Possible causes of knee pain on stairs include sports injury, trauma, degenerative changes in the knee joint, popliteal cysts, etc. 1. Sports injury: after strenuous exercise, long-distance running or weight-bearing exercise, pain is caused by synovial edema in the knee joint, which is a normal phenomenon. 2. Traumatic injury: there is a clear history of injury, due to the violent action of the knee meniscus, cruciate ligament, lateral collateral ligament injury or tibia bone contusion, femur bone contusion, when going up and down the stairs, the load on the knee joint increases, pain can occur. 3. Degenerative changes of knee joint: because of old age, weight bearing, mountaineering, obesity, etc., causing degeneration of articular cartilage, osteophytes, when going up and down the stairs, the increased load on the knee joint can cause pain. 4. Popliteal cyst: due to trauma, knee inflammatory response, resulting in increased fluid in the knee joint, increased pressure popliteal cysts, may also be painful when going up and down the stairs. Causes of knee pain on stairs are more reasons, may also be related to lumbar disc herniation, goosefoot bursitis and other diseases, if the symptoms continue to be unrelieved, it is recommended to consult a doctor in a timely manner, to clarify the cause of the disease, and to carry out targeted treatment.