There are several reasons why the legs are always swollen: 1, cardiogenic, that is, the presence of heart failure, this venous reflux disorder is mainly right heart dysfunction, heart failure; 2, nephrogenic, mainly poor kidney function, the formation of proteinuria, hypoproteinemia caused by double lower limbs swelling; 3, vascular elements, including deep venous reflux disorder, deep venous valve insufficiency, the formation of venous stasis; 4. The main reason is that when there is arthritis or bilateral knee osteoarthritis, swelling of the lower extremities also occurs after walking more or standing for a long time, which mainly affects the lymphatic reflux. Clinically, there are mainly these four causes, the last of which is due to the knee joint, which does not easily attract attention and makes it easy for patients not to find the cause of lower limb edema.