(I) Overview Arthroscopy was initially applied only to the knee joint, mainly as an adjunctive means of examination. With the development of arthroscopic instruments, physicians gradually began to perform simple arthroscopic knee procedures such as meniscectomy, synovectomy, and free body removal. Over the past 20 years, knee arthroscopy has advanced tremendously and the number of knee disorders that can be treated through arthroscopy has increased significantly. Meniscal injuries alone are now treated with a variety of surgical procedures such as partial and complete meniscectomy, suturing, and transplantation. Treatment of cartilage injuries has also evolved from the initial revision of uneven cartilage surfaces to drilling, microfracture, and autologous chondrocyte transplantation. The change from traditional incisional surgery to arthroscopic surgery for cruciate ligament injuries has significantly reduced surgical trauma, made the surgery easier and more precise in positioning, and resulted in faster recovery and better outcomes. At present, arthroscopic knee technology is not popular in China and needs to be further promoted. (B) Indications Arthroscopy can be used to diagnose and treat a variety of knee disorders, such as meniscal injury, anterior and posterior cruciate ligament rupture, articular cartilage injury, intra-articular free bodies (also called joint rats), osteoarthritis, and various chronic synovitis. Patients should go to the hospital promptly when they have symptoms such as swelling, pain, instability or strangulation in the knee joint due to sports injuries. The type of injury should be clarified by the doctor’s examination and auxiliary examinations such as X-ray and MRI. If it is meniscal injury, cruciate ligament injury or intra-articular free body, arthroscopic surgery should be performed as early as possible. Chronic synovitis, early osteoarthritis and other diseases that are ineffective with conservative treatment can also be further diagnosed and treated by arthroscopy. (iii) Contraindications Systemic or local infectious diseases, such as fever caused by infection, long boils on the skin near the knee joint. Severe hypertension, heart disease, diabetes, or other serious illnesses where the patient cannot tolerate anesthesia and surgery. (iv) Surgical procedure After the administration of anesthesia, the patient is placed on the operating table on his back, and after strict sterilization, the surgery is ready to begin. A tourniquet is used to block the blood flow to the lower extremity at the root of the thigh during surgery to reduce bleeding during surgery. Three small 1 cm incisions are usually made in the anterior part of the knee joint. One of them inserts an inlet tube to inject sterile saline into the knee joint continuously to swell the joint cavity and facilitate the surgical operation; at the same time, it can reduce bleeding. The other two incisions insert an arthroscopic camera, which displays the real-time images on a monitor so that the surgeon can see what is going on inside the joint by viewing the monitor screen. The other incision allows for the insertion of various arthroscopic instruments to perform various surgical operations. For example, a probing hook is used to explore the structures in the joint for damage, an electric planer is used to remove the diseased synovium, a basket clamp is used to remove the damaged meniscus, a grasping clamp is used to remove the free body, and a special positioner is used to assist in the reconstruction of the cruciate ligament. The surgery is usually completed within 1 1/2 hours. After the surgery is completed, 3 small incisions are sutured and the lower limb is wrapped with cotton pads under pressure to reduce swelling of the joint and limb. The sutures are removed 1 week after surgery, leaving only 3 small scars of 1 cm. (v) Complications As with any surgery, there are some complications associated with knee arthroscopy. Examples include postoperative infection, neurovascular injury to the posterior knee, joint adhesions, and deep vein thrombosis in the lower extremity. However, the overall incidence is very low. (vi) Rehabilitation On the day after surgery, the affected limb is slightly elevated and the patient should actively move the ankle to promote blood return. On the second day after surgery, the patient can perform muscle strength exercises of the lower limbs and can walk on the ground. Depending on the condition, the affected limb can be fully weight-bearing, partially weight-bearing or non-weight-bearing when walking. Meniscectomy and free body removal surgery can be discharged in about 3-4 days; cruciate ligament reconstruction surgery and synovectomy surgery usually require 7-10 days of hospitalization due to more complicated postoperative rehabilitation. (vii) Effect Compared with traditional knee arthrocentesis, arthroscopic surgery is highly accurate, less traumatic, less painful, faster recovery, and excellent results. (H) Other precautions Before surgery, pay attention to avoid mosquito and insect bites on the skin near the knee joint to avoid skin boils and swelling. After surgery, pay attention to rest, follow the doctor’s instructions, and perform rehabilitation exercises on time and according to schedule.