Category: Trauma Introduction/Purpose: Ultrasonography is increasingly used to evaluate the stability of various joint in the field of foot and ankle. This study aims to assess and compare the Lisfranc joint stability under stimulated weight bearing condition among progressive stages of Lisfranc ligamentous complex injuries. All the measurements were assessed using ultrasonography, fluoroscopy, and direct open measurement. We hypothesize that there is a correlation between ultrasonographic and fluoroscopic measurements, or between ultrasonographic and direct open measurements when performing stress evaluation of the Lisfranc instability. Methods: Twelve fresh below-knee amputated cadaveric specimens underwent ultrasound, fluoroscopic, and direct gross evaluation of the Lisfranc stability under simulated weight bearing condition. The assessment was first performed with all Lisfranc ligamentous complex intact and thereafter with sequential transection of the dorsal Lisfranc ligament, interosseous Lisfranc ligament, and plantar Lisfranc ligament. The simulated weight bearing condition was performed with 600N of force. The distances evaluated during the experimental set up were C1-M1, C2-M2, C1-M2, C1-C2 and M1-M2. All measurements were recorded in millimeter (mm). The ultrasound machine (GE, LOGIQ E-9 ultrasound machine, Chicago, Illinois, USA) was used to assess the Lisfranc stability by measuring the distances between the hyperechoic bone contours or the pre-defined landmark of the metatarsal and cuneiform bones. Correlations between 1) Ultrasound and fluoroscopic measurements, 2) Ultrasound and direct open measurements, and 3) Fluoroscopic and direct open measurements were evaluated using Pearson correlations coefficient. Results: Strong positive correlations between ultrasonographic and direct open measurements were found when assessed for C1-M1, C1-M2, C1-C2, M1-M2 (Pearson's correlation ranged from 0.73-0.97, p-values <0.001). Strong positive correlations between ultrasonographic and fluoroscopic measurements were found when assessed for C1-M1 from dorsal, medial, and plantar aspect (Pearson's correlation ranged from 0.75-0.90, p-values <0.001). Strong positive correlations between fluoroscopic and direct open measurements were found when assessed for C1-M1, C1-M2, C2-M2, M1-M2 (Pearson's correlation ranged from 0.77-0.93, p-values <0.001). Inter-rater and intra-rater reliability for the ultrasonographic measurements between the MSK radiologist (TK) and the foot and ankle surgeon (JS) were substantial (ICC ranged from 0.81-0.98). Conclusion: Ultrasonography is a reliable and reproducible tool for diagnosing Lisfranc ligamentous complex injuries. Both ultrasonographic and fluoroscopic measurements appear to strongly correlate with values measured by direct open measurement. Based on these data, ultrasonography is likely to become a valuable point of care diagnostic tool due to its ability to readily and dynamically evaluate suspected Lisfranc ligamentous complex injuries, without radiation exposure.