The common causes of knee pain after waking up are cold knee joint and acute attack of osteoarthritis of the knee joint, as follows: First, cold knee joint: If you do not pay attention to protecting the knee joint during sleep, resulting in cold knee joint, it can induce acute inflammation of the synovial membrane, resulting in knee pain, swelling and limited movement in the morning, and the symptoms will gradually ease after resting with hot compresses. Second, acute attacks of osteoarthritis of the knee: osteoarthritis of the knee itself is a chronic cumulative disease, which is prone to sudden onset and acute exacerbation after stimulation, such as strain or trauma, resulting in acute pain and limited movement of the knee joint, which can be found on X-ray, while MRI will show fluid in the joint cavity and periarticular edema. Therefore, early diagnosis and treatment of knee pain after waking up from sleep should be carried out so that clinical symptoms can be significantly controlled.