After ACL surgery, the knee joint usually needs to be immobilized for 6 to 8 weeks, and after the immobilization is released, you can start to exercise bending the leg gradually. The anterior cruciate ligament is an important ligament in the knee that prevents the knee from shifting too far forward during movement. Surgery is usually reconstructive and requires a sufficient healing period, so the knee still needs to be immobilized for 6 to 8 weeks after surgery. After the brake is released, the knee can be flexed on its own. In fact, the knee is not immobilized in the straight position after the surgery. At the beginning of the immobilization, the knee is bent at an angle (about 15°), and then the immobilization position is adjusted periodically (gradually increasing the angle of bending) according to the healing of the ligaments, in order to prevent the joint stiffness and ligament damage. After ACL surgery, it is important to follow the doctor’s instructions for functional exercises and not to move the knee blindly on your own.