Currently, the ACL is reconstructed using “autologous or allogeneic tendons”, so there are different “tendons” that can be taken and different surgical approaches. At one time, the “popular” method was to take the middle 1/3 of the patellar tendon (the thick, strong tendon attached underneath the patella) and use it as the material. However, post-operative pain in the anterior patellar region and loss of knee extension are common, so this is less and less commonly done nowadays, unless specifically needed. Currently, the most used tendon is the tendon of your own N cord muscle. The so-called N cord muscle is a large muscle group at the back of the thigh responsible for bending the knee joint, and you can feel the N cord muscle group at the back of the thigh contract and harden when you actively bend the leg with force. When the new ACL is reconstructed, the two tendons of the medial N cord muscle are taken, folded and braided to make the ligament. This is why some patients feel pain on the back side of the knee when actively bending the leg after surgery, because the tendons there take some time to heal. This is because it takes some time for the tendon to heal, and until it has healed, active force can be painful. Of course, there are other people who use other people’s allograft tendons and tendons from other parts of the body to make ligaments. There are also artificial materials used to make new ACLs, which are not described here. After the tendon is removed, a special locator is used to select the correct upper and lower stops, and then the new ACL is reconstructed by drilling a bone channel (simply put, drilling a hole in the bone) and fixing the new ligament with internal fixation screws, etc. It looks like it was done in just a few words, as if it was very simple. In reality, the surgical notes are much longer than this. Because it is easy to understand, all the parts that involve technical expertise are ignored, and there is no mention of how to do it, just a description of the general meaning, so it makes a very difficult and complicated operation look easy. This is probably a bit like a book review, where one says “the cold comes and goes, and ten years have passed”, but in fact how much hardship and complexity has been passed by. Take the selection of the ligament stopping point, it can be said that the loss of a hair, a thousand miles, the position of a little bit in front or back, the ligament may be too loose or too tight to affect the function!