The patient accidentally sprained his left knee playing soccer, and at the moment of sprain, he heard a “pop” sound in the joint, followed by joint pain, swelling, difficulty in continuing activities, and difficulty in walking. After a few weeks of treatment, the knee symptoms improved, but the patient was still afraid to run and often felt instability and weakness in the knee joint when walking fast, often with soreness and slight swelling. The patient came to our clinic for further treatment. In the outpatient clinic, the patient’s knee was examined and found to be unstable, with a positive Lachman test and anterior drawer test. The patient was hospitalized and underwent “arthroscopic reconstruction of the left knee ACL rupture” in the operating room. The left knee X-ray was taken after the operation as follows: the affected limb was fixed with a brace, functional exercises were guided, and the left knee recovered well after regular outpatient review as follows.