Knee ringing and then severe pain, may be related to the following diseases: 1, there may be internal knee injuries, such as anterior and posterior cruciate ligament rupture, or meniscus injury, or cartilage damage. Among them, ligament rupture is the most common, for example, when there is anterior cruciate ligament rupture, the patient is often due to the sharp straightening of the knee joint in the process, the foot or the calf is blocked. At this point, the ACL is overstretched, which then causes the rupture. The patient will often feel or even hear the ringing inside the knee joint, and will be accompanied by severe pain afterward. 2, there may be intra-articular free body, the so-called intra-articular free body, refers to the shedding of debris inside the joints, and gradually formed a hard object similar to the pearl and so on. When the patient moves the knee joint, it may block the activity of the knee joint, at this time it is possible to produce ringing, and accompanied by severe pain. 3, there may be a fracture around the knee joint, such as patella fracture, it is prone to this situation.