Prosthetic knee joint is very important for patients with thigh amputation. The movement function of human knee joint is very complex, and the types and varieties of prosthetic knee joint are the most in all prosthetic shopping. Knee joint is an important functional component of knee prosthesis, thigh prosthesis and hip and thigh prosthesis, and it is also the most complex component. The most basic requirement of prosthetic limb for knee joint function is that the knee joint can keep stable in the support period, and can bend the knee in the swing period. There are many kinds of knee joints with different functions. According to the number of rotation axis, knee joint is divided into uniaxial knee joint and multi axis knee joint. According to the stability control method during the support period, the knee joint is divided into manual locking joint, load-bearing self-locking joint and geometric locking joint. According to the swing period control method, the knee joint is divided into simple swing joint, friction control joint, pneumatic joint, hydraulic joint and microelectronic control joint. According to the different materials, there are single alloy steel, stainless steel, titanium alloy knee joint, but also aluminum alloy and stainless steel, carbon fiber and stainless steel in different forms of knee joint. For the long stump thigh prosthesis and knee amputation prosthesis, there are specially designed knee amputated joints.

The stability of the prosthesis knee joint should be ensured during the supporting period, and appropriate knee torque should be provided during the swing period to realize flexible and natural swing. When walking, when the foot is off the ground and enters the swing period, the movement of the lower leg depends on the swing of the thigh and the torque of the knee joint. The magnitude and mode of knee joint torque are related to walking speed, road condition and human parameters. The knee joint torque can be provided by friction force, spring force, pneumatic device and hydraulic device. But they can only be set once when the prosthesis is assembled according to the situation of the amputee.

If the joint damping can not be changed, the prosthesis can not change with the gait speed of the healthy limb, resulting in asymmetric gait and increased energy consumption of amputees, which will cause great discomfort. The traditional simple prosthesis uses mechanical damping, and its size cannot be adjusted or automatically changed with the walking speed. Therefore, the rotation speed of the knee joint in the flexion and extension period of the prosthetic limb in the gait swing period is asymmetric with that of the healthy limb. The stability of the prosthetic limb in the standing period is mainly guaranteed by the self-locking device or the manual lock. In the 1960s and 1970s, hydraulic / pneumatic devices were used as damping elements in the prosthetic knee joint. The swing speed can be controlled by the hydraulic or pneumatic cylinder in the knee joint to meet the needs of the amputee to speed up or slow down.