A mechanical 4-bar knee is a type of prosthetic knee joint used in lower limb prostheses. It is designed to mimic the natural motion of the knee joint during walking, providing a stable and efficient gait for amputees. The 4-bar mechanism consists of four links (bars) connected by pivot joints (hinges). The four links are arranged in a quadrilateral shape, with two opposing links forming the upper and lower thighs of the prosthetic leg, and the other two links forming the upper and lower shanks. The pivot joints are located at the knee joint and ankle joint.