ACL injury more than 6 weeks is old, instability is manifested in the following 3 degrees: Severe instability: ACL combined with poor muscle compensation of the knee joint, manifested by walking or jogging in daily life can feel the knee joint misalignment, this misalignment is generally manifested in the femur and tibia of the knee joint left and right misalignment. Moderate instability: ACL rupture combined with moderate muscle compensation, manifested as not daring to accelerate fast running, not daring to stop and turn sharply when running fast. Mild instability: ACL rupture combined with good muscle compensation, manifested by the ability to engage in general sports, the patient can run, carry the ball, but some movements in the game such as jumping up and landing on one foot, using the affected lower limb to support the shot with the healthy foot can not be completed, or to complete a reaction time (reduced motor ability).