The tendon pain behind the knee is usually due to pathological factors, such as muscle ligament injury, meniscus injury, popliteal cyst, etc. 1. Muscle ligament injury: if the knee joint activity is not proper, resulting in popliteal muscle, popliteal oblique ligament and other injuries, when the muscles and ligaments are stretched, it will lead to pain behind the knee. 2. Meniscus injury: due to trauma, strain injury, etc., the structure of the meniscus of the knee joint is damaged, when the damaged meniscus is squeezed, the pressure inside the knee joint increases, which will cause pain behind the knee. 3. Popliteal cyst: If the fluid in the joint increases, it may lead to popliteal cyst. When the pressure in the popliteal fossa increases, the ligamentous joint capsule of the popliteal fossa is stimulated, which will lead to pain behind the knee. In addition to the above reasons, osteoarthritis and tumors may also cause tendon pain behind the knee. If the tendon pain at the back of the knee cannot be relieved after resting, it is recommended to go to a regular hospital in time to have the cause clarified by the doctor and then give targeted treatment.