The causes of cold knees at night are cold knees, synovitis, chondromalacia patella, osteoarthritis and so on. 1. Cold knees: If you don’t pay attention to keep warm or sleep with your legs exposed at night, you may have cold knees for a long time, and you should pay attention to the warmth of your knee joints. 2. Synovitis: There are many causes of synovitis, such as infection, trauma, long-term weight-bearing, etc., may induce this disease. At the onset of the disease, inflammation stimulation, affecting the blood operation, the problem of sleeping with cold knees. 3. Chondromalacia patella: When the knee joint is overloaded for a long time, it is easy to lead to chondromalacia patella, which in turn makes the cartilage of the joint surface degenerate, showing the phenomenon of sensitivity to temperature, and the symptom of cold knees. 4. Osteoarthritis: the cause of osteoarthritis is still unclear, and may be closely related to age, metabolic abnormalities, overloaded joints. When the disease strikes, the blood circulation in the knee area is not smooth, and then the problem of sleeping with cold knees occurs. If the knee is cold at night and there are no other uncomfortable symptoms, you can pay close attention to it for the time being without any special treatment. If it is accompanied by pain and swelling, you should seek medical treatment as soon as possible.