Rattling knees when walking, commonly due to degenerative osteoarthritis, free bodies in the joints, etc., as follows: First, degenerative osteoarthritis: most cases of elderly patients are degenerative osteoarthritis, patients will have joint pain when walking, joint rattling, and limited joint movement, daily morning can be manifested as joint stiffness symptoms, activity for about 10 minutes that can make the stiffness symptoms completely lifted In addition, X-rays may reveal narrowing of the joint space, while MRI may reveal large areas of articular cartilage and roughness of the joint surface. Second, the free body in the joint: the cartilage in the joint is detached to form a free body, which can cause the patient to have a knee ringing sound when walking, accompanied by small joint interlocking symptoms, and in severe cases can also destroy the joint cartilage, causing severe pain in the joint, which can be found in the general X-ray examination. Surgical treatment can relieve the ringing and post-operative injection of sodium vitreous acid into the joint cavity can lubricate the joint and reduce the ringing.