One day, a beautiful young girl came to the outpatient clinic. Xiao Liu, a senior in college, had fallen on her right knee 3 years ago, causing swelling and pain, which was relieved after 2 months of rest, but after that she always felt that her right knee was too weak to go up and down stairs, and she could not run fast enough, and even if she ran, she could not stop at once. At first, my parents thought I was a girl, so I might be a little delicate, mistakenly thinking that I would be fine if I rested and rested, so I didn’t care too much. Three years have passed, the symptoms have recently become more obvious, wearing a skirt in the summer, a closer look will find the right leg than the opposite side of a thin circle, which attracted the attention of parents. Parents took to several hospitals, but none could give a clear diagnosis. Xiao Liu, who was about to graduate from college, became concerned about her knee joint and wanted to go on a hiking trip with her classmates before joining the workforce, but she was not able to go due to knee weakness in case of an accident. The stability of the knee joint requires the internal strong cruciate ligament to be intact. It is hidden deep inside the knee joint and cannot be seen or felt. Once a particular one ruptures, knee instability occurs, sometimes not very typical, and the pain is often overlooked as the swelling in the joint subsides after a period of rest and pain is not severe after the injury. However, the prominent manifestation is that the affected leg can’t eat the force when going up or down the stairs, and needs to hold the wall when going up or walk with the body inclined. When running, the affected leg does not dare to make a sudden effort, and when running, the affected leg does not dare to stop sharply, and there is a fear of knee movement. Xiao Liu had this problem. On examination, the right knee posterior drawer test was positive, the knee joint was posteriorly unstable, the right knee upper thigh diameter was 37.5px shorter than the opposite side, and MRI showed posterior cruciate ligament injury in the right knee. After admission, knee arthroscopy was performed to confirm that the posterior cruciate ligament of the right knee was ruptured, with less than 1/4 fibers remaining and poor elasticity, and was unable to perform posterior cruciate ligament function, and minimally invasive posterior cruciate ligament reconstruction was performed. After the surgery, he was protected by a brace and resumed normal daily life after 3 months, and since then, he has not been afraid to go up and down the stairs. Mr. Li, a 35-year-old IT elite, had fallen down the stairs 5 years ago and suffered from left knee weakness, and sprained again this year, with swelling and pain in his left knee and limited movement. After admission to the hospital, arthroscopy revealed that the anterior cruciate ligament of the left knee had been absorbed and the tibial stop had completely disappeared. Magnetic resonance imaging (MRI) of the anterior cruciate ligament showed poorly, as shown by the arrow in the figure. He was treated with an arthroscopic minimally invasive ACL reconstruction and returned to normal work after 3 months, and the knee instability disappeared. Young patients with recurrent knee cruciate ligament injuries come to the doctor reminding me that I may need to educate myself about this. In young people, if you have chronic weakness after a knee sprain or fall, an inability to run fast, and a sense of fear in the knee going up and down stairs, be alert to possible internal knee ligament damage that needs prompt treatment to avoid muscle atrophy and further knee degeneration leading to a loss of quality of life. It is imperative that you seek professional medical help at this time.