Zhu, 76, has been suffering from osteoarthritis in her knee for more than 10 years. Several years ago, her doctor recommended that she undergo total knee replacement surgery, but due to her fear of surgery, she was unable to make up her mind. However, after carefully studying the knee film, the doctor found that her joint lesion was limited and she was eligible for the relatively less damaging “unicondylar knee replacement surgery”. Zhu was confused by this new term, what does unicondylar replacement mean? It turns out that our knee joint can be divided into three relatively independent parts based on anatomy and function – the medial compartment, the lateral compartment and the patellofemoral compartment. In middle-aged and elderly people, the destruction of these three compartments due to osteoarthritic joint degeneration, or “bone spurs” as they are commonly called, causes knee pain, which often requires an artificial knee replacement when it is in an advanced stage. Statistics show that in about one in ten cases of artificial knee replacement, the lesion is limited to one compartment, with the medial compartment being the most common. In the past, due to technical limitations, even unicompartmental lesions had to be replaced with all three compartments together, which is often referred to as total knee replacement (see Figure 1), which is like treating appendicitis as intestinal cancer. To solve this problem, unicondylar replacement technology was created. A unicondylar replacement, also called a partial replacement (see Figure 2), preserves the normal joint surface of the knee and replaces only the diseased compartment, thus offering the advantages of less injury, less pain, and faster recovery. In addition, unicondylar replacement, unlike total knee replacement, does not require the removal of the anterior and posterior cruciate ligaments and the healthy meniscus, preserving the balance and proprioception of the knee joint, and bringing the postoperative function of the joint closer to its normal physiological state. In conclusion, unicondylar replacement provides a cost-effective treatment option for patients with advanced joint disease by improving joint function with less damage. Of course, the choice of this procedure must be evaluated by an experienced joint surgeon. Only those medial and lateral compartment lesions that are not severely deformed are the best indications for unicondylar replacement, otherwise total knee replacement is the safest option.