Knee pain when going downhill may be caused by chronic strain, acute sprain, knee synovitis and meniscus injury. 1. Chronic strain: climbing for too long may lead to fat pad strain, when going downhill, the fat pad will be subject to wear and tear will increase, then the symptoms of knee pain can appear, manifested as soreness. 2. Acute sprains: improper exertion when going downhill, resulting in sprains in the knee joint area, can also cause symptoms of knee pain, and the pain is more intense, may also be accompanied by swelling and knee joint activity is limited and other symptoms. 3. Knee synovitis: when suffering from knee synovitis and in the recovery period, the symptoms may not be obvious when going up the hill, but when going down the hill, due to the pressure and wear and tear for a long time, it may aggravate the knee synovitis, which will cause knee pain, and the pain is getting more and more intense. 4. Meniscus injury: when the patient has meniscus injury, because going downhill will squeeze the anterior horn of the meniscus and the body, it will pull the synovial membrane to cause knee pain. It may also be accompanied by popping and interlocking. Knee pain when going downhill may also be caused by osteoarthritis, rheumatoid arthritis and ligament injuries, etc. After going downhill, consult a doctor promptly for examination and treatment.