A young man who underwent a double-bundle reconstruction of the ligament due to an ACL injury. At the 3-month postoperative review, the ligament signal was very good on MRI, and both the amount of fibers and ligament tension were very satisfactory; the joint stability was also very good. However, at the 6-month postoperative review, it was found that most of the ligament fibers had been absorbed, and the remaining small portion of fibers were obviously lax; the stability of the joint was obviously abnormal. The young man wondered why the ligaments that were good at 3 months postoperatively became so bad at 6 months postoperatively. Reviewing the young man’s rehabilitation training in the past 3 months, it was found that the young man ran more than 3 times the prescribed time and even started playing basketball in order to recover as early as possible. Finally, the doctor concluded that the over-eager workout caused the failure of the reconstructed ligaments. Why does aggressive training not get good results instead? To understand this question, one needs to understand the changes in the graft after ligament reconstruction. ACL reconstruction is to first make the tendon into a ligament-like structure, i.e. a graft, and then implant the graft into the joint, using the graft to connect the two lower limb bones – femur and tibia, thus reducing the misalignment between the two bones, i.e. restoring the stability of the joint. However, it does not mean that everything is fine after ligament reconstruction, because for the graft to function properly, there needs to be a reliable healing of the graft to the bone firstly, and secondly, its fibrous component needs to change from tendon fibers to reliable ligament fibers, which is a complex and more important process. When the graft is first implanted in the joint, necrosis can occur due to ischemia. In the early stages of ischemic necrosis, the collagen fibers of the graft have not disintegrated and the strength of the graft is still present; next there is disintegration of the collagen fibers of the graft, when the strength of the graft decreases; then the surrounding vessels grow in, the graft begins to vascularize, the collagen fibers begin to remodel, and the strength of the graft is gradually restored. The strength of the graft is lowest in the late stages of graft necrosis and early stages of vascularization. In humans, this period generally corresponds to 4, 5, and 6 months after surgery, and in individuals this period may be longer. Without stress stimulation, the tendon fibers of the graft will not become ligament fibers, but will become disorganized collagen fragments with very low strength and will not be able to function as a ligament. However, excessive stress stimulation can cause the weaker graft fibers to rupture during the shaping process. Therefore, special attention is given to the 4-6 months in the postoperative rehabilitation program, which is designed to both stress stimulate and protect the reconstructed ligaments. However, it is true that some patients are out of their depth or overzealous in this phase. Some show up as over-range training and starting sports programs too early; some do the prescribed program but are severely over-timed; and some simply show up with excessive daily walking, especially brisk walking. The end result is the same: the graft does not get through the shaping phase and fails. Therefore, in the 4-6 months after surgery, firstly, you should strictly follow the rehabilitation program and not go over the range; secondly, you should strictly follow the rehabilitation time and not go over the amount; in addition, do not walk too fast for a long time. In order to protect the ligaments during the ligament shaping phase, an anterior cruciate ligament injury brace is recommended in Europe and the United States. This brace is specially designed to prevent excessive stress on the reconstructed ACL by applying resistance as the knee joint approaches extension; it protects the reconstructed ligament while ensuring completion of the rehabilitation program and even more aggressive rehabilitation. The brace is suitable for patients who need to perform an excessive amount and range of motion, i.e., who want to exercise as early as possible, as well as for patients who need to walk for long periods of time and too fast in their daily lives. In recent years, this type of brace has been introduced to China (for example, DJO brand in the United States), but because it needs to be customized according to the patient’s leg shape, which is slightly troublesome and expensive (about 3000 RMB), it is currently used only by some athletes and has not yet become a popular product. Finally, I would like to remind all patients that the purpose of ligament reconstruction is to use the ligament for the rest of your life, so don’t let your love of sports and haste cause the ligament to fail and eventually make you unable to play sports. Although it is possible to have a ligament revision surgery later, it will take more time, money and effort. Or learn from Europe and America and spend some money on a foreign device (ACL protection brace) for a few months. Of course, there are other possible causes of deterioration after ACL reconstruction, such as joint infection, poor collagen fiber formation, etc., but improper exercise is really the main cause and needs extra attention.