Swelling in the knee and thigh area may be caused by gout, rheumatic diseases, synovitis above the knee and so on. 1. Gout: Gout is a metabolic disorder of the organism, in which the blood uric acid index in the body is elevated leading to hyperuricemia. Urate crystals will be precipitated and deposited in the knee area, resulting in swelling of the knee, and if it affects the blood return to the lower extremities, swelling of the legs will also occur. 2. Rheumatic diseases: Rheumatic diseases are a group of chronic diseases that involve the joints and their surrounding soft tissues. They can cause joint soreness and stiffness, as well as swelling of the knees and thighs. 3. Synovitis above the knee: synovitis may also occur in the knee and leg swelling phenomenon, acute stage, the patient’s leg will appear swelling and even bruising, triggering pain. The affected limbs can be properly elevated to accelerate the venous return of the lower limbs and relieve swelling. In addition to the above reasons, nephritis and other causes may also trigger swelling in the knees and thighs. It is recommended to go to the hospital for timely examination and choose the appropriate treatment under the guidance of the doctor.