Pain at the back of the knee may be caused by meniscus injury, or it may be caused by degenerative disease of the knee joint. 1. Meniscus injury: meniscus is a fibrocartilage structure located on the medial and lateral articular surface of the tibial plateau, which serves to maintain the stability of the knee joint as well as cushioning the pressure on the knee joint. Improper exercise or external force may cause meniscus injury and tearing, and if it occurs in the position of the posterior horn of the meniscus, it may cause symptoms of pain at the back of the knee. 2. Degenerative lesions of the knee joint: i.e. osteoarthropathy of the knee joint. Osteoarthropathy of the knee joint mainly occurs in the knee joint, such as osteophytes, synovial hyperplasia and other pathologic changes, which cause the joints to have an increase in impingement or wear and tear during exercise, affecting the normal functioning of the joints, and may also cause symptoms of pain at the back of the knee. The symptoms of pain behind the knee alone sometimes can not accurately determine the cause, but also need to be combined with the characteristics of the medical history, other test results to make an accurate judgment, it is recommended that under the guidance of the doctor to clarify the cause of the disease and targeted treatment.