Patients suddenly one side of the knee pain symptoms, commonly due to knee trauma, knee inflammation and other reasons, as follows: First, knee trauma: playing basketball and other strenuous exercise in the process of one side of the knee sprain, the patient suddenly knee pain, swelling and limited activities, X-ray film and MRI, sometimes found that the fracture dislocation, ligament tear, meniscus injury, cartilage damage. Second, knee joint inflammation: acute attack of knee osteoarthritis or rheumatoid arthritis, can lead to sudden pain on one side of the knee joint, even affecting weight-bearing, walking, joints can appear stiffness, activity limitation. In addition to pain, the patient will also have muscle spasm and tension on that side, resulting in the lower limbs being unable to walk and bear weight normally. Therefore, if one side of the knee suddenly pain, first of all, should be clear cause and timely treatment, in order to make the symptoms can be completely relieved.