Sleeping at night cold knees have lower extremity vascular diseases and other reasons, as follows: 1, lower extremity vascular diseases: the most common, such as lower extremity occlusive vasculitis, often due to arterial occlusion caused by lower extremity blood supply reduction, there will be a cold limb, often manifested as a cold limb below the knee joint, may be stenosis of the blood vessels or lower extremity thrombosis, which can cause poor local blood circulation, resulting in the feeling of localized coolness. 2, knee joint lesions: including degenerative osteoarthritis, rheumatoid arthritis, synovitis, these diseases will appear cold knees, while in the case of cold, cold invasion, will lead to increased knee pain, aseptic inflammation.