The causes of knee pain in 40-year-old women are many, the most common consideration of degenerative changes in the knee joint, knee injury, bacterial infection, as follows: First, degenerative changes in the knee joint: patients with degenerative changes in the knee joint, such as the presence of osteoarthritis of the knee joint, meniscus injuries, synovitis, which will lead to the presence of significant pain in the knee symptoms. Second, knee injury: when the patient’s knee is subjected to external forces, causing knee meniscus injury, joint capsule injury, fracture, dislocation, ligament injury, will also lead to obvious pain in the knee, and accompanied by swelling, need to carry out general X-ray, CT and MRI examination of the knee, can be clearly diagnosed. Bacterial infection: when the patient’s knee joint is infected by bacteria, it will also lead to obvious pain in the knee, accompanied by swelling, local skin temperature increases. In short, these are the most common causes of knee pain in 40-year-old women.