Category: Midfoot/Forefoot; Bunion 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 sesamoid position and rotation under stimulated weight bearing condition compared to the standard weight-bearing imaging. All the measurements were assessed using ultrasonography, fluoroscopy, and direct gross measurement under weight-bearing condition. We hypothesize that there is a correlation between ultrasonographic and fluoroscopic position and rotation measurements, or between ultrasonographic and direct gross measurements. Methods: Fifteen fresh below-knee amputated cadaveric specimens were simulated with 600N force weight bearing condition. The data of sesamoid rotational and metatarsal rotation were measured under ultrasound (GE, LOGIQ E-9 ultrasound machine, Chicago, Illinois, USA), fluoroscopy, and direct measurement method. And also, joint congruity and grading of sesamoid position were subjectively evaluated under three methods by investigators. The set-up axis of rotation measuring was controlled by digital Halo machine. Correlations of the sesamoid and metatarsal rotation on each method were analyzed using Pearson's correlations. The agreement of joint congruity and grading of sesamoid position on each method were described. Results: A total of 15 feet from 15 cadavers were included to the study. The correlation of sesamoid and metatarsal rotation between ultrasonography and fluoroscopy were 0.78 and 0.58, respectively. The correlation of sesamoid and metatarsal rotation between ultrasonography and gross measurement were 0.88 and 0.74, respectively. The correlation of sesamoid and metatarsal rotation between fluoroscopy and gross measurement were 0.65 and 0.47, respectively. For joint congruity evaluation, there were 100% agreement between fluoroscopy and gross measurement and 93.3% agreement between ultrasonography and gross measurement. For sesamoid position, there was 7% agreement between ultrasonography and fluoroscopy. Inter- and intra- observer reliability between the MSK radiologist and the foot-ankle surgeon were substantial. Conclusion: Weight-bearing ultrasonography is ability to assess the grading of sesamoid and metatarsal rotation including joint congruity assessment when compared with fluoroscopy. However, the sesamoid position could not be evaluated by ultrasonography. The benefits of non-radiation hazard and mobile device usage could allow investigator to easily evaluate deformity in the clinic.