Since Dr. Janos von Ertl first performed it, the osteomyoplastic transtibial amputation has truly become a game changer in its field. Although less common, the osteomyoplastic amputation, also known as the Ertl, has been shown to have many physiological benefits when compared to the traditional long posterior flap method. These benefits include less chance of developing bone spurs and increased postoperative function. In previous research, transtibial amputees have been shown to make roughly 50 sit-to-stand transitions per day, and have been shown to bear more weight on their intact leg during these transitions. These asymmetries can cause shifts outside of the base of support and may lead to falls. In this study, we compared the differences in joint angles of the hip, knee, and ankle as well as the excursion in center of pressure (COP) in the x and y range between individuals with an osteomyoplastic amputation (n=7) to a healthy control (n=9) during sit-to-stand (STS) transitions. A Vicon Nexus 1.8.5 system collected joint angle data and two in-ground force plates collected COP data. These data were analyzed using measures ANOVA (SPSS, 20.0, alpha=.05). We found statistically significant differences in knee and ankle joint angles, ankle range of motion, and COP excursion in the x and y range for both sitting and standing transitions. These data may suggest that the lack of dorsiflexion in prosthetic ankle joints lead to instability during STS transitions.