I. Concept The appearance of popping in the knee joint is often a mechanical disorder due to congenital, developmental, injurious, degenerative, or neoplastic lesions of certain tissues in the joint. The source, location, loudness, frequency and accompanying symptoms are characteristic of different diseases. There are many knee joint diseases that can cause knee ringing, including meniscal injury, intra-articular free bodies, cartilage lesions, synovial lesions, etc. The ringing has its own characteristics, and it is relatively easy to identify the source of ringing and diagnose meniscal injury, discoid meniscus, osteoarthritis, while synovial crease syndrome and intra-articular ligament injury are difficult to be clarified by physical examination and can be easily confused with meniscal injury. They can be easily confused with meniscal injuries. The knee can be clinically affected by congenital abnormalities or acquired lesions of the tendons and ligaments surrounding the knee joint. A patient with painless popping in the knee was diagnosed with meniscal injury and underwent knee arthroscopy, but no abnormalities of the meniscus or other intra-articular structures were seen during surgery. This suggests that abnormalities of the iliotibial bundle can also lead to knee motion disorders. In addition, biceps femoris tendon, semitendinosus, semimembranosus, and popliteal tendon popping is rare, but has been reported. We believe that knee popping is a mechanical disorder that occurs during joint motion due to various pathological factors within or around the joint, and the presence of popping has important clinical significance. There are many causes of knee rattling, and meniscal-derived rattling is the most common, while synovial, cartilage, ligament, and periarticular tendon tissue lesions or anatomical abnormalities can all lead to rattling. Each disease has its own characteristics, and a comprehensive and accurate diagnosis can only be made by combining history, signs and imaging and arthroscopic dynamic observation. The analysis of the popping characteristics is useful for the differential diagnosis of knee disorders, as shown in Table 1. Treatment Simple joint popping is not painful and does not affect the body much, so no special treatment is needed. If the rattling occurs as a symptom of a knee disease, the primary cause should be treated. The origin of knee rattling is diverse, and meniscal rattling is the most common symptom, so knowledge of the characteristics of the rattling can help to make a correct diagnosis and avoid unnecessary surgical interventions.