Do you know the least invasive and most effective way to treat these conditions when you feel something is constantly stuck in your knee, when you walk or run with regular weakness, when you have unexplained knee swelling and pain? That is arthroscopic examination and treatment surgery. As the name implies, an arthroscope is a set of lenses that reflect the condition of the joint. Arthroscopy has been widely used for more than 50 years since its initial invention. The arthroscopy system consists of a cold light source, fiber optic cable, lens, cable and monitor. The arthroscope lens is only 4 mm thick and contains a set of optical fibers and a set of lenses. The optical fibers transmit light into the joint, and the image inside the joint is transmitted through the lenses. Outside the joint, the optical fibers are connected to the cold light source through a fiber optic cable, and the lens is connected to the monitor through a cable with a photoelectric conversion device. With this system, the cold light illuminates the joint, and the monitor allows the physician to view the various tissue structures within the joint. The arthroscopy begins by dilating the joint cavity, and the lens is inserted into the knee joint along with a trocar that is cleverly designed to both inject water into the joint and drain the water out of the joint. During the arthroscopic procedure, a 6-8 mm skin incision is made in the joint and the arthroscopic lens with the cannula is inserted, and the joint cavity is filled with water by turning on the water injection switch. Then, through another incision of the same size, various delicate instruments are inserted into the joint and it is ready for undersea exploration. Arthroscopic examination and treatment procedures were first used in the knee joint, and the technique of knee arthroscopy is now very mature. This is followed by the shoulder joint, with tantalizing applications in the elbow, wrist, ankle and other small joints. One of the most interesting tasks in arthroscopy is catching arthroscopic rats. An arthroscopic rat is scientifically known as an intra-articular free body, which is generally a part of a joint that has been detached from various intra-articular structures during degeneration or injury, and can take various forms and have a hard texture. The intra-articular free body is highly mobile and can move around in various parts of the joint like a mouse, hence the name. The rat can become lodged in the joint space, causing sudden pain and inability to flex and extend the joint, which is called interlocking. Patients who frequently have joint locking should seek medical treatment. In the past, because arthroscopy was not available, an incision was required to remove the joint rats, but because of the mobility of the joint rats, arthrocentesis was somewhat blind and sometimes the entire joint had to be opened for one joint rat, just like tearing down an entire house to catch a mouse in it, and the damage was self-explanatory. With arthroscopy, this becomes a breeze. Once the arthroscope is inserted, there is nowhere for the arthroscopic rat to hide, and then a special clamp can be inserted through another small incision to catch the rat. In the knee, arthroscopy is most commonly used to treat meniscal injuries. In the medial and lateral joint spaces of the human knee, there is a gasket made up of fibrocartilage called the meniscus because of its crescent shape. The meniscus distributes stress, cushions shock, and increases the stability of the joint, thus reducing the wear and tear on the articular cartilage and slowing down the aging of the joint. Damage to the meniscus may occur during a sprain or other trauma to the knee joint. As we age, the meniscus also becomes brittle and can break under the constant stress of daily life. Not only does the damaged meniscus lose its function of protecting the joint, but it can cause joint pain, popping and joint interlocking, which then requires arthroscopic surgery. Under the arthroscope, the site and extent of the meniscus damage can be seen at a glance, and the meniscus can be repaired or removed in conjunction with the time of injury. The most valuable application of arthroscopy for the athletic person or athlete should be ACL reconstruction of the knee. Extension and flexion of the knee is accomplished by movement of the proximal platform of the lower leg (tibial plateau) around the arc of the distal thigh (femoral condyle). To prevent excessive forward or backward sliding of the plateau, two ligaments emanate from the femur and are anchored to the anterior and posterior edges of the tibial plateau like a chain. These two ligaments are called cruciate ligaments because they cross each other. The ACL is the ligament that goes to the anterior edge of the tibial plateau, and because it is the most important stabilizing structure of the knee, it often bears the brunt of injury in the event of trauma. Immediately after an ACL injury, there is joint pain and swelling, along with impaired knee extension and flexion. After rest, the swelling usually subsides and mobility is restored, but it often leaves chronic pain in the knee joint, and the joint feels unstable when walking, often weakens, or suddenly falls. Patients will not be able to run, which means they lose their athletic ability, and thus require surgery. The torn ACL is not strong enough to withstand normal stresses after suture repair, so it must be reconstructed, i.e., the torn ligament is replaced with a complete, ligament-like structure. These replacement structures are often taken from the patellar ligament at the front of the knee or the semitendinosus tendon at the posterior medial aspect of the knee. In the past, ACL reconstruction was a major undertaking that required opening the knee joint through one or two large surgical incisions, which was highly invasive and had poor postoperative results. Currently, the standard procedure for ACL reconstruction is performed arthroscopically, which is much less invasive and has significantly improved outcomes. Due to improved arthroscopic techniques and postoperative rehabilitation, most athletes who have had their “anchor chains” replaced are able to return to sports. Arthroscopy is a leader in the management of synovial disease. In the past, when a patient had unexplained joint swelling and pain, doctors often dismissed it as “synovitis” because it was difficult to identify the specific cause, and it was certainly difficult to find a definitive treatment. Under arthroscopy, the normal synovial membrane is yellowish-white in color and, except for some special areas where synovial folds are present, is generally spreading and does not protrude into the joint. When acute synovitis is present, the synovium becomes reddish from yellowish white and dense vascular shadows can be seen at close range. When there is a variety of chronic synovitis, protrusions of varying morphology form from the synovial wall into the joint cavity. In osteoarthritis, synovial protrusions resemble clumps of seaweed; in rheumatoid arthritis, synovial hyperplasia appears as short columns, papillae, or piles of grapes, and a vascular opacity may appear on the white articular cartilage surface; in villi-nodular synovitis, interlocking villi and nodules can be seen on the synovium; in gouty arthritis, small crystals of uric acid can be seen on the congested synovium -In synovial chondromatosis, not only dozens or hundreds of roaming mice can be found in the joint cavity, but also many mice can be seen in the synovium waiting to be born. By observing the synovial congestion and morphology, the doctor can have a general understanding of the disease and can take the corresponding lesions for pathological examination to make a clear diagnosis. Of course, arthroscopy also allows for direct removal of the diseased synovium, which significantly improves the targeting and efficiency of the doctor’s treatment. Arthroscopy is actually one of the endoscopic systems that are increasingly used today. Arthroscopic techniques are favored by doctors and patients because of their high reliability in the diagnosis of diseases, low damage in the treatment of diseases, high efficacy, and fast recovery of joint function after surgery. Arthroscopic surgery is a very important and promising branch of orthopedics. It is believed that with the further development, promotion and application of arthroscopic technology, more patients will be brought good news.