(i) Overview Arthroscopy was initially applied only to the knee joint, mainly as an auxiliary means of examination. With the development of arthroscopic instruments, surgeons gradually began to perform simple knee arthroscopic procedures, such as meniscectomy, synovectomy, and free body removal. Knee arthroscopy has improved dramatically over the past 20 years, and the variety of knee disorders that can be treated through arthroscopy has increased significantly. Meniscal injuries alone can now be treated with partial meniscectomy, complete meniscectomy, suturing, and transplantation. The treatment of cartilage injuries has also evolved from repairing uneven cartilage surfaces to drilling, microfracture, and autologous chondrocyte transplantation. The change from traditional incision surgery to arthroscopic surgery for cruciate ligament injuries has significantly reduced the surgical trauma, made the surgery simpler and easier to perform, the intraoperative positioning is more accurate, and the patients recover quickly after the surgery, with a good therapeutic effect. At present, knee arthroscopy is not popularized enough in China and needs to be further promoted. (II) Indications Arthroscopy can be used to diagnose and treat a variety of knee joint disorders; for example, meniscus injury, anterior and posterior cruciate ligament rupture, articular cartilage injury, intra-articular free body (also known as joint rats), osteoarthritis, and various chronic synovitis. Patients should go to the hospital in a timely manner whenever symptoms such as swelling, pain, instability or strangulation occur in the knee joint due to sports injuries. Through the doctor’s examination and X-ray, MRI and other auxiliary examination to clarify the type of injury. If it is meniscus injury, cruciate ligament injury or intra-articular free body, it should be treated with arthroscopic surgery 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. （Contraindications Systemic or localized infectious diseases, such as fever caused by infection, boils on the skin near the knee joint. Severe high blood pressure, heart disease, diabetes, or other serious illnesses where the patient cannot tolerate anesthesia and surgery. (iv) Surgical Procedure After anesthesia is administered, the patient lies on his/her back on the operating table, which is strictly sterilized. A tourniquet is used at the root of the thigh to block the blood flow to the lower limb and reduce bleeding during surgery. Usually, three small incisions of 1 cm in length are made at the front of the knee joint, one of which is inserted into the entry tube to continuously inject sterile saline into the knee joint to inflate the joint cavity and facilitate the surgical operation; it is also able to reduce bleeding. One of the other two incisions is used to insert the arthroscope’s camera, which takes real-time pictures and displays them on a monitor so that the surgeon can see what’s going on in the joint by looking at the monitor images. The other incision allows the insertion of a variety of arthroscopic surgical instruments to perform various surgical operations. For example, the probe hook is used to investigate the structures in the joint for damage, the electric planer is used to remove the diseased synovial membrane, the basket forceps is used to remove the damaged meniscus, the grasping forceps are used to remove the free body, and the special positioner is used to assist in the reconstruction of the cruciate ligaments, and so on. 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 bandaged with cotton pads under pressure to minimize swelling of the joint and limb. The sutures are removed 1 week after surgery, leaving only 3 small 1 cm scars. (v) Complications As with any surgery, there are some complications associated with knee arthroscopy. For example, postoperative infection, neurovascular injury at the back of the knee joint, joint adhesion, and deep vein thrombosis of 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 take the initiative to move the ankle to promote blood return. On the second day after the operation, the patient can practice the muscle strength of the lower limbs and 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 from hospital in about 3-4 days; cruciate ligament reconstruction surgery and synovectomy surgery usually require hospitalization for 7-10 days due to more complicated postoperative rehabilitation. (VII) Results Compared with the traditional knee osteotomy, arthroscopic surgery is highly accurate, less traumatic, less painful, quicker recovery and excellent results. (viii) Other precautions Before surgery, it is important to avoid mosquito bites and boils on the skin near the knee joint. After the operation, you should pay attention to rest, follow the doctor’s instructions, and carry out rehabilitation exercises on time and according to the schedule.