively, consecutive patients treated in a Level 1 trauma center were enrolled, performing the following imaging study protocol:- All patients with ISER fractures with a congruent tibiotalar joint on non-weightbearing radiographs underwent a bilateral WBx and GSx.- When there was a discordant result between WBx and GSx, MRI was taken. A retrospective analysis of the patients who had a complete study was carried out, considering the radiological findings and measurements. Measurements on radiographs were performed by six physicians (2 general practitioners, two trauma residents, and two ankle and foot subspecialists). One musculoskeletal radiologist analyzed the MRIs. The following parameters were measured, medial clear space (MCS), superior clear space (SCS), and tibiofibular clear space (TFCS). Inter-observer agreement in radiographs was analyzed using the intra-class correlation coefficient. Differences between groups were evaluated by t-student for independent samples, considering α <=5% significant. Results: Thirty-four patients were recruited. Interobserver agreement was good to excellent on all radiographic measurements. For all the measurements in the WBx, there were no significant differences between the injured and the healthy side. Average of MCS 2.51, SCS 3.07 and TFCS 3.74 mm for the uninjured side; and MCS 2.51, SCS 3.12, and TFCS 3.67 mm for the injured side. In the GSx, significant differences were observed for all measurements between the fractured and the healthy side. Average of MCS 3.55, SCS 3.85, and TFCS 3.89 for the healthy side; and MCS 5.87, SCS 4.25, and TFCS 4.44 for the injured side.100% of GSx and 0% of WBx met instability criteria (more than 2 mm compared to the healthy side). None of the MRIs showed a complete lesion of the deep deltoid ligament nor syndesmal complex. Conclusion: MRI did not demonstrate a complete deltoid nor syndesmal lesion in any patient with ISER fracture with normal WBx and altered GSx. A positive GSx does not correlate with MRI findings in patients with a non-displaced WBx study.