If there is no discomfort and other symptoms, it may be normal physiological popping when bending after knee surgery. If there are symptoms such as pain, swelling and activity limitation, it may be caused by excessive muscle tension and traumatic arthritis, which is an abnormal phenomenon. 1. Normal physiological popping: when bending the knee joint after surgery, the liquid and gas in the joint cavity will be squeezed, thus causing creaking, which is a normal physiological popping, usually without discomfort and other symptoms, no need to worry too much, generally without special treatment. 2. Excessive muscle tension: after knee surgery, because of short-term joint swelling, pain and other symptoms, the surrounding muscles will be excessively tense, the joint capsule may also be inactive for a long time to appear a slight contracture, which can make the joint pressure increases in joint activities such as exercise bending, may appear creaking phenomenon, accompanied by joint activity is limited. 3. Traumatic arthritis: may be due to knee trauma or long-term disease, the formation of traumatic arthritis, resulting in friction of the joint surface caused by bone friction sound. Articular cartilage has the function of reducing joint friction. When the articular cartilage is damaged and the articular surface is uneven, the creaking sound will appear when the joint activities such as exercise bending, which is one of the typical symptoms of traumatic arthritis. If the creaking sound is accompanied by pain and other uncomfortable symptoms, it is recommended to consult a doctor in time to clarify the condition.