The role of cartilage in human joints is twofold: to reduce friction during joint movement and to cushion the load transmitted through the bone, which is equivalent to a cushion. Unlike many other tissues, cartilage is not vascularized. The cartilage in normal joints is hyaline cartilage, very polished, containing type II collagen, glycoproteins and a number of other microstructures whose composition changes with age. Bone tissue is repaired by bone healing after injury, and muscle tissue is repaired by scar attachment after injury. With proper treatment, muscle form and strength can be well restored. However, when the hyaline cartilage within the joint is damaged, it is not possible to repair it by the same type of cartilage, but by a type of tissue called fibrocartilage. This fibrocartilage is not as smooth or as strong as hyaline cartilage, and is prone to fracture or even shatter under external forces. In general, hyaline cartilage cells are lifelong cells and cannot be regenerated. For example, if you drive a car with a flat tire, a more convenient solution is to change a tire. However, what if there is no available spare tire? Then the only way is to press the wheel. Cartilage damage manifests itself in the same way as this car, because there is no homogeneous cartilage that can be adequately repaired. All the doctor can do is try to reduce the patient’s pain and improve the function of the joint. Knee cartilage is the most vulnerable cartilage, and treatment options include physical therapy, oral medications, injectable medications, and other more recent methods. However, all of these methods have certain drawbacks and short duration of action, and some even have significant side effects. Some drugs can cause cardiovascular and gastrointestinal adverse effects. If the arthritis is severe, the treatment is instead clear: it is a joint replacement. It’s like a house with a collapsed roof that needs a new roof. If the damage to the articular cartilage is severe enough to cause lasting direct bone-on-bone friction, joint replacement is required. The technology for knee replacement is well established, with both gender-specific and individualized artificial joints designed specifically for each individual. These gender-specific prosthetic joints are designed according to gender-specific anatomical features, have a thinner form, provide more natural patellofemoral mobility, and are particularly suitable for female patients. The individualized gender-specific prosthesis is an artificial joint designed with specialized computer software based on MRI or CT images of each patient’s knee joint. In this way, the surgeon provides not only a unique surgical experience, but also an artificial joint that is specifically best suited to each patient’s lifestyle. It’s like being tailored to fit at a tailor’s. Although knee replacements are relatively well established, there are still many potential complications, including infection, blood clots, loosening and even breakage of the artificial joint. Despite more thorough preoperative testing and appropriate medications, postoperative infection prevention, anticoagulation, and physical therapy, some complications do occur. If the arthritis is mild, many treatments can be used. Even drinking a cup of green tea and practicing yoga may help. If there is a small crack in the roof, there are many effective ways to treat it, including repairing the piece directly. For a moderate degree of cartilage damage is a bit more problematic to deal with. The arthritic lesion is less than the extent of an artificial joint replacement, but a simple repair would not be effective. Moreover, it may be a young patient. In this case, the surgeon tries to postpone the artificial joint replacement, which is like repairing a roof. Some of the more common methods used are injecting hyaluronic acid into the joint, or hormones, or performing a joint cleanout and drilling a subchondral hole to allow local bleeding to increase the chance of local repair. Sometimes, all of these approaches are tried and still have no effect, and, to use the roof analogy, it’s time to start leaking. Surgeons then revisit the root of the problem and try to discover ways to allow new hyaline cartilage to grow. What is commonly used is the use of mesenchymal stem cells, or the use of platelets to promote the aggregation of stem cells. These primitive MSCs are also present in the bone, and surgeons seek to find these cells, extract them, grow them and then inject them into the desired area. To date, each surgeon has used his or her own experience in treating cartilage injuries in the way that he or she is most familiar and appropriate, and it is difficult to really determine which approach is best for a particular patient. More basic and clinical trials are still needed to determine the exact efficacy of each approach. What works well for some patients may not necessarily work as well for others.