Knee osteoarthritis that prevalently occurs at the medial compartment is a progressive chronic disorder affecting the articular cartilage of the knee joint, and lead to loss of joint functionality. Valgus braces have been used as a treatment procedure to unload the medial compartment for patients with medial osteoarthritis. Valgus braces through the application of counteracting external valgus moment shift the load from medial compartment towards the lateral compartment. Previous biomechanical studies focused only on the changes in varus moments before and after wearing the brace. The objective of this study was to investigate the influence of opposing external valgus moment applied by knee braces on the lateral tibial cartilage contact conditions using a 3D finite element model of the knee joint. Finite element simulations were performed on the knee joint model without and with the application of opposing valgus moment to mimic the unbraced and braced conditions. Lateral tibial cartilage contact pressures and contact area, and tibial rotation (varus-valgus and internal-external) were estimated for the complete walking gait cycle. The opposing valgus moment increased the maximum contact pressure and contact area on the lateral tibial cartilage compared to the normal gait moment. A peak contact pressure of 8.2 MPa and maximum cartilage loaded area of 28% (loaded cartilage nodes) on the lateral cartilage with the application of external valgus moment were induced at 50% of the gait cycle. The results show that the use of opposing valgus moment may significantly increase the maximum contact pressures and contact area on the lateral tibial cartilage and increases the risk of articular cartilage damage on the lateral compartment.