The following causes are mainly considered: 1. Knee synovitis, after the knee joint is cold, the knee joint local ischemia and hypoxia, resulting in anaerobic metabolism, enhanced metabolic products can not be effectively removed, and aseptic inflammation, after the cold will lead to pain, soreness and discomfort significantly aggravated. 2. Knee osteoarthritis, knee joint degeneration and wear and tear of cartilage, resulting in cartilage exfoliation joint gap The main manifestation of osteoarthritis is soreness and painful fluid accumulation in the knee joint, and the effective blood circulation is significantly reduced after exposure to cold, which leads to increased soreness and pain. 3. Osteoarthritis of the knee joint is common in young patients, especially after a lot of exercise, with significant cartilage wear, local fluid accumulation in the knee joint, and after exposure to cold, ischemia and hypoxia can lead to local soreness and pain, and fear of cold.