ACL injury is a common orthopedic disorder, after the injury is often manifested as instability of the knee joint, and often combined with other structures in the knee joint: meniscus, femoral condyle and medial and lateral collateral ligament injury, seriously affecting the life and work of patients. there are more reconstruction methods for ACL injury, and arthroscopic ACL reconstruction is currently one of the best methods for the treatment of ACL injury, since June 2005 to June 2008 From June 2005 to June 2008, 26 patients with ACL injury were reconstructed by arthroscopic reconstruction of the four N cord tendons, which are reported as follows: 1. Materials and methods 1.1 General information In this group of 26 cases, there were 18 male and 8 female cases. The age was 19-62 years old, with an average of 29 years old. There were 17 cases of left knee and 9 cases of right knee. Causes of injury: sports injury in 12 cases, vehicle injury in 6 cases, fall injury in 4 cases, and fall injury in 4 cases. Post-injury to surgery: 3 days-7 years, average duration of disease before surgery 8.9 months. Preoperative radiographs and MRI were performed, and MRI reported the diagnosis of injury or fracture in 22 cases, with 4 cases with unclear display. There were 6 cases of combined medial meniscus injury, 11 cases of lateral meniscus injury, and 4 cases of both medial and lateral meniscus injury. There were 8 cases of combined medial and lateral collateral ligament injury, and 1 case of posterior cruciate ligament injury. Intraoperative meniscus suture was performed in 8 cases, and the rest underwent partial or total meniscectomy. The medial and lateral collateral ligaments were repaired. Intercondylar fossa molding was performed in all cases. Preoperative physical examination showed swelling of the knee joint in 15 cases, positive floating patella test in 9 cases, positive lateral knee stress test in 8 cases, positive anterior drawer test in 19 cases, positive Lachman test in 22 cases, positive axial shift test in 16 cases, and interlocked knee joint in 5 cases. All cases were scored by Lysholm before and after surgery. 1.2 The procedure was performed under combined rigid and lumbar anesthesia, with the affected limb in the supine truncal position and an electric tourniquet placed on a special leg brace at the root of the thigh. In patients with definite ACL injury requiring reconstruction, the arthroscope is first withdrawn and a small incision of approximately 4 cm in length is made 1 cm medial to the tibial tuberosity to reveal the tendinous portion of the semitendinosus and thin femoral muscles, and the tendon is taken from the tendon apparatus and folded into four strands approximately 11 cm long and closed in the middle with 2-0 antimicrobial Vecchio sutures. The two ends were sutured with No. 5 Aegis non-absorbable sutures, and the sutures were retained at both ends. The circumference of the N cord tendon was measured after suturing and pre-tensioned for backup. The arthroscope was reinserted, and the infrapatellar crease and ACL remnants were removed with an electric planer, and intercondylar fossa shaping was routinely performed to prevent its impingement on the implant. The attachment point of the reconstructed ACL femur was positioned at the top of the intercondylar fossa at 10.5 (right knee) or 1.5 (left knee), with the outer wall of the intercondylar fossa approximately 5 mm from the posterior border of the bone cortex. tibial end tunnel preparation: the tibial guide was fixed in the 55° position. 1.3 Rehabilitation A functional brace was used for 8 weeks postoperatively. Isometric contraction of the quadriceps muscle, 0°-90° knee flexion and extension exercises and weight-bearing were started 1 week after surgery. At 2 weeks after surgery, 90° static squat, 6 weeks stationary bicycle exercise, 12 weeks isotonic exercise of 20°-130°, 6 months can be swimming, jogging, stair climbing and other strength recovery exercises, 12 months can resume strenuous exercise according to the situation. 1.4 Follow-up All patients obtained follow-up after surgery for six months to three years, with an average of 1.2 years, to check the stability of the knee joint, mobility and drawer test, using the Lysholm knee score [1], and comparing with the preoperative period. 2, Results There were no complications such as joint adhesion, wound infection, implant fracture, or vascular nerve injury in all cases. 12 cases had different degrees of joint effusion requiring treatment after surgery. 2 cases had different degrees of periprosthetic pain. 1 case had numbness of sensation in the anterior mid calf, which was relieved after 2 months with neurotrophic treatment. 1 case had a positive I° anterior drawer test of the knee, and all the remaining patients returned to their original motion or work. All the knee instability symptoms disappeared, the anterior drawer test was negative, and the knee flexion and extension ranged from 0 to 130°. The Lysholm score improved from 58 points before surgery to 95 points at the final follow-up, of which 18 cases were excellent (95-100), 6 cases were good (85-94), and 2 cases were moderate (65-84), with an excellent rate of 92.3%. 3. Discussion 3.1 ACL reconstruction indications ACL injury is more common in sports injuries, which can cause instability symptoms, but also secondary meniscal and cartilage damage, and eventually cause osteoarthritis of the knee. With the development of minimally invasive arthroscopic techniques, arthroscopic ACL reconstruction is considered to be the routine treatment for ACL rupture. The ACL consists of two parts, the anteromedial bundle and the posterior lateral bundle. The length and tension of the fibers of each bundle of the two ligaments vary with the extension and flexion of the knee joint. The anteromedial bundle remains tense in the flexed knee position and the posterior lateral bundle remains tense in the extended knee position, and injuries that are predominantly ruptured in the posterior lateral bundle are often associated with joint instability.