Knee sprain for six months can walk normally, recently bending when the cause may be damaged meniscus incomplete recovery or synovitis and so on. 1. Incomplete recovery of meniscus: knee sprain may appear meniscus injury, after half a year of damage to the meniscus stability, integrity has not been fully restored, in the bending activities can appear ringing. 2. synovitis: due to aseptic inflammation six months after the knee sprain, resulting in a decrease in the normal production and absorption of joint fluid, may produce effusion, and sometimes invade the knee cartilage. Rattling may also occur during bending activities. Knee sprains six months can walk normally, recently there may be other reasons for bending noise, should be timely to the regular hospital, the doctor according to the symptoms, signs and auxiliary examination to determine the specific cause.