This study presents the bio-inspired open joint for dynamic robots. Bio-inspired joint contributes to robot performance and understanding living organisms by providing dynamic motion data as the real-world physical twin. The proposed joint structure features the integration of the open joint and ligamentous constraint. In particular, the spherical envelope of the condyles contributes to the rotation other than the pitch rotation. By applying bio-inspired ligament arrangement, the developed knee joint performed pitch and yaw motion. The relationship between the ligament length and joint orientation was derived by forward kinematics. The proposed structure is made from 3D-printed components and can be easily repaired. Verification of the proposed approach includes the qualitative evaluation of Range of Motion (ROM) on the 3D-printed model. The robot joint testbed was also built using four motor-driven tendons. The robot validation tests include the rotational motions around the pitch and yaw axes. The tests showed that the proposed joint structure can be a relevant approach for replicating the ROM of a human knee joint. Future works include the actuation of the joint system and integration into a real robot utilizing kinematic models to derive in-vivo load patterns.