Common Knee Injuries The knee joint is one of the most vulnerable joints in the body and is composed of the distal femur, proximal tibia and patella. The ligaments, capsule and meniscus that attach to them form the stable structure of the joint. The anterior cruciate ligament begins at the medial aspect of the femoral epicondyle and ends at the anterolateral aspect of the medial tibial tuberosity, limiting the anterior displacement and rotation of the tibia. The posterior cruciate ligament begins on the lateral aspect of the medial femoral condyle and ends at the posterior edge of the tibial plateau, just below the level of the joint, limiting the posterior displacement of the tibia. They are important intra-articular structures that maintain the stability of the knee joint. The meniscus, or semilunar cartilage, is a C-shaped disc of fibrocartilage within the knee joint that absorbs impingement, increases joint surface adaptation, increases joint stability, and helps to distribute joint fluid evenly. Arthroscopic Surgery With the advancement of science, society, and medical technology, significant progress has been made in the treatment of injuries to important structures within the knee joint by means of arthroscopic surgery. The excision, suturing and disc cartilage molding of knee meniscus or disc cartilage injury, repair or reconstruction of cruciate ligament injury, and release of the lateral support band and tightening of the medial support band for patellofemoral joint lesions caused by patellar dislocation or subluxation can all be successfully accomplished through arthroscopic surgery. Anterior cruciate ligament injuries Knee injuries are commonly associated with contact or non-contact injuries during sports. For ACL injuries, non-contact injuries mainly occur during sharp stops, turns, decelerations, jumps, and unstable landings, with the injury mechanism of joint valgus, external rotation, and hyperextension. And contact injuries often occur with multiple ligament injuries. The most common sports are basketball, soccer, badminton, and skiing. The injury is often followed by joint swelling, pain, misalignment, unstable walking, decreased athletic level, and many single knee sports movements that are afraid to do, or prone to re-injury. In addition, the repeated misalignment of the joint puts the meniscus and articular cartilage at high risk of injury. For patients whose conservative treatment is ineffective, surgery is necessary to restore normal joint function and motion level. The surgical technique has evolved through continuous progress from the previous ineffective simple repair to the current arthroscopic ligament reconstruction surgery. The graft can be reconstructed by choosing autologous bone-bin tendon-bone, autologous four-strand semitendinosus and thin femoral muscle, and allogeneic tendon. Different options are available for different requirements and conditions. Posterior cruciate ligament injuries Posterior cruciate ligament injuries are less common than anterior cruciate ligament injuries. Injury alone presents as a posterior sinking of the tibia, as in a motorcycle accident where the fender strikes the proximal front of the calf directly. Clinical symptoms are mild and easily missed. Most simple posterior cruciate ligament injuries are recommended for conservative treatment. Some physicians also recommend posterior cruciate ligament reconstruction for simple acute posterior cruciate ligament injuries with proven posterior instability greater than 15 mm. If the quadriceps is well developed and strong, it can usually compensate for the posterior cruciate ligament function and the athlete can continue to play sports. After rehabilitation, patients who still have symptoms of posterior cruciate ligament injury instability will require reconstructive surgery. The surgery is more difficult than ACL reconstruction and the results are less predictable. Currently, the commonly used graft is bone-tendon-bone. Allograft patellar ligament or Achilles tendon can also be chosen. Double-bundle reconstruction is more consistent with the anatomical features of the posterior cruciate ligament. Arthroscopic surgery for simultaneous reconstruction of anterior and posterior cruciate ligaments In addition to the relatively important anterior and posterior cruciate ligaments, there are many other important structures in the knee joint: such as the medial collateral ligament, the posterior lateral complex, and severe injuries often involve injuries to multiple ligaments. For injuries to multiple ligaments, as well as dislocations of the knee joint, which are serious injuries, timely surgery should be performed to simultaneously reconstruct multiple ligaments that affect the stability of the knee joint. The treatment is more complex and requires greater surgical precision. Meniscal injuries Meniscal injuries are the most common lesions for arthroscopic knee surgery. The medial meniscus is more likely to be injured because the medial meniscus is closely attached to the joint capsule, while the lateral meniscus has a free zone. Meniscal injuries are rare in children and can be seen in adolescents, with a peak incidence in the thirties and forties. After the age of fifty, meniscal injuries are more often due to osteoarthritic factors. Meniscal injuries are characterized by pain in the joint space, snagging sensation, popping and interlocking. The types of meniscal injuries include incomplete tears, barrel stem tears, flap tears, radial tears, and compound tears. Stable meniscal injuries that are asymptomatic may be treated conservatively. Meniscal injuries that cause persistent symptoms require arthroscopic surgical treatment. Currently, meniscus is treated by excision of the tear site or meniscal suturing whenever possible. The inner 2/3 of the meniscus has no blood flow and usually needs to be removed at the time of injury. In adults, there is blood flow in the outer 1/3 of the meniscus and tears in this area often heal spontaneously if they are less than 15 mm. Larger tears require suturing. Meniscal suturing techniques include inside-out sutures, outside-in sutures, total intra-articular sutures, or incisional sutures. In recent years, the use of absorbable staples in meniscal repair has led to the widespread adoption of the total intra-articular suture technique. Unfortunately, however, there have been reports of detachment of absorbable staples, and biomechanical studies have shown that the fixation strength of this method is inferior to that of suture fixation. Incisional sutures are frequently employed for tears in the marginal region of the meniscus. Sutureable meniscal injuries often coexist with ACL injuries, and reconstruction of the ACL to restore joint stability can protect the sutured meniscus, which has a much higher success rate than an unstable joint. In patients with meniscectomy and some early osteoarthritis, meniscal transplantation may be used. Short-term follow-up results show satisfaction in 2/3 of patients. In the future, bioprosthesis technology will make regeneration after meniscectomy possible. Discoid cartilage injury The discoid meniscus, also known as discoid cartilage, generally develops in children and adolescents. This is when the meniscus loses its normal structure, thickens in a discoid shape, and is easily damaged. There are three types of disc meniscus: complete, incomplete, and overactive (ligamentous). The main manifestations are bouncing and popping of the knee joint and limited knee extension. The main treatment is meniscectomy, and for the overactive type, excision may be required if the tear is severe. There are three main surgical treatments for disc cartilage: disc cartilage molding, partial resection, and total resection of the disc cartilage. If the tear can be repaired then a molding with sutures is used.