Symptoms of pain and weakness in the knee joint when walking up stairs may be caused by osteoarthritis of the knee joint, synovitis, meniscus injury and other reasons. 1. Osteoarthritis of the knee joint: with age, excessive weight-bearing labor, obesity and other factors will lead to degenerative changes in the cartilage of the knee joint and osteoarthritis of the knee joint, which will lead to symptoms of pain in the knee joint when going up the stairs. At the same time, with the aggravation of the disease, there will be symptoms of weakness on the stairs. 2. Synovitis: Cold and trauma can lead to aseptic inflammation of the synovial tissue of the knee joint, resulting in edema, hyperplasia and other conditions, which can lead to the symptoms of pain and weakness of the knee on stairs. 3. Meniscus injury: meniscus injury in the knee will lead to local blood flow obstacles, and after the injury will aggravate the irritation of the injury site, causing inflammatory reaction in the knee area, leading to the symptoms of knee pain and weakness on the stairs. There are other causes of knee pain on the stairs can not use force, such as lumbar disc herniation, trauma, etc., such as persistent non-relief, it is recommended to timely visit the hospital, improve the relevant examination, early identification of the cause of the disease, and comply with the doctor’s instructions for targeted treatment, so as to avoid delaying the condition.