After surgery, the first thing that comes to mind for many ACL injury patients is how to practice bending the knee. Perhaps it is because they have seen many “fork friends” sharing that it is very painful to break the leg and very difficult to bend the leg, so they will focus on “breaking the leg”, after a month, they will find a problem. Therefore, they will focus on “breaking the leg”, and after a month, they will find a problem, that is, the knee can not be straightened. In fact, the function of knee extension is more important than the function of knee flexion, because if the knee is not fully extended, you will definitely limp. That’s why in the postoperative period, we all put extra emphasis on the function of knee extension. We not only want the ability to straighten the knee, but also the ability to hyperextend the knee. If we have 0° of knee extension, then we have about 7° of hyperextension. Knee hyperextension also means that your knee and ankle are not in a straight line and the knee sits behind the ankle. Why is it hyperextended? In the early stages of an ACL injury, almost all patients will experience severe swelling of the knee. The joint capsule of our knee is looser at an angle of 30°, so many patients like to rest at this angle and like to sleep with a pillow under the knee, then over time, the knee cannot be straightened. In knee injuries, most will be accompanied by meniscus or cartilage damage, resulting in intra-articular compression (e.g., joint strangulation caused by meniscus barrel shank-like tear), and then the joint will also show significant limitation of movement. Therefore, in the early postoperative period, we need to actively practice straightening. After ACL reconstruction, even though it is a minimally invasive surgery, a common phenomenon after arthroscopic surgery is scarring. If we don’t practice knee extension at an early stage, some of the scarring will grow from the reconstructed ACL anteriorly to the intercondylar fossa, which will form a placeholder (e.g., Cyclops’ lesion) in the long run, resulting in dysfunction of the knee extension function. Most of the grafts utilized for ACL reconstruction are autologous popliteus tendons, and the removal of the tendon is equivalent to a single injury, and the management of this injury is similar to that of a muscle strain, which is early immobilization in the extensor position to prevent healing of the scar contracture. Many patients prefer to rest with their knees slightly flexed after surgery, which over time can result in limited knee extension. How to practice terminal knee extension? 1.Sitting position passive extension Sit on the bed and use a chair to ginger the affected leg up to the level. Make sure your toes are pointing up in a neutral position. Place a sandbag on top of the knee joint for 5-10 min. ice packs can be used for pain. 2.Passive straightening in prone position Lie down on the bed and move the knee out of the edge of the bed, you can put a towel above the knee. If acceptable, you can tie a sandbag around the ankle and maintain it for 5-10min. ice packs can be used if pain occurs. 3, elastic band resistance to stretching the knee Use elastic band set above the knee joint, the other end of the tie and the door or post fixed. Quadriceps contraction, straighten the knee, so that the heel to the ground, maintain 3 seconds, 10 a group, do 3 groups. 4, bouncy ball resistance knee extension Stand against the wall, make sure your heels can touch the wall. Place a small bouncy ball behind your knee. Quadriceps muscle contraction, force the knee straight, maintain 3 seconds, 10 a group, do 3 groups. In fact, the methods of postoperative knee exercises are more or less the same, to learn more about orthopedic rehabilitation please go to the Department of Joint and Orthopedic Diseases of Changhai Hospital.