Knee free body refers to certain tissues of the knee joint peeling off and detaching from their original position, forming free bone mass or free tissue, which may be related to knee injuries and is mostly seen in middle-aged and elderly people. The common symptoms of knee free body include knee movement disorder, knee pain, joint effusion, swelling, and joint popping, which affects normal walking and exercise. Knee free body can cause pain due to the smaller free body being trapped between the joint surfaces, which may cause damage to the joint surfaces of the knee, resulting in severe pain. Pain may also be caused by a number of complications, which include chronic synovitis, knee osteoarthritis, and muscle atrophy. The appearance of free body is recommended to go to the regular hospital to improve the examination, and then standardize the treatment under the advice of the doctor.