When the leg is bent, there is a ringing sound in the knee joint, which may be degenerative osteoarthritis, or free body of the knee joint, and the meniscus damage of the knee joint may also appear the phenomenon of joint ringing. You can go to the orthopedic department of the hospital to find a doctor’s interview, the doctor combined with the preliminary analysis of the examination. If it is degenerative osteoarthritis of the knee joint or free body of the knee joint, you can improve the X-ray examination of the knee joint to determine the condition. If it is a meniscus injury of the knee joint, you can improve the magnetic resonance examination of the knee joint to determine the condition. According to the results of the examination and then do the appropriate treatment. For degenerative osteoarthritis, sodium vitrate can be injected into the joint cavity. For knee joint free body or more serious meniscus injury can consider arthroscopic repair or removal of free body and other treatments. Usually avoid excessive flexion and strenuous exercise to help the knee joint health.