This paper evaluates biomechanical characteristics of artificial elbow joints. To enhance the durability of the joint components, it is important to evaluate the mechanical condition at the bone-joint interface. In this report, we examined the effect of torque produced by the biceps with a three-dimensional model instead of the two-dimensional model used by our previous study. This paper proposes a three-dimensional mathematical model which includes the minimum number of muscles to maintain a balanced arm posture. Calculation of the reaction forces and torque at the elbow joint was done with a 10N load applied at the hand. Stress analysis was then performed using a finite element model composed of the ulna and radius for the lower arm. This study focuses on the stress produced inside the bony tissue around the joint component at the ulna side. The result shows the lateral force of biceps has positive relation to the stress value.