There are many reasons why knee joints may rattle during flexion and extension activities, and osteophytes are only one of the causes of knee joint rattle, but not the only one. Possible causes of knee ringing are: (1) Osteoarthritis of the knee joint: Osteoarthritis of the knee joint is most often seen in middle-aged and elderly people. It is characterized by pain, discomfort and swelling of the knee joint, and a popping sound in the knee joint during activity. x-ray films show varying degrees of osteophytes in the osteoarthritic area. (2) Meniscal injury of the knee: Meniscal injury is usually seen in young people with a history of trauma and strenuous exercise, pain, weakness, locking (the knee joint is stuck when flexed and extended to a certain angle) and popping. If the examiner fixes the affected thigh with one hand, rotates the lower leg and flexes and extends the knee at the same time, a popping sound and pain may occur. Severe meniscal injury or injury for a longer period of time can be seen as thigh muscle atrophy. (3) Patellar chondromalacia: Patellar chondromalacia is mostly seen in middle-aged and elderly people. When the knee joint flexion and extension activities with swelling, pain and joint ringing, symptoms are sometimes mild and sometimes heavy, the effect of various treatments are not very satisfactory. When the patella is rotated, the patellar surface can be felt to be uneven and there is a “rustling” sound when it rubs against the femoral condyles, while the patient experiences pain. Pain and discomfort may also occur when the joint surface of the inner and outer edges of the patella is squeezed by hand. X-rays may show uneven patellar cartilage, localized cartilage destruction or incompleteness, subchondral cystic changes, and osteophytes at the patellar rim and femoral condyles. (4) Cruciate ligament injury: Most people with cruciate ligament injury have a history of trauma. After the injury, the knee joint continues to be painful and swollen, unable to walk or the pain increases when walking; the joint may ring when the knee joint is flexed and extended, and at the same time, displacement between the bones can be felt. Therefore, when the knee joint is rattling or popping, it is important to combine age, history of trauma, clinical features and X-ray examination to determine the exact cause.