First of all, in terms of knee function, knee extension is more important than knee flexion, because if a person has a normal knee extension and a knee flexion of only 90 degrees or so, there is no problem with walking. But even if the knee flexion can go to full angle and the knee extension is 10 degrees short, then the person must walk with a limp. So the focus of our postoperative exercises should be: knee extension! For ACL reconstruction patients, knee extension exercises are even more important, because first of all, many of us take the tendon from the hamstring tendon, which is an injury in itself, so after this injury, we must strengthen the knee extension. Many people will complain of soreness and pulling pain on the back side of the knee joint, which is a normal phenomenon caused by tendon removal, and the patient will feel a little bit more comfortable bending the knee, but over time the tendon removal site will form tough scar tissue, and it will be very difficult to straighten it in the future. Other patients are unable to straighten their knee before surgery because of a stuck or noose meniscus, or swelling, so it is even more important to strike while the iron is hot at an early stage after surgery! The most common method is the “tiger bench” method: the heel of the foot is padded up, and the knee joint is empty, if it can be straightened in this way, and there is some pulling sensation on the back side of the joint, then OK, keep it like this for a long time, and if you can’t stand it anymore, you can come down to take a rest, and then keep it for a long time again. If the above methods can not be straightened, then we should add appropriate pressure sandbags to consolidate the effect. Sandbags usually 5-10 pounds each, you can also use other materials such as rice bags instead. The area of pressure should avoid the location of the patella. Each time at least 30 minutes. For a few patients with severe limitation of knee extension, it is sometimes necessary to use a straight splint to immobilize them after the “tiger bench”. Of course, another method is to lie on the bed with the leg outstretched and then apply sandbags to the ankle. These two methods can be crossed with each other. Flexion: There are various ways to flex the knee, according to the order of the size of the angle on the chart. At the very beginning you can sit like this with the legs hanging down. When the angle is larger, you can use your good foot to help you press. You can usually get to about 90 degrees in the seated position. After that, you can use the supine leg drop, through the effect of gravity to let the calf naturally drop, so usually can reach about 100 degrees. Patients who have difficulty bending their knees can also practice sitting against a wall. When the angle is larger, you can reach an angle close to 120 degrees by holding the leg in a sitting position. The last few dozen degrees can be used to kneeling method, using their own body weight to press down. (Note that patients after posterior cruciate ligament surgery are prohibited from using this method), some patients may feel pain in the posterior side of the joint when kneeling, then it can be changed to the squatting method. Usually early postoperative knee flexion training once a day is enough, each time to fight within 20 minutes to solve the battle, otherwise repeated tossing joints are also prone to cause swelling and pain. Of course, the exercises should be accompanied by ice packs immediately afterward. Most of the patients can return to normal joint mobility in about 2-3 months, if there is no progress for a long time, you should also consult a doctor in time to prevent the occurrence of joint adhesion.