Unexplainable pain in the knee may be caused by osteophytes, synovitis, minor injuries or other factors. 1. Osteomalacia: the disease starts slowly, without systemic symptoms, and gradually aggravates in the later stage, which may cause indescribable pain in the knee but no pain. 2. Synovitis: the cartilage in the joints is worn out, and the cartilage is not smooth, and the joints feel swollen, itchy, and uncomfortable after activities, but the pain is not serious enough, and the knees may be difficult to describe but not painful. This may be the early stage of knee osteoarthropathy, mild bone change performance. 3. Other factors: around the knee joint in minor injuries, strains, cold, moisture and other adverse factors of stimulation, will lead to local congestion, edema, poor circulation, causing local metabolism relative ischemia, hypoxia, accumulation of anaerobic metabolites in the knee joint, causing discomfort. There are a lot of reasons why the knee is hard to say but not painful, based on the symptoms of the knee is hard to say but not painful can not accurately determine the cause, but also need to be combined with the characteristics of the medical history, other test results to make an accurate judgment, it is recommended that the cause of the disease under the guidance of a doctor.