Rustling sound when bending the knee can be caused by physiological factors, patellar dysplasia, osteoarthritis, meniscus injury and other factors. 1. Physiological factors: there is articular cartilage attached to the surface of the knee joint, when the knee joint bending activities, due to the mutual friction between the cartilage and the rustling sound. 2. Patellar dysplasia: patellar dysplasia, there are deformities such as ectropion, can be caused by abnormal friction between the patella and femur when the knee bends, resulting in a rustling sound. 3. Osteoarthritis: Osteoarthritis of the knee joint caused by age or trauma can cause localized osteophytes and destruction of articular cartilage, which can cause abnormal friction between the damaged articular cartilage when the knee joint bends, resulting in rattling sound. 4. Meniscus injury: external direct action or strenuous exercise can cause soft tissue injuries such as meniscus of the knee joint, the damaged meniscus can be embedded in the knee joint, which can make a sound when the joint is bent. When there is a rustling sound when bending the knee, you need to consult a doctor in time, under the guidance of a specialist to actively carry out appropriate treatment, which will help to alleviate the discomfort symptoms as soon as possible.