Auntie Wang is a hard-working housewife in her 60s, working all day for the family’s living, not only to bring up the children, but also to take care of the family’s acreage. She has been in pain for more than seven years, and when she moves around a little more, she starts to limp. Her knee pain has a characteristic, that is, only the inner side of the pain, the outer side does not hurt. Auntie Wang was referred to a local hospital’s sports medicine department for treatment. After a patient examination and reading of the films, the doctor said, “Your disease is called osteoarthritis of the knee, and the cartilage in the medial half is severely worn and needs to be replaced by an artificial joint surface, but the cartilage in the lateral half is still good and can continue to be used, after all it is better to have the original.” Auntie Wang was delighted to hear, “I used to hear people say that the whole knee had to be replaced, which scared me to sleep, but now I hear you say that half of it can be replaced, so I’m not afraid!” After careful preparation, the sports medicine team performed a knee “unicondylar replacement” for Auntie Wang, and the surgery went very well, and she walked more than 100 meters with her walker on the first day after the surgery. Auntie Wang said happily, “I didn’t expect to recover so quickly from the unicondylar replacement, and I can walk with strength and feel no pain, I should have known I wouldn’t have endured the pain for so long!” Diagram of unicondylar and total knee replacement: the left side is a unicondylar prosthesis, with less bone amputation and the anterior and posterior cruciate ligaments intact; the right side is a total knee prosthesis, with more bone amputation and the anterior and posterior cruciate ligaments removed. Osteoarthritis of the knee is a common disease among middle-aged and elderly people, with a prevalence rate of 8.1% in China and about 120 million people suffering from the disease nationwide. As we age, the cartilage in the knee joint gradually wears away, and when the surface cartilage wears out and a state of “bone grinding” occurs, the surface cartilage has to be replaced by surgical treatment. In recent years, with the advancement of medicine and the improvement of quality of life, people are paying more and more attention to the preservation of the motor function of the knee joint, and the concept of “knee preservation” has emerged, and the concept of “stepwise treatment” for knee osteoarthritis is gradually gaining popularity. In most cases, the cartilage in the medial and lateral knee joints wears out asynchronously, often the cartilage on one side is worn out while the other side is still in good condition, so it is not necessary to replace the entire knee joint, but only the cartilage on the damaged side. Unicondylar replacement is different from total knee replacement in that it is a “knee preservation” procedure that replaces only the surface of the knee joint on the side with severe cartilage wear, and leaves the ligaments intact, resulting in less trauma, faster recovery, better knee function, and higher patient satisfaction.