Meniscal injury of the knee: Meniscal injury is one of the most important causes of persistent knee pain after trauma. Younger meniscal injuries tend to have a history of significant trauma, while older patients with degenerative injuries may have no history of injury. The diagnosis of meniscal injury can be made by MRI, but the diagnosis can be confirmed by arthroscopy. The diagnosis or suspicion of meniscus injury requires arthroscopy and treatment. Depending on the type and extent of the meniscal injury, the decision is whether to repair the meniscus with sutures or to perform partial meniscectomy. Indications for meniscal suture: Acute meniscal injuries in young people with longitudinal tears near the edges and good knee stability are suitable for suturing. In contrast, the principle of partial meniscectomy is to remove the medial edge of the meniscus rupture and preserve the stable peripheral portion of the meniscus. Anterior cruciate ligament injury: The anterior cruciate ligament is an important structure for maintaining knee stability and should be surgically reconstructed in a timely manner after injury to avoid early degeneration of the knee joint. ACL injuries are common in young people with a history of knee injury. In the acute phase, there is knee swelling, pain, blood accumulation and dysfunction, and after the acute phase symptoms improve, there is knee pain, joint instability and easy sprain in sports. If there is interlocking and popping of the knee joint, it may be combined with meniscal injury. MRI examination can show anterior fork ligament injury with an accuracy rate of up to 90%. Arthroscopy can confirm the diagnosis under direct vision. Arthroscopic ACL reconstruction is the main method to stabilize the knee joint. It has the advantages of less trauma, faster recovery, and better efficacy. Patients with symptoms of knee instability are recommended to have reconstruction within six months after the injury to avoid secondary cartilage injury and meniscal injury. Commonly used reconstruction methods include autologous bone-patellar tendon (middle 1/3)-bone complex graft and autologous quadriceps tendon and thin femoral tendon to reconstruct the ACL, and allogeneic tendons and artificial ligaments can also be used to reconstruct the ACL. Anterior cruciate ligament reconstruction techniques are demanding, and both tibial and femoral tunnels must be accurately positioned, the ligament must be firmly fixed, the strength of the reconstructed ligament must be sufficient, and the rehabilitation exercises must be correct in order to achieve good results. Posterior cruciate ligament injury: The posterior cruciate ligament is the main structure that prevents the tibia from moving backwards and, like the anterior cruciate ligament, is an important structure in maintaining the stability of the knee joint. The posterior cruciate ligament is stronger than the anterior cruciate ligament, so patients usually have a history of more severe trauma. In the acute phase there is knee swelling, pain, blood accumulation and dysfunction, and after the acute phase symptoms improve there is knee pain, joint instability and easy sprain. If there is interlocking and popping of the knee joint, it may be combined with meniscal injury. In some patients with simple PCL injury, the symptoms can be basically relieved after treatment in the acute stage, and walking is normal, and the joint is painless when walking, but the patient generally feels the knee joint instability and cannot perform strenuous exercise. On local examination, there is knee swelling in the acute stage, and there is pressure pain and bruising in the N fossa. In the chronic phase, there is no swelling and pain in most cases, but there is thigh muscle atrophy, joint instability, and posterior fall of the upper tibia at 90° of knee flexion are important signs for the diagnosis of posterior cruciate ligament injury. MRI can show the extent of posterior cruciate ligament injury and identify whether it is a complete or partial injury. Arthroscopy can confirm the diagnosis under direct visualization. Acute simple posterior cruciate ligament injuries, especially partial injuries, may be considered first for non-surgical treatment. Immobilization in a cast at 30° of flexion for 3 weeks, partial weight-bearing walking with double crutches, and isometric contraction exercises for the quadriceps muscle; protection with braces for another 3 weeks, allowing movement at 0° to 60°, and straight leg raising exercises to strengthen the quadriceps muscle to reduce posterior tibial drop. Arthroscopic posterior cruciate ligament reconstruction is required for posterior instability of the knee. In combination with posterior posterolateral structural injury, early posterior cruciate ligament reconstruction and posterior posterolateral structural reconstruction are required. Commonly used reconstruction methods include autologous bone-patellar tendon (middle 1/3)-bone complex graft and autologous quadruple femoral semitendinosus tendon and thin femoral tendon to reconstruct the posterior cruciate ligament. Allogeneic tendons and artificial ligaments are also used for reconstruction. Due to the obstruction of the anterior fork ligament, reconstruction of the posterior fork ligament requires high surgical skills, and tibial tunnel drilling can easily damage the N fossa vascular nerve. Physicians who are not skilled in arthroscopic surgery should carefully consider whether to refer to a higher level hospital for treatment. Lateral collateral ligament injuries: The lateral collateral ligaments include the medial collateral ligament and the lateral collateral ligament, and simple lateral collateral ligament injuries are rare because of the toughness and strength of the iliotibial bundle on the outside of the knee. Injuries to the medial collateral ligament are relatively common. Patients usually have a history of significant trauma and present with pain and bruising in the area of the medial/lateral collateral ligament of the knee after the injury. Asymmetric opening of the medial joint space on external rotation stress test at 0° extension and 30° flexion suggests medial collateral ligament injury; asymmetric opening of the lateral joint space on internal rotation stress test at 0° extension and 30° flexion suggests lateral collateral ligament injury. Medial collateral ligament injury often combines with anterior cruciate ligament and medial meniscus injury, and lateral collateral ligament injury often combines with posterior cruciate ligament and posterior lateral structure injury, so pay attention to the examination to avoid missing. 1.X-ray orthopantomographs can show asymmetric opening of the medial or lateral joint space, and MRI examination can indicate the location and extent of injury and whether other ligament injuries are combined. 2.Simple partial tears of the collateral ligament can be treated conservatively with good results. After fixation with plaster or brace in straight position for 2~3 weeks, remove the fixation for non-weight-bearing activities of the joint, and after 6 weeks, the joint has no obvious pain and can gradually walk with weight. 3, simple complete tear of the medial collateral ligament whether the injury as soon as possible after the suture, there is still a debate. Some doctors believe that it should be sutured as soon as possible, but some doctors believe that conservative treatment also works well. Combined anterior fork ligament injury can be repaired and reconstructed medial collateral ligament and anterior cruciate ligament in one phase, or the anterior cruciate ligament can be reconstructed after conservative treatment of the medial collateral ligament. 4, simple complete tear of the lateral collateral ligament is rare, most combined with posterior cruciate ligament injury and posterior lateral structure injury, then to reconstruct the posterior cruciate ligament and posterior lateral structure in one phase.