Inclusion Criteria:  Patients intending to undergo single-knee ACL reconstruction at our Institute of Sports Medicine. The age of 18 ~ 50 years old at the time of operation. Both men and women. BMI < 24. Complete or partial meniscectomy was performed at the same time as ACL reconstruction. Patients willing to undergo a second arthroscopic exploration 2 years postoperatively and to take the portal screws used to fix the ligaments during the initial surgery. Patients with preserved meniscus video during ACL reconstruction. The degree of knee osteoarthritis (KOA) at the time of operation was < Ⅲ of Kellgren Laurence level.  Exclusion Criteria:  Patients with severe knee cartilage injury. Patients with KOA≥KLⅢ at the time of operation. The patients cannot be followed up. Patients who refused the second arthroscopy and the removal of the internal fixation portal screw at the time of surgery. Patients with rheumatoid arthritis or other arthritis. Patients with other systemic diseases who take oral anti-inflammatory analgesics for years. Patients with multiple injections of drugs in the joint due to various reasons.